No description available.

No description available.

Dispersion is a natural part of a biofilm life cycle in many bacterial species. Dispersion occurs when bacteria revert from a stationary, sessile state to a free-swimming, planktonic state and are freed from a biofilm. Bacterial biofilms consist of proteins, polysaccharides, and extracellular DNA that together make up the extracellular polymeric substances. Surrounded by this mucus-like substance, sessile cells can be extremely difficult to eradicate as compared to the planktonic form of Listeria monocytogenes. Biofilms are robust due to increased surface adherence, inhibition of diffusion of harmful compounds, and increased genetic diversity that exists within a biofilm. As a result, traditional biofilm removal methods are often inadequate; and a novel method for the eradication of Listeria monocytogenes biofilms is needed. Here it is shown that two known biofilm dispersal agents, nitric oxide and cis-2-Decenoic acid, do not induce dispersion in Listeria monocytogenes strain LM23. Nitric oxide and cis-2-Decenoic acid do not influence planktonic cell numbers or biofilm biomass. Ten carbohydrates were screened for their influence on biofilm biomass for use in investigation into natural biofilm dispersion in Listeria monocytogenes strain LM23. Carbohydrate source can significantly increase or decrease biofilm biomass as compared to glucose. Natural biofilm dispersion in Listeria monocytogenes remains inconclusive, yet warrants further investigation. Changes in planktonic cells numbers, sessile cell numbers, and biofilm biomass were tracked under static growth conditions, and suggested a possible dispersion event. However, treatment of biofilms with spent media and observation using scanning electron microscopy did not clarify the results obtained. This research deems the nitric oxide donors, molsidomine (N- (ethoxycarbonyl)-3-(4-morpholinyl)-sydnone imine) and MAHMA NONOate (6-(2-Hydroxy-1-methyl-2-nitrosohydrazino)-N-methyl-1-hexanamine), as well as cis-2-Decenoic acid as ineffective in inducing biofilm dispersion. It also brings about new research questions into natural biofilm dispersion in Listeria monocytogenes.

Rapid detection of live pathogens is of paramount importance to ensure food safety. At present, nucleic acid-based polymerase chain reaction and antibody-based lateral flow assays are the primary methods of choice for rapid detection, but these are prone to interference from inhibitors, and resident microbes. Moreover, the positive results may neither assure virulence potential nor viability of the analyte. In contrast, the mammalian cell-based assay detects pathogen interaction with the host cells and is responsive to only live pathogens, but the short shelf-life of the mammalian cells is the major impediment for its widespread application. An innovative approach to prolong the shelf-life of mammalian cells by using formalin was undertaken. Formalin (4% formaldehyde)-fixed human ileocecal adenocarcinoma cell line, HCT-8 on 24-well tissue culture plates was used for the capture of viable pathogens while an antibody was used for specific detection. The specificity of the <u>M</u>ammalian <u>C</u>ell-based <u>I</u>mmuno<u>A</u>ssay (MaCIA) was validated with <i>Salmonella enterica</i> serovar Enteritidis and Typhimurium as model pathogens and further confirmed against a panel of 15 S. Enteritidis strains, 8 S. Typhimurium,11 other <i>Salmonella</i> serovars, and 14 non-<i>Salmonella</i> spp. The total detection time (sample-to-result) of MaCIA with artificially inoculated ground chicken, eggs, milk, and cake mix at 1-10 CFU/25 g was 16-21 h using a traditional enrichment set up but the detection time was shortened to 10-12 h using direct on-cell (MaCIA) enrichment. Formalin-fixed stable cell monolayers in MaCIA provide longer shelf-life (at least 14 weeks) for possible point-of-need deployment and multi-sample testing on a single plate.

An increase in antimicrobial resistance bacteria has endangered our ability to treat infectious diseases. Lack of good in-vivo model has made it difficult to study antimicrobial resistance. In this study, we have used an inexpensive and short life span in-vivo model namely, Caenorhabditis elegans (C. elegans) to study antimicrobial treatment using pathogenic Escherichia coli O157:H7, a multidrug resistance bacterium that causes life threatening infection in humans. We have investigated the influence of live vs. heat killed non-pathogenic E. coli OP50 (OP50) as a food source on the growth and survival of infected C. elegans mutant AU37 with E. coli O157:H7 in the presence and absence of antibiotics. This is analyzed using a liquid-based C. elegans-E. coli O157:H7 infection assay. C. elegans was synchronized and grown on a lawn of live OP50 till they reached L4-young adult stage. L4-young adults were transferred to liquid medium where the C. elegans was infected with live E. coli O157:H7 or live non-pathogenic OP50 for 24 hours. After infection, C. elegans were fed live or heat killed OP50 depending on the experiment, and the life span and levels of E. coli O157:H7 were monitored, with and without ampicillin treatment in a 96 well transwell plate. Our results indicate that live OP50 is an ideal food source for C. elegans growth and survival to study antimicrobial treatment. C. elegans growth rate and survival decreased in presence of heat killed OP50, which makes heat killed OP50 as a non-ideal food source for antimicrobial assay. Moreover, using live OP50 we have discovered that the ampicillin dose 8mg/ml, 16mg/ml, and 32mg/ml are effective in increasing the survival of C. elegans infected with E. coli O157:H7. However, treatment on C. elegans infected with acid stressed E. coli O157:H7 is controversial.

Call number: LD2668 .T4 1985 W36 / Master of Science

This project addressed if decaying macroalgae and leaf detritus play a major role in the detrital pool of a 7th-order karst riverine system. Decay rates, macroinvertebrates colonization patterns, and change in δ13C values of Cladophora, Platanus occidentalis, and a mix of Acer negundo and A. saccharinum were tracked during summer and autumn months for portions of multiple years. Packs of air-dried Cladophora, Acer, and P. occidentalis were placed in mesh bags and put in groups (n=4) in wire baskets. Seven baskets were submerged in riffle (0.5 m) and deeper run (2 m) habitats. Benthic organic matter was collected with each pack to see if there was a correlation with δ13C signatures of decaying macroproducers to help understand what is entering the detrital food web. Summer 2014 Cladophora and Acer were significantly faster to breakdown than Platanus in both habitats. In autumn‒spring 2014‒2015, Cladophora was significantly faster to breakdown than leaves. Isotopic values of Cladophora were not significantly different than leaves in summer 2014 but were significantly more δ13Cdepleted in the autumn‒spring 2014‒2015. There were no significant differences in macroinvertebrate abundance between the macroproducers for either season. Cladophora had significantly lower macroinvertebrate richness in both seasons, lower shredder abundance, but a significantly higher abundance of clingers. The mean δ13C values of benthic detritus were significantly different than all three macroproducers in the summer and significantly different than Cladophora in the run treatment for autumn‒spring. Seasonality had a strong influence on breakdown rates, leading to greater mass loss of all three species in the warm summer months compared to the cooler autumn‒spring months. The low macroinvertebrate richness and shredder abundance on the decaying macroalga suggests Cladophora may not be consumed by macroinvertebrates but used strictly as habitat. The implication of rapid Cladophora decay during warm seasons, plus few colonizing macroinvertebrate taxa, is that the decaying macroalgae may not pass through a decomposer food web before being remineralized as CO2.

Dressed, bagged whole chickens from three Oregon and several out-of-state processors were purchased from retail markets in each season in 1988. Birds were stored at 3°C for 6 days. Total aerobic microorganisms, total psychrotrophic microorganisms, pseudomonads and fluorescent pseudomonads were determined by appropriate procedures. Total aerobic microorganisms and psychrotrophic microorganisms were counted on standard plate count agar with incubation at 20°C for 3 days and at 5°C for 7 days, respectively. Two media, King's B medium and CFC medium, were used in counting pseudomonads. Fluorescent colonies were observed on King's medium under ultraviolet light. A simple slime smear test was used to determine the sliminess. Sensory evaluation was done by thirteen panelists using 9-point scales. The flavor of cooked white and dark meat and skin, the flavor intensity of cooked white and dark meat and skin, the aroma of raw and simmered meat, the aroma intensity of raw and simmered meat and raw sliminess were evaluated. Simple regression analysis was used to determine the relationships between the microbial parameters and sensory evaluations. The paired t test was used in determining the difference between counts on King's medium and CFC medium. A significance level of 95% was set for all tests. Correlation coefficients were also calculated. All the microbial counts were at or below 10⁷/cm², which indicated from literature comparisons that most of the fryers purchased from retail markets and stored for six days were of acceptable quality. The season had no significant effect on the microbial counts and sensory qualities. The means of flavor of cooked meat and skin and aroma of raw and simmered meat were all above fair. Only the raw aroma intensity was significantly (p<0.05) and strongly correlated (r=-0.88) to the aroma quality. Relationships between microbial counts and flavor of cooked meat and aroma of raw and simmered meat were all significant but the correlations were weak. The narrow range of microbial counts may explain the weakness of the correlations found. The slime smear tests had a positive relationship (p<0.05) to the raw sliminess score by panelists, total aerobic microorganisms, total psychrotrophic microorganisms, pseudomonads, and fluorescent pseudomonads. / Graduation date: 1990

No description available.

Escherichia coli produtoras de toxina de Shiga (STEC) são patógenos veiculados por alimentos capazes de causar desde diarréia branda até severa e sanguinolenta e evoluir para complicações graves como colite hemorrágica, síndrome hemolítica urêmica e púrpura trombótica trombocitopênica. Esses microrganismos têm sido associados a numerosos surtos e vários casos esporádicos de infecções em todo o mundo devido ao consumo de alimentos contaminados. O sorogrupo O157 desse grupo de microrganismos é considerado o principal devido ao seu envolvimento em surtos de doença por STEC, entretanto, muitos casos vêm ocorrendo em todo o mundo devido a cepas patogênicas de STEC não-O157, como O26, O103, O111 e O145. Os objetivos do presente trabalho foram avaliar a ocorrência de STEC em três pontos da linha de abate de bovinos destinados à exportação e em cortes refrigerados de aves e de bovinos comercializados na região da Grande São Paulo; pesquisar a presença dos fatores de virulência dos isolados através dos genes stx1, stx2, eaeA e ehxA; identificar isolados de E. coli O157:H7 pela pesquisa dos genes uidA, rfbO157 e flicH7; verificar a citotoxicidade em células Vero; pesquisar a atividade enterohemolítica dos isolados; avaliar o perfil de suscetibilidade a antimicrobianos; identificar os sorotipos e avaliar a diversidade genética dos isolados de STEC obtidos. Na linha de abate, 201 animais foram amostrados, obtendo-se 603 amostras que compreenderam 201 amostras provenientes do couro, 201 de carcaça e 201 de meia carcaça. No varejo, foram analisadas 100 amostras de cortes de carne bovina e 100 de cortes de frango. A metodologia utilizada para detecção de E. coli sorogrupo O157 foi a preconizada pela ISO 16654, enquanto para os sorogrupos O26, O103, O111 e O145 foi empregada a metodologia descrita pelo \"Surveillance Group for Diseases and Infections of Animals\" (NRM 006). Os isolados obtidos foram confirmados como STEC pela técnica de PCR. Dos 201 animais amostrados, dois (1,0%) foram positivos para STEC, obtendo-se sete isolados (três do animal número 399 e quatro do animal 401) do couro. Não houve o isolamento do microrganismo nas amostras de carcaça e meia carcaça. Os sete isolados apresentaram o perfil stx2, uidA, eaeA, ehxA, rfbO157 e fliCH7 podendo, assim, ser considerados E. coli enterohemorrágica (EHEC) pertencentes ao sorotipo O157:H7. Na avaliação da atividade enterohemolítica, nenhum dos isolados expressou essa proteína e, com relação ao teste de suscetibilidade antimicrobiana, três (42,8%) isolados apresentaram resistência ao ácido nalidíxico e um (14,3%) ao cloranfenicol. O PFGE revelou que as sete cepas de STEC isoladas apresentaram dois perfis genéticos distintos, com similaridade entre eles de 75,3%. STEC não foi detectada nas amostras de carne bovina e de aves comercializadas no varejo. Estes resultados sugerem que, apesar de presente no couro dos animais, o emprego de medidas sanitárias eficientes ao longo da cadeia de produção da carne bovina até sua comercialização na forma de corte, contribui para que o isolamento de STEC nas etapas posteriores seja raro. / Shiga toxin-producing Escherichia coli (STEC) are foodborne pathogens that can cause since mild or severe and bloody diarrhea to serious complications, such as hemorrhagic colitis, hemolytic uremic syndrome and thrombotic thrombocytopenic purpura. These microorganisms have been associated with numerous outbreaks and several sporadic cases worldwide due to consumption of contaminated food, especially meat. E. coli O157 is considered the main serogroup involved in disease outbreaks of STEC, however, many cases have been occurred worldwide due to non-O157, such as O26, O103, O111 and O145 strains. The aims of the present study were to determine the occurrence of STEC at three points of cattle slaughter for exporting and in refrigerated beef and poultry cuts commercialized in the Metropolitan area of Sao Paulo, Brazil; identify the genes that code for the virulence factors stx1, stx2, eaeA and ehxA; detect E. coli O157:H7 strains using uidA, rfbO157 and flicH7 genes; verify the citotoxicity in Vero cells and the enterohemolytic activity; evaluate the antimicrobial susceptibility profile; identify the STEC serotypes and evaluate the genetic diversity of STEC isolates. A total of 603 samples were collected from 201 animals at slaughter. The samples were taken from hide (201), carcass (201) and half-carcass (201) and were always collected from the breast region. At retail, 100 refrigerated beef cuts and 100 chicken cuts were analyzed. The detection of E. coli O157 samples were conducted according to the ISO methodology (16654) and for detection of O26, O103, O111 e O145 serogroups the Surveillance Group for Diseases and Infections of Animals methodology (NRM 006) was used. The isolates were confirmed as STEC by PCR technique. Among 201 animals sampled, two (1,0%) were positive for STEC, obtaining seven isolates from hide (three from animal number 399 and four from animal number 401). The microrganism was not detect in carcass and half carcass samples. The seven isolates carried stx2, uidA, eaeA, ehxA, rfbO157 and fliCH7 genes, so, they can be considered as enterohaemorrhagic E. coli (EHEC) O157:H7 serotype. None of the isolates produced the enterohemolytic activity and three (42,8%) isolates showed resistence to nalidixic acid and one (14,3%) to chloramphenicol. PFGE revealed that the seven STEC strains showed two distinct genetic profiles, with 75.3% of similarity between them. STEC was not detected from beef and poultry cuts commercialized at retail. These results suggest that, although present in animals hides, the STEC isolation at later stages of food chain was rare, probably due to effective sanitary measures to control contamination and transmission of this pathogen along the beef production chain until commercialization.