The fate of E. coli O157:H7 and Salmonella spp. during osmotic dehydration of apples was determined at different processing temperatures, times and calcium chloride (CaCl2) concentrations. Apple slices were inoculated to achieve an 8 log CFU/ apple slice concentration of a five strain mixture of E. coli O157:H7 or Salmonella spp. and were soaked in sucrose solutions (60% w/w). In the first study, apple slices were subjected to osmotic dehydration at three different temperatures: 20°C, 45°C and 60°C. In a second study, CaCl₂ was added in the sucrose solution at concentrations of 2%, 4% and 8% to determine its efficacy as an antimicrobial agent. The storage effect of osmotic dehydrated apples on pathogen survival was also tested for seven days at 4°C. Samples were withdrawn at appropriate time intervals, diluted with 0.1% peptone water and surface plated onto recovery media. Recovery of E. coli O157:H7 was compared on Tryptic Soy Agar + 50 ppm nalidixic acid (TSAN) and MacConkey Sorbitol agar (MCS). Recovery of Salmonella was compared on TSAN and XLD agar. There was lower microbial reduction at the lower temperatures tested with approximately 1.0 and 3.0 log CFU/apple slice reduction at 20°C and 45°C, respectively. The population reduction of cells was highest at 60°C, with an approximate five log reduction for both microorganisms (P<0.001). CaCl₂ used as an additive in the osmotic solution, was associated with slightly higher reduction of both E. coli O157:H7 and Salmonella spp. Greater than a 5 log reduction was observed when the combination of CaCl₂ (8%) and 60°C processing temperature was used. During refrigerated storage E. coli O157:H7 and Salmonella decreased by approximately 4.5 log CFU/apple slice, but were still recoverable via direct plating at Day seven. The results of this study show that the survival of E. coli O157:H7 and Salmonella in osmotically dehydrated fruit is influenced by the osmotic processing method used and the level of additive (i.e., CaCl₂) utilized. Parameters associated with decreased survival of pathogens, and therefore, improve product safety, include increasing temperature and time of processing and increasing concentration of CaCl₂. However, E. coli O157:H7 and Salmonella in artificially contaminated apple slices, survived osmotic dehydration processing and subsequent storage under processing and storage parameters of this study. Therefore, processors who produce osmotically dehydrated fruit must consider the potential food safety impact of the osmotic dehydration processes they choose. / Master of Science

Escherichia coli O157:H7 is an enteric pathogen that can cause severe gastrointestinal disease, sometimes leading to hospitalization and death. These bacteria have a variety of virulence factors that can be encoded for on pathogenicity islands (PAIs). The goal of this study was to characterize specific E. coli O157:H7 PAI deletion mutants using three methods: Phentotype Microarrays (PM), growth curves and survival curves were used to elucidate possible roles for the PAIs. Results from the PM study suggest that PAIs have a role in carbon substrate utilization; i.e., four of the O-island (OI) deletion mutants (OI-87, 98, 102 and 172) and an S-Loop (SL-72) deletion mutant exhibited differences in substrate utilization (gains and losses in utilization) compared to parental O157:H7 strains EDL933 (OI) and Sakai (SL), respectively. All of the mutants with the exception of the OI-135 mutant exhibited differences in level of substrate utilization for substrates shown to have important roles in the bacterium. Cell growth results showed that three OI deletion mutants (OI-55, 87 and 102) and the SL (SL-72) mutant exhibited a difference in rate of growth compared to the parental strains. Cell viability results showed that seven of the OI deletion mutants (OI-51, 55, 98, 108, 135, 172 and 176) exhibited different rates of decline in cell number when transferred to sterile water compared to the parental strain. The results show that removal of PAIs from E. coli O157:H7 can affect carbon utilization, growth and survival demonstrating the importance of PAIs in the ecology of these bacteria. / xx, 208 leaves : ill. (some col.) ; 29 cm

<p style="text-align: justify; ">Glavni cilj ovog rada je bio da se razviju i optimizuju objektivni i merljivi&nbsp;indikatori biolo&scaron;kih rizika po bezbednost mesa trupova, kao i da se &ndash; na osnovu&nbsp;kvalitativne ocene rizika - objektivno sagledaju i uporede performanse glavnih strategija&nbsp;za upravljanje tim rizicima na klanicama za goveda i svinje.<br />Ispitan je potencijal haptoglobina goveda i svinja, podeljenih u grupe na osnovu&nbsp;njihove pred-istorije ili nalaza tokom inspekcije mesa, kao indikatora za njihovu rizičnu&nbsp;kategorizaciju pre klanja u pogledu prisustva patolo&scaron;kih lezija. Svaka životinja je bila&nbsp;podvrgnuta aktuelnoj zvaničnoj inspekciji mesa i određen je nivo haptoglobina u krvnom&nbsp;serumu. I u svinja i u goveda, srednje vrednosti koncentracije haptoglobina su bile&nbsp;značajno vi&scaron;e u grupama kod kojih su detektovane abnormalnosti u odnosu na grupe ovih&nbsp;životinja bez nađenih promena, ali takva korelacija nije utvrđena na nivou individualne<br />životinje. Studija je ukazala da određivanje srednjeg nivoa haptoglobina u grupa životinja&nbsp;namenjenih klanju može da služi kao dodatni, objektivni indikator op&scaron;te prihvatljivosti&nbsp;zdravstvenog statusa i/ili farme porekla životinja, u okviru analize informacija iz lanca&nbsp;hrane kao dela premortalne inspekcije. Ovo je važno zbog dono&scaron;enja odluke o&nbsp;sprovođenju pojednostavljene ili detaljnije postmortalne inspekcije određenih životinja ili&nbsp;grupa životinja na klanicama.&nbsp;U pogledu indikatora rizika od mikrobiolo&scaron;ke kontaminacije obrađenih goveđih&nbsp;trupova, ispitana je mogućnost kori&scaron;ćenja numeričke ocene vizuelne čistoće goveda pre&nbsp;klanja. Vizuelno je ocenjena čistoća kože goveda (na skali od 1 do 4), a zatim su na&nbsp;obrađenim trupovima određeni nivoi generičke mikrobiote i prisustvo Escherichia coli&nbsp;O157. Utvrđena je globalna korelacija između vizuelne čistoće kože i nivoa generičke&nbsp;mikrobiote na obrađenim trupovima, ali su se ti nivoi značajno razlikovali samo između&nbsp;trupova vrlo prljavih goveda (kategorija 4) i svih drugih manje prljavih ili čistih&nbsp;(kategorije 1, 2 i 3). U pogledu vizuelne čistoće goveda i prisustva Escherichia coli O157&nbsp;na obrađenim trupovima, jasna korelacija nije utvrđena. Potvrđena je opravdanost&nbsp;kori&scaron;ćenja sistema vizuelne ocene čistoće goveda i korisnost ove ocene kao jednog od&nbsp;indikatora nivoa rizika od mikrobiolo&scaron;ke kontaminacije obrađenih trupova u pogledu&nbsp;generičke mikrobiote.&nbsp;Takođe, ispitana je mogućnost kori&scaron;ćenja kvantitativnog odnosa između nivoa&nbsp;ulazne (na koži) i finalne (na obrađenim trupovima) mikrobiolo&scaron;ke kontaminacije kao&nbsp;potencijalnog indikatora za rizičnu kategorizaciju goveđih i svinjskih klanica u pogledu&nbsp;njihovih performansi u redukciji rizika od mikrobiolo&scaron;ke kontaminacije mesa. Na&nbsp;kožama i trupovima goveda i svinja su određeni nivoi generičke mikrobiote i prisustvo&nbsp;najznačajnijih patogena u lancu goveđeg (Escherichia coli O157) i svinjskog mesa&nbsp;(Salmonella). Rezultati su pokazali da je odnos statusa kože i obrađenog trupa u pogledu&nbsp;nivoa generičke mikrobiote precizniji i pouzdaniji u diferencijaciji performansi procesne&nbsp;higijene klanica, u poređenju sa zvaničnim aktuelnim kriterijumima procesne higijene&nbsp;navedenim u legislativi Evropske Unije. S druge strane, rezultati su ukazali da kori&scaron;ćenje&nbsp;prevalencije patogena kao parametra u karakterizaciji procesne higijene klanica nije&nbsp;korisno.&nbsp;Pored toga, upoređeni su potencijalni doprinosi glavnih dana&scaron;njih strategija u&nbsp;upravljanju biolo&scaron;kim rizicima za bezbednost mesa na klanicama za goveda i svinje -&nbsp;aktuelne inspekcije mesa i procesne higijene klanice - ukupnom osiguranju biolo&scaron;ke&nbsp;bezbednosti mesa. Kvalitativno su ocenjeni rizici po zdravlje ljudi od alimentarnih&nbsp;hazarda povezanih sa goveđim ili svinjskim mesom, koje je moguće kontrolisati jednom&nbsp;od ove dve strategije na klanicama. Poređenjem nivoa ocenjenih rizika, utvrđeno je da&nbsp;adekvatna procesna higijena danas značajno vi&scaron;e doprinosi ukupnoj biolo&scaron;koj&nbsp;bezbednosti mesa trupova goveda i svinja u odnosu na aktuelnu inspekciju mesa. Ipak, u&nbsp;globalnom sistemu bezbednosti mesa, obe navedene strategije moraju da imaju specifičnu&nbsp;ulogu, shodno oceni rizika od hazarda koje kontroli&scaron;u.&nbsp;Svekupno, ova studija je pružila naučnu osnovu za dalje unapređenje savremenog,&nbsp;longitudinalnog i integrisanog sistema biolo&scaron;ke bezbednosti goveđeg i svinjskog mesa,&nbsp;kao i za kori&scaron;ćenje nekih novih indikatora biolo&scaron;kih rizika u tom sistemu. Istovremeno,&nbsp;ukazala je i na potrebu i smer za dalja/dublja istraživanja za optimizaciju i&nbsp;implementacije tog modernog sistema i predloženih indikatora rizika u praksi.</p> / <p> The main aim of this work was to develop and optimize objective and measurable<br /> indicators of biological risks for the safety of carcass meat, and to - based on qualitative<br /> risk assessment - identify and objectively compare performances of the main risk<br /> management strategies in cattle and pig abattoirs.<br /> The potential of haptoglobin as an indicator of animal pre-slaughter risk<br /> classification regarding the presence of pathological lesions was investigated in cattle and<br /> pigs which were divided into groups, based on their pre-history or meat inspection<br /> findings. Each animal was subjected to the current official meat inspection and blood<br /> serum haptoglobin level determination. In both cattle and pigs, the mean haptoglobin<br /> concentrations were significantly higher in groups with abnormalities than in those<br /> without, but such a correlation was not been established at the level of individual animals.<br /> The study indicated that the mean haptoglobin level in groups of animals intended for<br /> slaughter can be used as an additional, objective indicator of general health status of<br /> animals and/or appropriateness of farm of their origin, when analysing the food chain<br /> information as a part of the ante-mortem inspection. This is important in deciding<br /> whether to perform simplified or detailed post-mortem inspection of certain animals or<br /> groups of animals at abattoirs.<br /> The numerical assessment of cattle cleanliness before slaughter was evaluated as a<br /> risk indicator of dressed beef carcasses&rsquo; microbial contamination. Cattle hide cleanliness<br /> was visually assessed (on a scale of 1 to 4) and levels of generic microbiota and<br /> occurrence of Escherichia coli O157 on dressed carcass were determined. A global<br /> correlation was found between the visual hide cleanliness and generic microbiota levels<br /> on dressed carcasses, but these levels significantly differed only between very dirty cattle<br /> (category 4) and all other less dirty or clean cattle (categories 1, 2 and 3). Regarding the<br /> visual cattle cleanliness and the presence of Escherichia coli O157 on dressed carcasses,<br /> a clear relationship was not determined. The validity of cattle cleanliness visual<br /> assessment system and usefulness of this as an indicator of risk of generic microbiota<br /> contamination of dressed carcasses was confirmed.<br /> Also, the quantitative relationship between the levels of incoming (hide/skin) and<br /> final (dressed carcasses) microbiological contamination was evaluated as an indicator for<br /> risk categorization of cattle and pig abattoirs in terms of their performances in reducing<br /> the risk of microbiological contamination of meat. Levels of generic microbiota and<br /> occurrence of the major pathogens in beef (Escherichia coli O157) and pork chain<br /> (Salmonella) were determined on hides/skins and dressed carcasses. The results showed<br /> that the ratio between generic microbiota levels on dressed carcasses and hides/skins is<br /> more precise and more reliable in the differentiation of process hygiene performances of<br /> abattoirs, compared to the official current process hygiene criteria laid down in the<br /> European Union legislation. On the other hand, the results indicated that the prevalence<br /> of pathogens is not useful as a parameter in the characterization of abattoir process<br /> hygiene.<br /> Additionally, potential contributions of the main current strategies in biological<br /> meat safety risk management in cattle and pig abattoirs - the current meat inspection and<br /> abattoir process hygiene - in ensuring the overall biological safety of meat were<br /> compared. Human health biological foodborne risks associated with beef or pork that can<br /> be controlled by one of the two strategies at abattoirs were qualitatively assessed.<br /> Comparing the levels of assessed risks, it was concluded that adequate process hygiene<br /> currently contributes significantly more to the overall biological safety of beef and pork<br /> VIII<br /> carcasses than current meat inspection. However, in the global meat safety assurance<br /> system, both of these strategies must have a specific role, according to the risk<br /> assessment of hazards which they individually control.<br /> Overall, this study has provided a scientific basis for the further development of<br /> contemporary, longitudinal and integrated risk management system for biological safety<br /> of beef and pork, as well as the use of some new indicators of biological risk in such a<br /> system. At the same time, it has indicated the needs and directions for further and more<br /> intensive research to optimize and implement that modern system and the proposed risk<br /> indicators in practice.</p>

<p>Glavni cilj doktorske disertacije bio je ispitivanje op&scaron;tih odlika industrijski proizvedenih, fermentisanih suvih kobasica u Srbiji i mogućnost dodatnog unapređenja njihove mikrobiolo&scaron;ke bezbednosti. Ispitivani su mikrobiolo&scaron;ki i fizičko-hemiijski pokazatelji u industrijskom proizvodnom lancu sremske kobasice i sudžuka, tipičnih fermentisanih suvih kobasica od svinjskog i goveđeg mesa. U sremskoj kobasici praćeno je prisustvo Salmonella а Escherichia coli O157 u sudžuku. Ispitane su i promene glavnih grupa mikrobiota, pH i aw vrednosti i hemijski sastav proizvoda. Mikrobiolo&scaron;ka kontaminacija u početnim koracima proizvodnje bila je uglavnom visoka. Salmonela je ustanovljena u fazi pripreme nadeva u dva od tri proizvodna pogona, dok je E. coli O157 potvrđena u jednom uzorku usitnjenog mesa i masnog tkiva jednog proizvodnog pogona. Rezultati ispitivanja proizvodnje kobasica slični su rezultatima istraživanja u drugim zemljama. Svi uzorci gotovih sremskih kobasica bili su zadovoljavajućeg nivoa mikrobiolo&scaron;kog kvaliteta, dok većina uzoraka sudžuka nije bila zadovoljavajuća. Početno prisustvo alimentarnih patogena može se smatrati bezbednosnim rizikom.<br />Preživljavanje Salmonella Тyphimurium, Escherichia coli O157 i Listeria monocytogenes tokom proizvodnje i skladi&scaron;tenja inokulisane, sremske kobasice i sudžuka, praćeno je u drugoj fazi istraživanja. Smanjenje brojnosti sva tri patogena u skladu je sa literaturnim podacima i može se zaključiti da postupci uobičajeno primenjeni u industrijskoj proizvodnji sremske kobasice i sudžuka ne osiguravaju uvek, u dovoljnoj meri, mikrobiolo&scaron;ku bezbednost proizvoda. Ispitiana je i mogućnost pasterizacije u cilju redukcije navedenih patogena u kobasicama od svinjskog, odnosno, goveđeg mesa, uz ocenu senzorskog kvaliteta proizvoda. Rezultati su pokazali da Salmonella Typhimurium i E. coli O157 mogu da budu uklonjene pasterizacijom gotovih fermentisanih suvih kobasica а dа senzorske odlike proizvoda i dalje оstanu prihvatljive. L. monoctogenes se pokazala kao patogen koji je značajno otporniji na zagrevanje, u oba tipa kobasica, zbog čega su potrebna dalja istraživanja radi redukcije dо prihvatljivog nivoa.</p> / <p>Glavni cilj doktorske disertacije bio je ispitivanje op&scaron;tih odlika industrijski proizvedenih, fermentisanih suvih kobasica u Srbiji i mogućnost dodatnog unapređenja njihove mikrobiolo&scaron;ke bezbednosti. Ispitivani su mikrobiolo&scaron;ki i fizičko-hemiijski pokazatelji u industrijskom proizvodnom lancu sremske kobasice i sudžuka, tipičnih fermentisanih suvih kobasica od svinjskog i goveđeg mesa. U sremskoj kobasici praćeno je prisustvo Salmonella a Escherichia coli O157 u sudžuku. Ispitane su i promene glavnih grupa mikrobiota, pH i aw vrednosti i hemijski sastav proizvoda. Mikrobiolo&scaron;ka kontaminacija u početnim koracima proizvodnje bila je uglavnom visoka. Salmonela je ustanovljena u fazi pripreme nadeva u dva od tri proizvodna pogona, dok je E. coli O157 potvrđena u jednom uzorku usitnjenog mesa i masnog tkiva jednog proizvodnog pogona. Rezultati ispitivanja proizvodnje kobasica slični su rezultatima istraživanja u drugim zemljama. Svi uzorci gotovih sremskih kobasica bili su zadovoljavajućeg nivoa mikrobiolo&scaron;kog kvaliteta, dok većina uzoraka sudžuka nije bila zadovoljavajuća. Početno prisustvo alimentarnih patogena može se smatrati bezbednosnim rizikom.<br />Preživljavanje Salmonella Typhimurium, Escherichia coli O157 i Listeria monocytogenes tokom proizvodnje i skladi&scaron;tenja inokulisane, sremske kobasice i sudžuka, praćeno je u drugoj fazi istraživanja. Smanjenje brojnosti sva tri patogena u skladu je sa literaturnim podacima i može se zaključiti da postupci uobičajeno primenjeni u industrijskoj proizvodnji sremske kobasice i sudžuka ne osiguravaju uvek, u dovoljnoj meri, mikrobiolo&scaron;ku bezbednost proizvoda. Ispitiana je i mogućnost pasterizacije u cilju redukcije navedenih patogena u kobasicama od svinjskog, odnosno, goveđeg mesa, uz ocenu senzorskog kvaliteta proizvoda. Rezultati su pokazali da Salmonella Typhimurium i E. coli O157 mogu da budu uklonjene pasterizacijom gotovih fermentisanih suvih kobasica a da senzorske odlike proizvoda i dalje ostanu prihvatljive. L. monoctogenes se pokazala kao patogen koji je značajno otporniji na zagrevanje, u oba tipa kobasica, zbog čega su potrebna dalja istraživanja radi redukcije do prihvatljivog nivoa.</p> / <p>The main aim of this doctoral thesis was to investigate the general characteristics of industrially-produced Serbian dry fermented sausages and the possibility of further improving their microbiological safety. Microbiological and physicochemical indicators were studied along the industrial production chains producing Sremska and Sudzuk sausage, typical of dry, fermented sausage prepared from pork or beef, respectively. The occurrences of Salmonella in pork sausages, and of Escherichia coli O157 in beef sausages were determined. Changes in the main groups of microbiota, pH, aw values and the chemical composition of the products were evaluated. Microbiological contamination in the initial stages of production was generally high. Salmonella was confirmed from the batter-preparation phase in two of three production lines, while E. coli O157 was confirmed in one sample of meat and fatty tissue from one production line. The results of this investigation of sausage production were similar to results obtained in other countries. All samples of finished pork sausage were of acceptable microbiological quality, while the majority of beef sausage samples were not microbiologically acceptable. The initial presence of foodborne pathogens can be considered a food safety risk.<br />The survival of Salmonella Тyphimurium, Escherichia coli O157 and Listeria monocytogenes during production and storage of inoculated pork and beef sausages was determined in the second phase of the investigation. All three pathogens declined in numbers in accordance with data from the literature, and it can be concluded that normal measures for pork and beef sausage preparation in industrial production do not always ensure, to a suitable level, the microbiological safety of the products. The possibility of pasteurising finished pork and beef sausages, with the aim of reducing Salmonella Typhimurium and E. coli O157, respectively, was investigated, and at the same time, sensory evaluation of product quality was performed. The results showed that pasteurisation eliminated Salmonella Typhimurium and E. coli O157 from finished dry fermented sausages, while sensory qualities of the products remained acceptable. L. monoctogenes proved to be a significantly more heat-resistant pathogen in both types of sausage, and therefore, further research is required to determine how to reduce numbers of this pathogen to acceptable levels.</p>

O objetivo deste estudo foi verificar a ocorrência de S. aureus e E. coli O157: H7 no leite de vacas com mastite subclínica e no leite de mistura de 42 propriedades leiteiras localizadas em duas regiões do Estado de São Paulo: São Carlos e Ribeirão Preto. Paralelamente, entre os isolados de S. aureus foi objetivo identificar os produtores de toxinas e determinar sua origem epidemiológica. O isolamento de S. aureus foi realizado em agar Baird-Parker (35ºC, 48h) e a confirmação bioquímica através da catalase, coagulase, termonuclease, produção de acetoína e fermentação aeróbia da maltose. O isolamento de E. coli O157: H7 foi realizado em agar Sorbitol MacConkey MUG (35ºC, 24h). Para confirmação utilizaram-se as provas do IMVC e sorologia através do kit Soro Anti E. coli O157. Para a detecção da TSST-1 e das enterotoxinas A, B, C e D utilizou-se aglutinação reversa passiva em látex (RPLA). A identificação epidemiológica dos isolados de S. aureus foi realizada por eletroforese em gel de campo pulsado (PFGE). A ocorrência de S. aureus no leite individual nas regiões 1 (São Carlos) e 2 (Ribeirão Preto) foram 3,9% e 6,7%, respectivamente. Animais pertencentes às propriedades leiteiras com produção entre 400 L e 1.000 L/dia apresentaram maior risco de veiculação de S. aureus através do leite quando comparadas com propriedades com produção 1.000 L/dia. Quanto ao leite de mistura, verificou-se que a ocorrência de S. aureus foi a mesma em ambas as regiões (19%). A produção simultânea das enterotoxinas B e C foi observada em 4,7% dos isolados de leite individual, enquanto que 4,7% produziram enterotoxina A e toxina TSST-1. A produção de TSST-1, isoladamente, foi constatada em 14,3% dos isolados de leite individual e em 25% do leite de mistura. Houve similaridade genética entre os isolados de S. aureus, evidenciando sua dispersão epidemiológica entre as propriedades avaliadas. A ocorrência de E. coli O157: H7 no leite individual foi 1% na região 1 e 1,6% na região 2. No leite de mistura não foi detectada E. coli O157: H7. Ressalte-se a importância de medidas preventivas para assegurar a qualidade do leite durante a ordenha, a fim de evitar a ocorrência de microrganismos patogênicos, principalmente S. aureus, e conseqüentemente prevenir riscos de veiculação de toxinfecções através deste alimento. / The aim of this study was to verify the occurrence of S. aureus and E. coli O157: H7 in the milk from dairy cows with subclinical mastitis and in the bulk milk from 42 dairy farms located in two regions of São Paulo State (Region 1: São Carlos, Region 2: Ribeirão Preto). Among the S. aureus strains isolated, the aim was to identify the toxin producers and their epidemiological origin. The isolation of S. aureus was conducted using Baird-Parker agar, and the strains were confirmed by catalase, coagulase, thermonuclease, maltose aerobic fermentation and acetoin production. The isolation of E. coli O157: H7 was conducted using Sorbitol MacConkey MUG agar. The strains were confirmed by IMVC and serology using anti E. coli O157 sera. Rapid passive latex agglutination was used for detection of TSST-1 and enterotoxigenic strains of S. aureus. The epidemiological identification was performed using pulsed field gel electrophoresis (PFGE). S. aureus was isolated from 3.9% and 6.7% of the individual milk samples from regions 1 and 2, respectively. Dairy cows belonging to farms with milk production ranging from 400 to 1.000 L/day showed higher risk of S. aureus carrying-over, when compared with dairy farms with milk production < 400 L/day and > 1.000 L/day. In bulk milk samples, the occurrence of S. aureus was the same in both regions evaluated (19%). The simultaneous production of enterotoxin B and C was observed in 4.7% of strains isolated from individual milk samples, while 4.7% produced both enterotoxin A and TSST-1. TSST-1 production alone was observed in 14.3% of S. aureus strains isolated from individual milk and 25% of bulk milk samples. S. aureus strains tested by PFGE demonstrated genetic similarity, showing the dispersion patterns of this microorganism among dairy farms. E. coli O157: H7 was isolated from 1% and 1.6% of individual milk samples from regions 1 and 2, respectively, although it was not detected in bulk milk samples. The importance of preventive measures to ensure milk quality during milking extraction is stressed, aiming to avoid pathogenic agents, mainly S. aureus, and therefore, to prevent the carry-over of food borne diseases to humans through milk.

Shiga Toxin produzierende Escherichia coli (STEC) sind wichtige Erreger von Lebensmittelinfektionen und gelten als Hauptverursacher für die Ausbildung einer hämorrhagischen Colitis und dem lebensbedrohlichen hämolytisch-urämischen Syndrom. Als Hauptvirulenzfaktor und wichtigstes Charakteristikum der STEC wird die Fähigkeit angesehen, Shiga Toxine (Stx) zu produzieren. Die genetische Information für deren Produktion ist im Genom lambdoider Prophagen kodiert. Eine Antibiotikatherapie bei STEC-assoziierten Infektionen wird sehr kontrovers diskutiert, da sowohl die Produktion der Stx als auch die Freisetzung der Bakteriophagen in vitro durch antibiotisch wirkende Substanzen stimuliert werden kann. Der enterohämorrhagische E. coli O157:H7 Stamm EDL933 beherbergt insgesamt 18 lambdoide Prophagen und prophagenähnliche Elemente, darunter den Stx1-kodierenden Phagen CP-933V und den Stx2-kodierenden Phagen BP-933W. Ziel der vorliegenden Arbeit war es, den Einfluss des Gyrasehemmers Norfloxacin auf das Gesamttranskriptom von EDL933 mit Hilfe der DNA-Microarraytechnologie und unter Verwendung des MWG E. coli O157 Arrays umfassend zu untersuchen und insbesondere die Expression der Prophagengene zu analysieren. Hierfür wurde der E. coli O157:H7 Stamm EDL933 mit 200 ng/ml Norfloxacin inkubiert, Gesamt-RNA isoliert und diese mittels reverser Transkription in cDNA synthetisiert, wobei ein Einbau von fluoreszenzmarkierten Nukleotiden erfolgte. Diese cDNA wurde mit den auf dem E. coli O157 Array befindlichen Oligonukleotiden hybridisiert. Die Auswertung der Fluoreszenzintensitäten ermöglicht eine Analyse der Genexpression. Infolge der Induktion von EDL933 mit 200 ng/ml Norfloxacin zeigten 118 Spots eine Hochregulation und 122 eine Deregulation von Genen an. Bei genauerer Betrachtung resultierte auf Grund der Inkubation mit Norfloxacin eine erhöhte Expression von 52 Genen der Stx-kodierenden Phagen CP-933V und BP-933W. Insbesondere erfolgte eine erhöhte Regulation von Genen der späten Region des BP-933W. Das stxA2-Gen wurde dabei im Vergleich zur nicht-induzierten Kultur 158-fach stärker exprimiert. Im Falle des Stx1-Phagen wiesen nur einige Gene der frühen Region eine gesteigerte Genaktivität auf. Auffallend war die Hochregulation einzelner Gene der nicht Stx-kodierenden Phagen. Gene des Primärstoffwechsels, u. a. Gene der Aminosäurebiosynthese, des Energiehaushaltes und der Zellteilung zeigten eine verminderte Genaktivität nach Induktion. Diese Ergebnisse weisen darauf hin, dass die verwendete Konzentration von Norfloxacin große Auswirkungen auf das Gesamttranskriptom des untersuchten Stammes haben und insbesondere die Genexpression von zehn im Genom des EDL933 befindlichen Prophagen erhöht wurde. Die durch die Microarrayversuche erhaltenen Expressionsraten wurden durch Quantifizierung der cDNA mittels RT Real-Time PCR Untersuchungen überprüft. Zusammenfassend ist festzustellen, dass Norfloxacin neben der antibiotischen Wirkung in der hier verwendeten geringen Konzentration multiple Effekte auf E. coli O157:H7 ausübt und die Auswirkungen in Zukunft noch detaillierter untersucht werden müssen. Die DNA-Microarraytechnologie und der kommerziell erhältliche E. coli O157 Array ermöglichen diese umfassenden Analyse des Transkriptionsprofils. Im Rahmen dieser Arbeit konnte diese Technologie für Untersuchungen der Genexpression von E. coli O157 etabliert und validiert werden. / Infection with Shiga toxin producing Escherichia coli (STEC) is a serious cause of bloody diarrhea and sporadic cases and outbreaks of food-related diseases such hemorrhagic colitis and the hemolytic uremic syndrome (HUS) worldwide. The use of antibiotics in therapy of STEC-associated diseases has been discussed controversially. Release of phage-encoded Shiga toxins is the major virulence factor of enterhemorrhagic Escherichia coli (EHEC). The genome of the EHEC strain E. coli O157:H7 EDL933 contains 18 prophages or prophages elements, including the Stx1- and Stx2-encoding phages CP-933V and BP-933W. Stx-production and Stx-prophage induction can be stimulated by certain antibiotics, e.g. mitomycinC or UV light. The aim of this study was to investigate the influence of a low concentration of the gyrase inhibitor norfloxacin on the whole transcriptom of E. coli O157:H7 strain EDL933 and particularly on the gene expression of prophages using the DNA-microarraytechnology and the commercial available MWG E. coli O157 Array. To determine this, E. coli O157:H7 cultures were incubated with 200 ng/ml norfloxacin. Total RNA was isolated and labelled with fluorescence dyes during reverse transcription. Following this, the labelled cDNA was hybridized with the commercial E. coli O157 Arrays and the fluorescence intensities were measured, analysed and evaluated with appropriate software. Results of this study have indicated that a low concentration of norfloxacin have profound effects on the trancriptome of E. coli O157:H7. Under the conditions applied (200 ng/ml norfloxacin) and an incubation time of 120 minutes, 118 spots indicated a transcriptional upregulation and 122 spots a transcriptional downregulation of E. coli O157:H7 genes present on the array. In detail, 85 spots could be ascribed to EDL933 phage genes. Fifty-two of them could be assigned to the Shiga toxin encoding phages CP-933V and BP-933W, the others belonged to the non-Stx encoding phages or prophages elements existing in the EDL933 genome. Conspicuous, genes present in the late region of the BP-933W prophage were induced most strongly, up to 158-fold in the case of stxA2. Only some genes present in the early region of the Stx1 encoding phage CP-933V were induced upon induction with norfloxacin. Notably, only some genes of the non-Stx phages of EDL933 appeared to be induced after induction. The additional upregulated genes were related to recombination and stress functions and to E. coli O157:H7 RIMD0509952 genes. The majority of downregulated genes belonging to primary metabolism, such as amino acid biosynthesis, cell division and energy metabolism. In conclusion, an induction of E. coli O157:H7 strain EDL933 with 200 ng/ml norfloxacin has profound effects on the transcriptome of E. coli O157:H7, in particular on the global gene expression of more then ten prophages. The DNA-microarray technology and especially the E. coli O157 Array offer a modern tool for analysis of transcription profiles of the serious pathogen EHEC O157 in response to stress, e.g. antibiotics. In the context of this work, the DNA-microarraytechnology could be established and validated to provide the opportunity for further studies about the global effects on the whole transcriptome of E. coli O157.

[Truncated abstract] The applications of biosensors are rapidly expanding with the increased emphasis placed on the use of technology in the evaluation of food safety and also in military use. The United States food industry carried out 144.3 million microbiological tests in 1999 (Alocilja and Radke, 2003). These numbers are expected to rise with the recently implemented regulatory measures for food safety in the United States. In fact, similar trends in food safety are occurring on a global scale. Furthermore, with the recognition and establishment of Microbial Forensics as a new field of forensics, the interest in biosensor development for the detection of microbes will thrive. Moreover, the recent spate of biocrimes, notably the anthrax scares, has called for newer and improved techniques for the sensitive, rapid and reproducible detection of microbes. Biosensors have the capability to fill this role as an efficient device for microbial detection. There is a wide range of biosensors available for different purposes. In addition, their versatility allows for their overlap in many fields. The quartz crystal microbalance (QCM) is a biosensor that is cost-efficient, sensitive, field-deployable with the ability to perform automated, real-time assays within minutes. The QCM is a mass sensitive device that works on the principle where a change in mass deposited on the crystal is inversely proportional to the change in the resonant frequency of the crystal. Therefore, frequency decreases with increasing mass deposited. The QCM has been used in several studies as a biosensor for the detection of a number of viral and bacterial species. ... High antibody incubation concentration required a shorter antibody incubation duration. Conversely, low antibody incubation concentration required a longer antibody incubation duration. Furthermore, regardless of antibody incubation concentration, a distinct pattern in the rate of antibody binding with time was observed. One hour antigen incubation at ambient room temperature (22.5oC) was sufficient for the efficient binding of the antigens to the immobilized antibody layer. Extension of antigen binding time to 15 hours produced inconsequential differences in readings. The binding efficiency of the quartz crystals after a storage period of 2 to 4 weeks at ambient room temperature (22.5oC) fared better than the crystals that were refrigerated at 4oC. Results showed that 0.2M glycine hydrochloride is a poor reagent for the removal of the antigen layer on the quartz crystals for repeated assay use. The 16-mercaptohexadecanoic acid (MHDA) layer and adsorbed proteins on the quartz crystals can be removed by a mixture of sulphuric acid and hydrogen peroxide, known as a piranha process. This allows the crystals to be repeatedly recoated and reused. Overall, this research provides new insights into the preparation process of the quartz crystals for the specific detection of E. coli O157:H7. Conclusive results have been obtained for several tested parameters and suggestions have been raised for further studies in the optimization of the QCM for the E. coli O157:H7 detection process. With improved knowledge and recognition in the capability of the QCM as a biosensor, the QCM may soon be used in conjunction with conventional techniques for the rapid detection of E. coli O157:H7.

Made available in DSpace on 2014-07-29T15:07:52Z (GMT). No. of bitstreams: 1 rosangela.pdf: 1093995 bytes, checksum: 8b8d62975e344cdccd0d1777e48758b1 (MD5) Previous issue date: 2009-08-31 / Escherichia coli O157:H7 is a serotype that belongs to Shiga toxin-producing Escherichia coli group and it has been incriminated in outbreaks of food poisoning and also as cause of sporadic cases of hemorrhagic colitis and hemolytic uremic syndrome in many countries. In Brazil, there is no data available about outbreaks caused by E. coli O157:H7, but this pathogen has been found often in cattle feces. Taking into consideration the high susceptibility of Minas Frescal cheese to the contamination by E. coli O157:H7 and also considering that milk is frequently associated with outbreaks, the aim of this research was to determinate the occurrence of the pathogen in Minas Frescal cheese, and also to compare techniques for this bacterium detection, such as PCR (Polymerase Chain Reaction) and VIDAS ECO O157® (bioMérieux, Lyon, France) test. Thirty cheese samples were collected from open-air markets in Goiânia and thirty samples were collected from establishments under Federal Inspection located in Goiás that trade their products in supermarkets in Goiânia. The MPN (More probable number) of Thermo-tolerant Coliforms and MPN of E. coli were also determined from the samples. From those samples collected in open air markets, E. coli O157:H7 was detected in 6,67% and 23,33% when the technique used was VIDAS ECO O157® and PCR, respectively. From those samples collected in establishments under Federal Inspection, the bacterium was not detected. There was no significant difference (p>0,05) between VIDAS ECO O157® and PCR for pathogen detection in samples from open air market and establishments under Federal Inspection. No significant difference (p> 0,05) was observed in samples collected from open air market and industries under Federal Inspection when VIDAS ECO O157® was used to E.coli O157:H7 detection. When PCR technique was applied, there was significant difference (p< 0,05) between samples origin. In 86,67% of samples collected from open air markets, Thermo-tolerant Coliforms were detected over the level established in Brazilian legislation, but in samples collected from industries under Federal Inspection, this value was 10%. The Minas Frescal cheese samples collected from open air market were more contaminated by E.coli than those collected from establishments under Federal Inspection and commercialized in supermarkets. / Escherichia coli O157:H7 é um sorotipo de E.coli pertencente ao grupo STEC - E.coli produtora de toxina Shiga - que tem sido incriminado em surtos de toxinfecção alimentar bem como em casos esporádicos de colite hemorrágica e síndrome urêmica hemolítica em vários países. No Brasil não há dados sobre possíveis surtos causados por E. coli O157:H7, mas este patógeno vem sendo frequentemente encontrado em fezes bovinas. Tendo-se em vista a suscetibilidade do queijo Minas Frescal à contaminação por E.coli O157:H7 e que o leite é um dos alimentos mais envolvidos em surtos, objetivou com o presente trabalho determinar a ocorrência deste microrganismo em queijos Minas Frescal, além de comparar as técnicas de reação em cadeia da polimerase (PCR) e teste VIDAS ECO O157®(bioMérieux, Lyon, France) na detecção do patógeno. Para tanto, analisou-se 30 amostras oriundas de feiras livres de Goiânia e 30 de estabelecimentos sob Inspeção Federal localizados em Goiás e que comercializam seus produtos em supermercados de Goiânia. Também foram determinados o Número Mais Provável (NMP) de Coliformes Termotolerantes e NMP de E. coli nestas amostras. Nas amostras oriundas de feiras livres detectouse E.coli O157:H7 em 6,67% e 23,33% quando utilizou-se o VIDAS ECO O157® e PCR, espectivamente. Nas amostras provenientes de estabelecimentos sob Inspeção Federal o microrganismo não foi detectado. Não houve diferença significativa (p>0,05) entre VIDAS ECO O157® e PCR na detecção do patógeno em amostras oriundas de feiras livres e estabelecimentos sob Inspeção Federal. Não observou-se diferença significativa (p> 0,05) entre amostras oriundas de feiras livres e indústrias sob Inspeção Federal quando utilizou-se o VIDAS ECO O157® na detecção de E.coli O157:H7. Quando empregou-se a técnica de PCR, constatou-se diferença (p< 0,05) entre as origens das amostras. Em 86,67% das amostras oriundas de feiras livres detectou-se a presença de Coliformes Termotolerantes acima do nível estabelecido pela legislação enquanto que, nas amostras provenientes de estabelecimentos sob Inspeção Federal esse percentual foi de 10%. As amostras de queijo Minas Frescal provenientes de feiras livres revelaram-se mais contaminadas por E.coli do que as oriundas de estabelecimentos sob Inspeção Federal e comercializadas em supermercados.

O objetivo deste estudo foi verificar a ocorrência de S. aureus e E. coli O157: H7 no leite de vacas com mastite subclínica e no leite de mistura de 42 propriedades leiteiras localizadas em duas regiões do Estado de São Paulo: São Carlos e Ribeirão Preto. Paralelamente, entre os isolados de S. aureus foi objetivo identificar os produtores de toxinas e determinar sua origem epidemiológica. O isolamento de S. aureus foi realizado em agar Baird-Parker (35ºC, 48h) e a confirmação bioquímica através da catalase, coagulase, termonuclease, produção de acetoína e fermentação aeróbia da maltose. O isolamento de E. coli O157: H7 foi realizado em agar Sorbitol MacConkey MUG (35ºC, 24h). Para confirmação utilizaram-se as provas do IMVC e sorologia através do kit Soro Anti E. coli O157. Para a detecção da TSST-1 e das enterotoxinas A, B, C e D utilizou-se aglutinação reversa passiva em látex (RPLA). A identificação epidemiológica dos isolados de S. aureus foi realizada por eletroforese em gel de campo pulsado (PFGE). A ocorrência de S. aureus no leite individual nas regiões 1 (São Carlos) e 2 (Ribeirão Preto) foram 3,9% e 6,7%, respectivamente. Animais pertencentes às propriedades leiteiras com produção entre 400 L e 1.000 L/dia apresentaram maior risco de veiculação de S. aureus através do leite quando comparadas com propriedades com produção 1.000 L/dia. Quanto ao leite de mistura, verificou-se que a ocorrência de S. aureus foi a mesma em ambas as regiões (19%). A produção simultânea das enterotoxinas B e C foi observada em 4,7% dos isolados de leite individual, enquanto que 4,7% produziram enterotoxina A e toxina TSST-1. A produção de TSST-1, isoladamente, foi constatada em 14,3% dos isolados de leite individual e em 25% do leite de mistura. Houve similaridade genética entre os isolados de S. aureus, evidenciando sua dispersão epidemiológica entre as propriedades avaliadas. A ocorrência de E. coli O157: H7 no leite individual foi 1% na região 1 e 1,6% na região 2. No leite de mistura não foi detectada E. coli O157: H7. Ressalte-se a importância de medidas preventivas para assegurar a qualidade do leite durante a ordenha, a fim de evitar a ocorrência de microrganismos patogênicos, principalmente S. aureus, e conseqüentemente prevenir riscos de veiculação de toxinfecções através deste alimento. / The aim of this study was to verify the occurrence of S. aureus and E. coli O157: H7 in the milk from dairy cows with subclinical mastitis and in the bulk milk from 42 dairy farms located in two regions of São Paulo State (Region 1: São Carlos, Region 2: Ribeirão Preto). Among the S. aureus strains isolated, the aim was to identify the toxin producers and their epidemiological origin. The isolation of S. aureus was conducted using Baird-Parker agar, and the strains were confirmed by catalase, coagulase, thermonuclease, maltose aerobic fermentation and acetoin production. The isolation of E. coli O157: H7 was conducted using Sorbitol MacConkey MUG agar. The strains were confirmed by IMVC and serology using anti E. coli O157 sera. Rapid passive latex agglutination was used for detection of TSST-1 and enterotoxigenic strains of S. aureus. The epidemiological identification was performed using pulsed field gel electrophoresis (PFGE). S. aureus was isolated from 3.9% and 6.7% of the individual milk samples from regions 1 and 2, respectively. Dairy cows belonging to farms with milk production ranging from 400 to 1.000 L/day showed higher risk of S. aureus carrying-over, when compared with dairy farms with milk production < 400 L/day and > 1.000 L/day. In bulk milk samples, the occurrence of S. aureus was the same in both regions evaluated (19%). The simultaneous production of enterotoxin B and C was observed in 4.7% of strains isolated from individual milk samples, while 4.7% produced both enterotoxin A and TSST-1. TSST-1 production alone was observed in 14.3% of S. aureus strains isolated from individual milk and 25% of bulk milk samples. S. aureus strains tested by PFGE demonstrated genetic similarity, showing the dispersion patterns of this microorganism among dairy farms. E. coli O157: H7 was isolated from 1% and 1.6% of individual milk samples from regions 1 and 2, respectively, although it was not detected in bulk milk samples. The importance of preventive measures to ensure milk quality during milking extraction is stressed, aiming to avoid pathogenic agents, mainly S. aureus, and therefore, to prevent the carry-over of food borne diseases to humans through milk.

Shiga Toxin produzierende Escherichia coli (STEC) sind wichtige Erreger von Lebensmittelinfektionen und gelten als Hauptverursacher für die Ausbildung einer hämorrhagischen Colitis und dem lebensbedrohlichen hämolytisch-urämischen Syndrom. Als Hauptvirulenzfaktor und wichtigstes Charakteristikum der STEC wird die Fähigkeit angesehen, Shiga Toxine (Stx) zu produzieren. Die genetische Information für deren Produktion ist im Genom lambdoider Prophagen kodiert. Eine Antibiotikatherapie bei STEC-assoziierten Infektionen wird sehr kontrovers diskutiert, da sowohl die Produktion der Stx als auch die Freisetzung der Bakteriophagen in vitro durch antibiotisch wirkende Substanzen stimuliert werden kann. Der enterohämorrhagische E. coli O157:H7 Stamm EDL933 beherbergt insgesamt 18 lambdoide Prophagen und prophagenähnliche Elemente, darunter den Stx1-kodierenden Phagen CP-933V und den Stx2-kodierenden Phagen BP-933W. Ziel der vorliegenden Arbeit war es, den Einfluss des Gyrasehemmers Norfloxacin auf das Gesamttranskriptom von EDL933 mit Hilfe der DNA-Microarraytechnologie und unter Verwendung des MWG E. coli O157 Arrays umfassend zu untersuchen und insbesondere die Expression der Prophagengene zu analysieren. Hierfür wurde der E. coli O157:H7 Stamm EDL933 mit 200 ng/ml Norfloxacin inkubiert, Gesamt-RNA isoliert und diese mittels reverser Transkription in cDNA synthetisiert, wobei ein Einbau von fluoreszenzmarkierten Nukleotiden erfolgte. Diese cDNA wurde mit den auf dem E. coli O157 Array befindlichen Oligonukleotiden hybridisiert. Die Auswertung der Fluoreszenzintensitäten ermöglicht eine Analyse der Genexpression. Infolge der Induktion von EDL933 mit 200 ng/ml Norfloxacin zeigten 118 Spots eine Hochregulation und 122 eine Deregulation von Genen an. Bei genauerer Betrachtung resultierte auf Grund der Inkubation mit Norfloxacin eine erhöhte Expression von 52 Genen der Stx-kodierenden Phagen CP-933V und BP-933W. Insbesondere erfolgte eine erhöhte Regulation von Genen der späten Region des BP-933W. Das stxA2-Gen wurde dabei im Vergleich zur nicht-induzierten Kultur 158-fach stärker exprimiert. Im Falle des Stx1-Phagen wiesen nur einige Gene der frühen Region eine gesteigerte Genaktivität auf. Auffallend war die Hochregulation einzelner Gene der nicht Stx-kodierenden Phagen. Gene des Primärstoffwechsels, u. a. Gene der Aminosäurebiosynthese, des Energiehaushaltes und der Zellteilung zeigten eine verminderte Genaktivität nach Induktion. Diese Ergebnisse weisen darauf hin, dass die verwendete Konzentration von Norfloxacin große Auswirkungen auf das Gesamttranskriptom des untersuchten Stammes haben und insbesondere die Genexpression von zehn im Genom des EDL933 befindlichen Prophagen erhöht wurde. Die durch die Microarrayversuche erhaltenen Expressionsraten wurden durch Quantifizierung der cDNA mittels RT Real-Time PCR Untersuchungen überprüft. Zusammenfassend ist festzustellen, dass Norfloxacin neben der antibiotischen Wirkung in der hier verwendeten geringen Konzentration multiple Effekte auf E. coli O157:H7 ausübt und die Auswirkungen in Zukunft noch detaillierter untersucht werden müssen. Die DNA-Microarraytechnologie und der kommerziell erhältliche E. coli O157 Array ermöglichen diese umfassenden Analyse des Transkriptionsprofils. Im Rahmen dieser Arbeit konnte diese Technologie für Untersuchungen der Genexpression von E. coli O157 etabliert und validiert werden. / Infection with Shiga toxin producing Escherichia coli (STEC) is a serious cause of bloody diarrhea and sporadic cases and outbreaks of food-related diseases such hemorrhagic colitis and the hemolytic uremic syndrome (HUS) worldwide. The use of antibiotics in therapy of STEC-associated diseases has been discussed controversially. Release of phage-encoded Shiga toxins is the major virulence factor of enterhemorrhagic Escherichia coli (EHEC). The genome of the EHEC strain E. coli O157:H7 EDL933 contains 18 prophages or prophages elements, including the Stx1- and Stx2-encoding phages CP-933V and BP-933W. Stx-production and Stx-prophage induction can be stimulated by certain antibiotics, e.g. mitomycinC or UV light. The aim of this study was to investigate the influence of a low concentration of the gyrase inhibitor norfloxacin on the whole transcriptom of E. coli O157:H7 strain EDL933 and particularly on the gene expression of prophages using the DNA-microarraytechnology and the commercial available MWG E. coli O157 Array. To determine this, E. coli O157:H7 cultures were incubated with 200 ng/ml norfloxacin. Total RNA was isolated and labelled with fluorescence dyes during reverse transcription. Following this, the labelled cDNA was hybridized with the commercial E. coli O157 Arrays and the fluorescence intensities were measured, analysed and evaluated with appropriate software. Results of this study have indicated that a low concentration of norfloxacin have profound effects on the trancriptome of E. coli O157:H7. Under the conditions applied (200 ng/ml norfloxacin) and an incubation time of 120 minutes, 118 spots indicated a transcriptional upregulation and 122 spots a transcriptional downregulation of E. coli O157:H7 genes present on the array. In detail, 85 spots could be ascribed to EDL933 phage genes. Fifty-two of them could be assigned to the Shiga toxin encoding phages CP-933V and BP-933W, the others belonged to the non-Stx encoding phages or prophages elements existing in the EDL933 genome. Conspicuous, genes present in the late region of the BP-933W prophage were induced most strongly, up to 158-fold in the case of stxA2. Only some genes present in the early region of the Stx1 encoding phage CP-933V were induced upon induction with norfloxacin. Notably, only some genes of the non-Stx phages of EDL933 appeared to be induced after induction. The additional upregulated genes were related to recombination and stress functions and to E. coli O157:H7 RIMD0509952 genes. The majority of downregulated genes belonging to primary metabolism, such as amino acid biosynthesis, cell division and energy metabolism. In conclusion, an induction of E. coli O157:H7 strain EDL933 with 200 ng/ml norfloxacin has profound effects on the transcriptome of E. coli O157:H7, in particular on the global gene expression of more then ten prophages. The DNA-microarray technology and especially the E. coli O157 Array offer a modern tool for analysis of transcription profiles of the serious pathogen EHEC O157 in response to stress, e.g. antibiotics. In the context of this work, the DNA-microarraytechnology could be established and validated to provide the opportunity for further studies about the global effects on the whole transcriptome of E. coli O157.