Selon un rapport de l’OMS, les maladies infectieuses figurent parmi les 3 causes les plus fréquentes de mortalité en début de vie. En effet, les nouveau-nés présentent une sensibilité particulièrement importante aux infections, de par leur système immunitaire toujours en développement et donc immature. Parmi les particularités de l’immunité néonatale, l’absence de cDCs CD11chigh CD8α+ durant la 1ère semaine de vie rend compte de l’incapacité du nouveau-né à développer des réponses de type Th1 et T CD8+ cytotoxiques, essentielles à la protection contre certains pathogènes comme Listeria monocytogenes (Lm). Mon travail de thèse a porté sur l’ontogénie des DCs conventionnelles CD11chigh CD8α+ et plus particulièrement sur la fonction de cette lignée de DCs en début de vie lors d’une infection par Lm. Au cours de cette étude, nous avons identifié, chez le nouveau-né, une population splénique de cDCs CD11chigh qui expriment les marqueurs CD24, CD205 et Clec9A mais pas le CD8α. Cette population, qui dépend du facteur de transcription Batf3, acquière le CD8α une fois transférée dans une souris adulte. Ces DCs néonatales, que nous nommerons DCs pre-CD8α Clec9A+, constituent donc les précurseurs des DCs CD8α+. L’étude fonctionnelle de ces DCs pre-CD8α Clec9A+ a montré qu’elles étaient capables de phagocyter Lm et de générer des réponses T CD8+ contre cette bactérie. De plus, ces cellules sécrètent de l’IL-12p40 et de manière unique de l’IL-10 en réponse à une stimulation par Lm. Par contre, contrairement aux cDCs CD8α+ adultes, nous n’avons observé aucune production d’IL-12p70 par les DCs pre-CD8α Clec9A+ en conditions physiologiques. Elles ne sécrètent pas non plus d’IL-23. Nous avons également montré que ces sécrétions d’IL-12p40 et d’IL-10 jouaient respectivement un rôle positif et négatif dans l’induction des réponses T CD8+ contre Lm. Ainsi, la génération des réponses T CD8+ contre Lm semble résulter, en début de vie, d’une balance entre la sécrétion de ces 2 cytokines aux propriétés antagonistes. Par ailleurs, nous avons démontré que ces cellules constituaient une cible privilégiée en vue d’améliorer les stratégies vaccinales en début de vie. En effet, l’administration à des nouveau-nés d’une construction anti-Clec9A/OVA, associée au poly(I:C), induit des réponses T CD8+ anti-Lm mémoires protectrices à l’âge adulte. Finalement, nous montrons que le TNF-α produit par les monocytes et les neutrophiles joue un rôle essentiel dans la génération des réponses T CD8+ en régulant notamment le statut et la fonction des DCs pre-CD8α Clec9A+ en début de vie. En effet, cette cytokine modifie, en faveur d’une production d’IL-12p40, la balance IL-12p40/IL-10 sécrétée par celles-ci. L’inhibition de la production d’IL-10 par le TNF-α pourrait s’expliquer au moins en partie par une inhibition de la β-caténine au sein des DCs pre-CD8α Clec9A+. En conclusion, nous avons caractérisé un précurseur des DCs CD8α+ biologiquement actif au sein de la rate du nouveau-né de 3 jours. Celui-ci représente une cible potentielle pour l’amélioration des stratégies vaccinales contre des bactéries intracellulaires ou des virus en début de vie, et ce pour autant que l’on puisse contrôler ses propriétés régulatrices. / Doctorat en Sciences biomédicales et pharmaceutiques (Médecine) / info:eu-repo/semantics/nonPublished

Memoria para optar al Título Profesional de Médico Veterinario / Listeria monocytogenes es la bacteria causante de la enfermedad transmitida por alimentos conocida como listeriosis, la cual se ha visto asociada principalmente a alimentos listos para consumo (LPC). Dentro de los brotes de listeriosis se han visto involucrados los productos hidrobiológicos. En los últimos años, Chile ha aumentado la producción y exportación de este tipo de productos, llegando a diferentes mercados que tienen requisitos sanitarios, los cuales Chile debe cumplir. Los laboratorios, para demostrar que son capaces de realizar un método de análisis microbiológico de manera satisfactoria, pueden realizar un Proceso de Verificación, a través del cual se evalúa el rendimiento del método en un laboratorio específico. Para analizar L. monocytogenes en alimentos, existen diferentes métodos, entre los cuales se encuentran los descritos en las normas ISO 11290-1 para análisis cualitativo, e ISO 11290-2 para análisis cuantitativo. Ambos métodos fueron implementados y verificados en Salmón del Atlántico y en Chorito, en el Laboratorio de Inocuidad de los Alimentos del Departamento de Medicina Preventiva Animal de la Facultad de Ciencias Veterinarias y Pecuarias de la Universidad de Chile. El proceso de verificación se realizó en base a la norma ISO/WD 16140-3. En el método cualitativo, se evaluó si este es capaz de detectar un nivel suficientemente bajo de L. monocytogenes. Como resultado se obtuvo la detección positiva de la bacteria en un 100% de las muestras contaminadas. En el método cuantitativo, las muestras fueron contaminadas con tres niveles de inóculos (102, 103 y 104) de L. monocytogenes, y se evaluó la repetibilidad, reproducibilidad intralaboratorio, exactitud e incertidumbre del método. Los resultados obtenidos en ambos métodos cumplieron con los criterios para la verifiación de éstos. Así, el Laboratorio de Inocuidad de los Alimentos del Departamento de Medicina Preventiva Animal de la Facultad de Ciencias Veterinarias y Pecuarias de la Universidad de Chile, demuestra que tiene las capacidades para realizar ambos métodos en las matrices que fueron probadas, siendo capaz de entregar resultados confiables. / Listeria monocytogenes is the bacterium that causes the foodborne disease known as listeriosis, which has been mainly linked to ready-to-eat (RTE) foods. Hydrobiological products have been involved in listeriosis outbreaks. In recent years, Chile has increased production and export of this type of products, reaching various markets with their own health requirements, which Chile must meet. In order to prove they are capable of performing a microbiological analysis method, laboratories can go through a Verification Process, which evaluates the method’s performance in a specific lab. There are various methods to analyze L. monocytogenes in food, among which are those described in the ISO 11290-1 standard, for qualitative analysis, and ISO 11290-2, for quantitative analysis. Both methods were implemented and verified in the Atlantic Salmon and the Mussel, in the Food Harmlessness Laboratory of the Department of Preventative Animal Medicine of the Faculty of Veterinary and Animal Sciences of the University of Chile. The verification process was carried out according to the ISO/WD 16140-3 standard. It evaluated whether the qualitative method is able to detect a low enough level of L. monocytogenes. The results showed positive bacteria detection in 100% of the contaminated samples. For the quantitative method, the samples were contaminated with three inocula levels (102, 103 and 104) of L. monocytogenes, and it evaluated the method’s repeatability, within-laboratory reproducibility, accuracy and uncertainty. The results obtained for both methods satisfied their verification criteria. This way, the Food Harmlessness Laboratory of the Department of Preventative Animal Medicine of the Faculty of Veterinary and Animal Sciences of the University of Chile demonstrates it has the capabilities to perform both methods in the tested matrices.

Natural Killer (NK) cells, lymphocytes of the innate immune response, play a vital role in controlling infections and in tumor surveillance. NK cells provide protection by direct cytolysis of infected cells and by the production of pro-inflammatory cytokines such as, IFN-γ and TNF-α. Notably, NK cells have recently been identified to regulate the immune response by producing the anti-inflammatory cytokine IL-10. Several other cells can produce IL-10 during infections, however NK cell derived IL-10 can be critical in regulating immune response during early phases of infection and therefore protecting the host from excessive immunopathology. Although the regulatory role of NK cells seems to be plausible, the physiological relevance of NK cell mediated immune regulation during infections has not been demonstrated in detail. To investigate the immunoregulatory function of NK cells, I used Murine Cytomegalovirus (MCMV) infection induced by a high dose challenge and demonstrated that NK cells are a major IL-10 producer during acute stage of the infection. To elucidate the role of NK cell derived IL-10 during infections, I generated NK cell specific IL-10 knockout, NKp46iCre  Il-10flox/flox mice (NK-Il-10-/-) by crossing Il-10flox/flox mice with mice expressing Cre recombinase exclusively under the NK cell specific promoter, NKp46 (NKp46iCre knock-in mice). My results indicated that Cre mediated Il-10 genomic deletion occurred predominantly in NK cells but not in NKT, T and B cells. Enriched NK cells from NK-Il-10-/- mice failed to produce IL-10 upon ex vivo IL-2/IL-12 stimulation. Furthermore, histological analysis of the colon indicated that NK-Il-10-/- mice are free from aberrant inflammation. During sustained MCMV infection, significantly higher production of IFN-γ by CD8+ T cells of NK-Il-10-/- mice in salivary glands indicates that NK cell derived IL-10 contributes to the establishment of the immune suppressive environment in the organ. NK-Il-10-/- mice also demonstrated increased susceptibility to acute Listeria monocytogenes (LM) infection based on enhanced body weight loss. Taken together, I have successfully generated NK-Il-10-/- mice that lack the Il-10 gene exclusively in NK cells. The NK-Il-10-/- mouse can be used as an ideal model to dissect the immunoregulatory role of NK cells during various microbial infections and tumorogenesis.

Listeria monocytogenes is a Gram-positive facultative intracellular bacterium with a wide ecological niche and causes a number of diseases in human and animals. It invades mammalian host cells and escapes from the vacuoles prior to replication in the host cell cytoplasm and infecting adjacent cells via actin-based mobility. Phosphoinositide (PIP) metabolism is essential to mammalian cells in signal transduction, actin remodelling, endosome dynamics and membrane trafficking. Modulation of host PIP metabolism by bacteria PIP phosphatases is important for pathogenicity and virulence of many human pathogens. In this study the function of two L. monocytogenes tyrosine and inositol phosphatases LipA and LipB were studied in vitro. The lipA and lipB deletion mutants generated in EGDe and InlA strains were not affected in invasion but were attenuated in intracellular growth in Caco-2 and Hela M cell lines but not in mouse macrophages. Deletion of lipA or lipB did not affect the actin polymerisation but caused reduced plaque number in the plaque assay. The turnover of five PIPs in Hela M cells during L. monocytogenes infection were studied by expression of fluorescent protein tagged domains that specifically recognizes individual PIPs. L. monocytognenes did not affect the metabolism of PI4P, PI(4,5)P2, PI(3,4,5)P3 but co-localised with PI3P at 1.5 hr post-infection and with PI(3,4)P2 at 6 hr to 24 hr post-infection. The PI(3,4)P2 effector protein lamellipodin was discovered to be recruited to actin-associated L. monocytogenes at 4 hr to 24 hr post-infection in Hela M cells. This discovery leads to the hypothesis of a novel mechanism of lamellipodin-dependant cell-to-cell spread. The lipA mutant was found to be attenuated in PI(3,4)P2 recruitment and therefore hypothesized to participate in the proposed lamellipodin pathway by converting PI(3,5)P2 into PI5P, leading to the activation of PI3K and subsequent production of PI(3,4)P2. LipB showed partial localisation at the Golgi complex when over-expressed in Hela M cells, and it was assumed to act mainly as a protein-tyrosine phosphatase. In summary, this study provides some evidence on L. monocytogenes modulating host PIP metabolism by the production of inositol phosphatases. It gives us a better understanding on the intracellular growth of this pathogenic bacterium, and on the interaction between host and parasite.

Thirteen South African medicinal plants which are used traditionally to treat symptoms associated with Listeria monocytogenes infections, were screened for activity against the pathogen. Different plant parts were extracted separately with ethyl acetate or chloroform. All the extracts were first screened against the bacteria using the disc diffusion method. Zones of inhibition observed in the presence of the chloroform extracts of Eucomis autumnalis, ethyl acetate extracts of Acacia karroo and Plectranthus ecklonii (50 mg/ml) were 12 mm, 14 mm and 15 mm respectively. Active extracts were further tested against the bacteria for minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) using the microtitre dilution method. Ethyl acetate extracts of A. karroo exhibited MIC of 3.1 mg/ml and MBC of 6.25 mg/ml. Ethyl acetate extracts of P. ecklonii showed MIC of 0.5 mg/ml and MBC of 1.0 mg/ml. Five samples namely A. karroo (ethyl acetate extract), P ecklonii (ethyl acetate extract), Senecio inonartus (ethyl acetate extract), S. inonartus (chloroform extract) and Aloe arborescens (ethyl acetate extract) showed good MIC against L. monocytogenes and a MBC range from 1.0 to 12.5 mg/ml. The two plants, A. karroo and P. ecklonii were further selected for the isolation of the active compound(s). Column chromatographic purification of ethyl acetate extracts of the leaves of A. karroo led to the isolation of three known pure compounds namely â-sitosterol, epigallocatechin and epicatechin. The MICs of the â-sitosterol and epigallocatechin that were isolated from A. karrroo were found to be 31.25 µg/ml and 62.5 µg/ml respectively against L. monocytogenes. The confocal scanning laser microscopy (CSLM) showed that the biomass of the listerial biofilms were reduced when the isolated compounds were added and slightly reduced when the crude extract was added. The aggregation of cells which were exposed to â-sitosterol and epigallocatechin was reduced from 25 µm as observed in untreated cells to < 10 µm in length. Therefore as one of the local South African plants identified in the present study, the pure compounds isolated from A. karroo, could be used as a potential natural alternative for eliminating L. monocytogenes biofilms from food processing surfaces. This could help in combating the problem of food contamination and food poisoning caused by the pathogen. It could also help in preparing antibiofilm agents that are cost effective and easily accessible to the public. A. karroo should be further be explored in this regard. The present study reports for the first time the isolation of the three compounds, â-sitosterol, and epicatechin and epigallocatechin from A. karroo. Bioassay-guided fractionation of the P. ecklonii ethyl acetate extract led to the isolation of two known compounds, parvifloron D and parvifloron F. Parvifloron D and F exhibited a minimum inhibitory concentration (MIC) of 15.6 and 31.25 µg/ml respectively against L. monocytogenes. The MICs of parvifloron D and F against a drug-sensitive strain of Mycobacterium tuberculosis were found to be 190 and 95 µg/ml respectively. The ethyl acetate extract of P. ecklonii and its isolated compounds were tested for their activity on tyrosinase inhibition. The concentration of plant extract at which half the tyrosinase activity was inhibited (IC50) was found to be 61.73 ± 2.69 µg/ml. The antibacterial activity of the extract of P. ecklonii and its isolated compounds correlates with the traditional use of the plant for various ailments such as stomach-aches, diarrhoea and skin diseases. This is the first report on the bioactivity of an extract of P. ecklonii and its two compounds. The antibacterial activity of the extracts of A. karroo, P. ecklonii and their isolated compounds correlates with the traditional use of these plants for symptoms associated with listeriosis. / Thesis (PhD)--University of Pretoria, 2011. / Plant Science / unrestricted

Orientador: Mary Luci de Souza Queiroz / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas / Made available in DSpace on 2018-07-18T19:24:46Z (GMT). No. of bitstreams: 1 Bincoletto_Claudia_M.pdf: 1273903 bytes, checksum: fff2b6abb690ce4dc271000f5b6653a7 (MD5) Previous issue date: 1993 / Resumo: Neste trabalho, investigamos os efeitos da exposição ao chumbo sobre o crescimento e diferenciação de células hematopoiéticas, as chamadas células formadoras de colônias (CFCs) da medula óssea de animais infectados e tratados com chumbo. Estudamos também os efeitos da exposição ao metal sobre a atividade dos fatores de crescimento de colônias (CSFs) no soro, assim como a sobrevida deste animais após infecção. Para a realização dos experimentos através da técnica de cultura clonal, em meio semi-sólido, os animais foram infectados com a bactéria Listeria monocytogenes após final do tratamento com acetato de chumbo. Após infecção com esta bactéria ocorre um aumento no número de células formadoras de colônias (CFCs) no baço, assim como nos níveis séricos de fatores estimuladores de colônias (CSFs). Utilizamos duas linhagens de camundongos: Balb\cj, susceptível a Listeria monocytogenes, e C57BI10 resistente a esta infecção. As doses de acetato de chumbo utilizadas foram: 1300, 130 e 13 ppm por períodos de 70, 30 e 10 dias. Ao final do tratamento os animais foram inoculados com doses de 3x102 - Balb\cj e 3x106 - C57BI10 e sacrificados 24, 48 e 72 horas após inoculação. A sobrevida destes animais foi determinada após observação destes camundongos por um período de 10 dias. Nossos resultados demonstraram que o efeito supressor do chumbo foi evidente em ambas linhagens. Na linhagem susceptível à infecção os efeitos da exposição ao chumbo ficou evidente em todos os grupos expostos, infectados ou não, nos três intervalos de tempo estudados após infecção. Nos animais resistentes a esta infecção o efeito supressor do acetato de chumbo também ficou evidente. Nesta linhagem, nas primeiras 24 horas após infecção tanto o chumbo como a infecção apresentaram efeitos supressores. Entretanto após 48 horas o efeito supressor da infecção foi superado, permanecendo apenas o efeito supressor induzido pelo chumbo. Não observamos alterações na atividade dos fatores estimuladores de colônias no soro dos animais em decorrência da administração do chumbo, sugerindo que este metal atue através de ação direta sobre os precursores hematopoiéticos. Observamos também um aumento na mortalidade em animais infectados com doses sub-Ietais de Listeria monocytogenes em ambas linhagens estudadas, quando expostas ao metal / Abstract: In this work we have investigated the effects of lead exposure on the growth and differentiation of hematopoietic cells from bone marrow, the so called colony forming cells (CFCs), in normal and infected mice. We also studied the effects of this exposure the serum activity of hemopoietic colony stimulating factors (CSFs), as well as, the survival of these mice after the infection. For this purpose, we used the technique for the clonal culture of hemopoietic cells in semi-solid medium. Mice were infected with the bacteria Listeria monocytogenes after treatment with lead acetate. Two strains of mice were used: Balb\cj (susceptible to Listeria monocytogenes) and C57BI10 (resistent to this bacteria). The doses of lead acetate were: 1300, 130 and 13ppm in periods of 70, 30 and 10 days. At end of this treatment, mice were infected and killed 24, 48 and 72 hours after the inoculation of the bacteria. The survival of these mice was determineted after a period of ten days. The suppressives effects of lead were observed in both strains in the three different periods studied. The dose-response relationship was observed with the 3 doses of lead used in relation to the effects of the infection, however, we observed that in the resistant strain the suppressives effects were overcome 48 hours after the administration of the baçteria. In the susceptible strain the suppressives effects of the infection were evident in the 3 periods studied. No changes were observed in the serum activity of CSFs due to the administration of lead, thus suggesting that this metal acts by a direct action on the myelopoietic cells. A significant decrease in host resistence, as measured by the mortality rate, was found when both strain of mice, after treatment with 1300ppm of lead for 30 days, were challenged with sub-lethal doses of Listeria monocytogenes / Mestrado / Mestre em Ciências Médicas

No description available.

Seminario de Título entregado a la Universidad de Chile en cumplimiento parcial de los requisitos para optar al Título de Ingeniero en Biotecnología Molecular. / La industria chilena hortofrutícola enfrenta grandes desafíos en el área de inocuidad alimentaria y bioseguridad. Garantizar el cumplimiento de los más altos estándares internacionales, le permite a empresas exportadoras, mantener su liderazgo en los más exigentes y demandantes mercados extranjeros. Para validar la inocuidad de sus productos, una empresa chilena líder en la exportación de fruta congelada, solicitó a Ciencia Pura SpA, una compañía enfocada en I+D+i (investigación, desarrollo e innovación), evaluar algunos de sus protocolos de bioseguridad, los cuales deben garantizar la ausencia de patógenos posiblemente letales y ubicuos, como las bacterias Listeria monocytogenes y ciertas cepas de Escherichia coli. Este seminario de título se desarrolla en el marco de la solución propuesta por Ciencia Pura SpA para satisfacer la solicitud de la empresa solicitante. La investigación desarrollada consta de dos series de experimentos con objetivos distintos: la primera, determinar la efectividad del proceso de lavado de la fruta con una solución de hipoclorito de sodio a diferentes concentraciones, ensayando distintos tiempos de exposición al agente desinfectante, sobre la superficie de fruta previamente inoculada; y la segunda serie, analizar la supervivencia bacteriana en la superficie de fruta inoculada, en condiciones de almacenamiento previas y posteriores a su congelación. Los estudios se realizaron sobre cuatro especies de berries cultivadas con gran éxito económico en territorio nacional: frutillas, frambuesas, moras y arándanos. La disminución de la carga bacteriana, y por ende el éxito del tratamiento o almacenaje, fue evaluada comparando el número de Unidades Formadoras de Colonias (CFU) sobre una placa de agar, al ensayar muestras de la superficie de los frutos, luego de inocularlos, y de someterlos a ensayo de lavado o almacenaje. Las características estudiadas de los protocolos utilizados por la empresa cumplen con las regulaciones demandadas por la industria, sin embargo, la relación entre concentración de cloro y tiempo de exposición al desinfectante podrían no ser las óptimas en todos los casos ensayados. Respecto a los ensayos de supervivencia bacteriana bajo diferentes condiciones de almacenamiento y transporte, un efecto bactericida fue observado en las cuatro especies estudiadas, siendo especialmente destacable en frambuesas. / Food exporting companies are always struggling to ensure their biosafety protocols are up to satisfy the most demanding international markets, focusing on high reliability to guarantee operations overseas. To validate innocuity of their exported goods, an important Chilean food export company, asked Ciencia Pura SpA, a company focused on R&D in the agricultural sector, to evaluate that in their frozen berries production chain the risk of contamination from potentially dangerous microbiological risks, such as the health-threatening bacteria Listeria monocytogenes and Escherichia coli, is nil. This seminar is the result of the research proposed and conducted by Ciencia Pura SpA. The upcoming investigation is divided as two sets of experiments with different objectives: the first one, to determine the disinfection effectiveness of household bleach (sodium hypochlorite dissolution), at different concentrations and exposure times, in the surface of bacteria-inoculated berries; the second set, to analyze bacterial growth in fruit surface at different storage conditions (pre-freezing and freezing temperatures). The research was carried out on four commercially successful berry fruits grown in Chilean territory: straw-, rasp-, black- and blue-berries. Bacterial load of inoculated berries was assessed to determine disinfection efficiency and bacterial survival, comparing Colony Forming Unit (CFU) occurrence in an agar plate culture before and after the treatments. / Agosto 2019

<div><div><div><p>Foodborne pathogens form biofilms as a survival strategy in various unfavorable environments, and biofilms are known to be the frequent source for infection and outbreaks of foodborne illness. Therefore, it is essential to understand the pathogenicity of bacteria in biofilms and methods to inactivate biofilm-forming microbes from food processing environments, including school cafeteria or other community-based food production facilities, and to prevent foodborne outbreaks. Pathogen transmissions occur primarily through raw or under cooked foods and by cross contamination during unsanitary food preparation practices. Then, pathogens can form biofilms on the surface and become persistent in food production facilities and can be a source for recurrent contamination and foodborne outbreaks. In this study, our first aim was to use L. monocytogenes as a model pathogen to study how an enteric infectious pathogen isolated from biofilm modifies its pathogenesis compared to its planktonic counterpart. Both clinical and food isolates with different serotypes and biofilm-forming abilities were selected and tested using cell culture and mouse models. L. monocytogenes sessile cells isolated from biofilms express reduced levels of the lap, inlA, hly, prfA, and sigB and show reduced adhesion, invasion, translocation, and cytotoxicity in the cell culture model than the planktonic cells. Oral challenge of C57BL/6 mice with food, clinical, or murinized-InlA (InlAm) strains revealed that at 12 and 24 h post-infection (hpi), L. monocytogenes burdens are lower in tissues of mice infected with sessile cells than those infected with planktonic cells. However, these differences are negligible at 48 hpi. Besides, the expressions of inlA and lap mRNA in sessile L. monocytogenes from intestinal content are about 6.0- and 280-fold higher than the sessile inoculum, respectively, suggesting sessile L. monocytogenes can still upregulate virulence genes shortly after ingestion (12 h).</p><p>After learning biofilm isolated L. monocytogenes cells have similar virulence potential as the planktonic counterparts, our next goal was to effectively prevent or inactivate biofilms using food-grade natural microbials. Since L. monocytogenes cells are usually found in multi-pathogen biofilm in nature, I combined two food-grade broad-spectrum natural antimicrobials, chitosan nanoparticles (ChNP) and ε-poly-L-lysine (PL), as ChNP-PL nanoconjugates and tested its function on single or mixed culture biofilms of L. monocytogenes, Staphylococcus aureus, Escherichia coli, Salmonella enterica serovar Enteritidis, and Pseudomonas aeruginosa. ChNP- PL not only was able to significantly (P<0.05) prevent the biofilm formation but also inactivate pre-formed biofilms when analyzed by crystal violet staining and plate counting. In vitro cytotoxicity analysis (LDH and WST-based assays) using an intestinal cell line, indicated ChNP- PL to be non-toxic. In conclusion, our results showed ChNP-PL has strong potential to prevent the formation or inactivation of preformed polymicrobial biofilms of foodborne pathogens in food processing environment. Application of ChNP-PL could inhibit the colonization of foodborne pathogens, minimize cross-contamination during food production, and eventually reduce foodborne outbreaks.</p></div></div></div>

La presencia de L. monocytogenes en canales bovinas la convierte en un riesgo potencial de enfermedad para los consumidores por ser causante de la Listeriosis, enfermedad a la que son más susceptibles las mujeres embarazadas y aquellas personas con un sistema inmune deprimido. Debido a ello el objetivo del presente estudio fue evaluar el efecto del ácido láctico a una concentración del 2.5% como descontaminante de canales sobre la presencia de L. monocytogenes presentes en la superficie de las canales bovinas, así como evaluar el comportamiento de esta bacteria en refrigeración y bajo la acción del ácido láctico. El estudio se desarrolló en un centro de beneficio de la ciudad de Lima donde se muestrearon un total 58 canales bovinas al azar divididas en dos grupos. Las muestras tomadas fueron delimitadas por marcos estériles y correspondieron a un área total de 400 cm2 por canal bovina, tomadas de 4 zonas diferentes (cadera, falda, pecho y cuello) mediante método no destructivo de hisopado. Estas muestras fueron enriquecidas en medios de cultivo especificos y sometidas a incubación para determinar finalmente la presencia de L. monocytogenes mediante el empleo de un Kit diagnóstico. En los resultados obtenidos se observaron canales que tuvieron cambios respecto a la presencia de la bacteria sobre la superficie de las canales antes y después de la refrigeración y de la acción del ácido láctico, sin embargo al evaluar los resultados mediante la prueba estadística de McNemar se observa que estos cambios se debieron al azar (p>0.05) para el grupo 1 y para el grupo 2, el cual fue sometido a la acción del ácido láctico, se observa que hay diferencia estadistica significativa (p<0.05) por lo que se demuestra la acción bactericida del ácido láctico al 2.5% contra de L. monocytogenes presentes en la superficie de las canales. Se concluye que el tratamiento con ácido láctico al 2.5% es útil como descontaminante pero su uso no reemplazaría las buenas prácticas ni a la higiene durante el proceso de beneficio o el almacenamiento en las cámaras frigoríficas debido a que el tratamiento tuvo un efecto bactericida en más del 50% pero no en la totalidad de canales bovinas evaluadas. / --- The presence of L. monocytogenes in beef carcasses makes it a potential disease risk to consumers because it causes listeriosis, disease to which are more susceptible pregnant women and those with depressed immune systems. Because of this, the aim of this study was to evaluate the effect of lactic acid at 2.5% of concentration as decontaminating beef carcasses on the presence of L. monocytogenes on the surface of beef carcasses and to assess the behavior of this bacterium in cooling and under the action of lactic acid. The study was conducted in a profit center of Lima where a total 58 bovine carcasses were sampled randomly divided into two groups. The samples were enclosed by sterile frameworks and corresponded to a total area of 400 cm² per bovine carcasses, taken from 4 zones (hip, flank, brisket and neck) by nondestructive method of swabbing. These samples were enriched in specific culture media and finally subjected to incubation for the presence of L. monocytogenes by use of a diagnostic kit. In the results were observed carcasses who had changes for the presence of bacteria on the surface of carcasses before and after chilling and the action of lactic acid, however when evaluating the results by McNemar statistical test notes that these changes were randomized (p>0.05) to group 1 and group 2, which was subjected to the action of lactic acid, it appears that no statistically significant difference (p <0.05) so the bactericidal action of lactic acid 2.5% is shown against L. monocytogenes on the surface of carcasses. We conclude that treatment with 2.5% lactic acid is useful as a decontaminant but its use would not replace good hygiene practices or profit during storage or refrigerated chambers because the treatment had a bactericidal effect in over 50% but not all of bovine carcasses evaluated. Keywords: carcasses, L. monocytogenes, listeriosis, acid, lactic, decontamination / Tesis