Características microbiológicas do suco de laranja in natura

Sucos de laranja frescos são amplamente consumidos, devido ao seu sabor agradável e por representar uma importante fonte de vitamina C, minerais e carboidratos. Essas características tornam o suco um meio propício ao desenvolvimento de microrganismos, incluindo patógenos capazes de sobreviver em ambientes ácidos, como E. coli, Salmonella e Listeria monocytogenes. A qualidade microbiológica do suco de laranja pode ser avaliada pela contagem de bactérias mesófilas heterotróficas totais, bactérias ácido-láticas (BAL), bolores e leveduras, coliformes totais e fecais, além da detecção direta de patógenos. Neste trabalho foi realizado o acompanhamento dessas características para 50 amostras de suco fresco de marcas comercializadas no Rio de Janeiro. As amostras foram adquiridas e mantidas sob refrigeração a 4ºC, até o momento das análises. Além das contagens mencionadas, foi realizada a pesquisa de E. coli e Salmonella sp. As contagens de microorganismos mesófilos heterotróficos e BAL, para a maioria das amostras, mostraram-se em níveis elevados. O nível de coliformes fecais em 15% das amostras foi acima do permitido pela legislação. Os perfis de susceptibilidade a antimicrobianos de coliformes isolados estavam dentro do previsto para amostras ambientais ou fecais não submetidas a grande pressão seletiva.

Crescimento microbiano em produtos à base de peito de frango durante simulação da cadeia de abastecimento

A presença de microrganismos em produtos alimentícios durante produção, armazenamento, transporte e embalagem é inevitável. Sendo assim, conhecer o comportamento do crescimento microbiano é muito importante para a segurança alimentar e estimativa da vida útil. Neste trabalho foi simulada a cadeia de abastecimento de peitos de frangos cru, salgado e cozido durante 20 dias a -18 ± 0,5 ºC (simulação da expedição industrial no Brasil e transporte por navio até a Europa) e, após o descongelamento, 21 dias a 4 ± 0,5 ºC (simulação da vida útil em supermercado). Os produtos foram analisados quanto a Pseudomonas spp., Salmonella spp., Listeria monocytogenes, Staphylococcus spp. e microrganismos viáveis totais (mesófilos e psicrotróficos). As análises de contagem em placas foram seguidas por testes bioquímicos clássicos para a confirmação de colônias típicas. Em nenhuma das amostras foi detectada a presença de Salmonella spp. ou de Listeria monocytogenes. Em termos de contagem de colônias viáveis totais, durante os primeiros 20 dias (a -18 ºC) a presença de microrganismos se manteve estável em baixos níveis de detecção. Depois do descongelamento, curvas de crescimento microbiano foram observadas. De acordo com os parâmetros microbiológicos de segurança, tempos entre 9 e 11 dias a 4 ºC mostraram-se como os limites para garantir a qualidade destes produtos

Partial purification and characterization of a bacteriocin produced by Enterococcus faecium 130 isolated from mozzarella cheese

Lactic acid bacteria are important in foods as potential probiotics and also due to the ability to produce antimicrobial compounds that can contribute for biopreservation. In this work, the bacteriocin produced by the food isolate Enterococcus faecium 130 was partially purified and characterized. The compound was active against Gram-positive bacteria, including Listeria monocytogenes. It was produced after 4 days of storage at a broad temperature range (4 to 37 °C); it was stable at pH ranging from 2 to 10 with no loss of activity after heating at 100 °C for 15 minutes. Bacteriocin was partially purified by the adsorption-desorption technique, and the analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed a molecular mass of 3.5 to 6.5 kDa. These data encourage studies on application of this bacteriocin in food systems as an additional hurdle to microbial growth.

In vitro antimicrobial properties of plant essential oils thymus vulgaris, cymbopogon citratus and laurus nobilis against five important foodborne pathogens

Several essential oils of condiment and medicinal plants possess proven antimicrobial activity and are of important interest for the food industry. Therefore, the Minimum Inhibitory Concentrations (MIC) of those oils should be determined for various bacteria. MIC varies according to the oil used, the major compounds, and the physiology of the bacterium under study. In the present study, the essential oils of the plants Thymus vulgaris (time), Cymbopogon citratus (lemongrass) and Laurus nobilis (bay) were chemically quantified, and the MIC was determined on the bacteria Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, Listeria monocytogenes ATCC 19117, Salmonella enterica Enteritidis S64, and Pseudomonas aeruginosa ATCC 27853. The essential oil of C. citratus demonstrated bacterial activity at all concentrations tested and against all of the bacteria tested. The majority of essential oil compounds were geranial and neral. The major constituent of T. vulgaris was 1.8-cineol and of L. nobilis was linalool, which presented lower antibacterial activity, followed by 1.8-cineol. The Gram-negative bacteria demonstrated higher resistance to the use of the essential oils tested in this study. E. coli was the least sensitive and was inhibited only by the oils of C. citratus and L. nobilis.

Synergistic and antimicrobial properties of commercial turmeric (Curcuma longa) essential oil against pathogenic bacteria

Several studies have shown the antimicrobial and antioxidant properties of turmeric (Curcuma longa), widely used in food industry as a colorant, among other functions. The aim of this study was to determine the antioxidant and antimicrobial properties of turmeric essential oil against pathogenic bacteria and to study the influence of the addition of ascorbic acid on the prevention of polyphenols oxidation. The commercial turmeric essential oil alone did not show bactericidal activity against the microorganisms studied, Listeria monocytogenes and Salmonella typhimurium, but when combined with ascorbic acid, it showed significant antibacterial activity. The highest antimicrobial activity of turmeric essential oil against Salmonella typhimurium was 15.0 ± 1.41 mm at the concentration of 2.30 mg.mL-1 of essential oil and 2.0 mg.mL-1 of ascorbic acid. With regard to Listeria monocytogenes, the largest zone of inhibition (13.7 ± 0.58 mm) was obtained at the same concentrations. The essential oil showed antioxidant activity of EC50 = 2094.172 µg.mL-1 for the DPPH radical scavenging method and 29% under the concentration of 1.667 mg.mL-1 for the β-carotene bleaching method.

Evaluation of the antimicrobial activity of pecan nut [Carya illinoinensis (Wangenh) C. Koch] shell aqueous extract on minimally processed lettuce leaves

Abstract Pecan nutshell is a residue from food industry that has potential to be used as biopreservative in foods. The objective of this study was to evaluate the antimicrobial activity of pecan nutshell aqueous extract in vitro and its effectiveness to inhibit spoilage microorganisms on lettuce leaves. The results indicate that the aqueous extract presents inhibitory activity against important foodborne pathogenic bacteria such as Listeria monocytogenes, Salmonella Enteritidis, Staphylococcus aureus, Bacillus cereus, Aeromonas hydrophila and Pseudomonas aeruginosa. Antimicrobial activity was not observed against Corynebacterium fimi, Clostridium perfringens, Escherichia coli, and the phytopathogenic fungi tested. When applied onto lettuce leaves, pecan nutshell extract reduced the counts of mesophilic and psychrotrophic bacteria in 2 and 4 log CFU/g, respectively, during storage of leafy for 5 days at refrigeration temperature (5 °C). The extract was not effective to inhibit yeast on lettuce leaves. Thus, the aqueous extract of pecan shell showed great potential to be used as a natural preservative in foods, acting mainly in the inhibition of spoilage and pathogenic bacteria.

Évaluation in vitro de la stérilisation au peroxyde d'hydrogène sur les propriétés biologiques de prothèses utilisées lors de stabilisation du genou chez le chien

Objectif—Comparer les effets de la stérilisation au plasma de gaz de peroxyde d’hydrogène (HPGP) à l’oxyde d’éthylène (EO) et à la vapeur (ST) sur les propriétés physico-chimiques et d’adhésion bactérienne de fils de nylon et de polyéthylène. Design expérimental—Etude in vitro. Matériel—Des brins non stérilisés, stérilisés au HPGP, à l’EO et ST; de fil nylon leader (FNL), de fil de nylon pêche (FNP) et de fil de polyéthylène (PE) ont été utilisés. Méthodes—Une analyse de surface au spectroscope photo-électronique à rayons X (XPS), une mesure de l’angle de contact, une analyse par microscopie à force atomique (AFM) et l’adhésion bactérienne de Staphylococcus intermedius et d’Escherichia Coli ont été testés sur les brins. Résultats—Une oxydation de la surface de tous les échantillons stérilisés a été observée quelque soit la méthode de stérilisation. La stérilisation a augmenté significativement l’angle de contact pour tous les types de fil quelque soit la méthode. La rugosité n’a pas été affectée significativement par la méthode de stérilisation pour le FNL et FNP. L’adhésion bactérienne a été affectée significativement par la méthode de stérilisation. Le PE a un angle de contact, une rugosité et une adhésion bactérienne significativement plus élevée que le FNL et FNP, peu importe la méthode de stérilisation. Conclusion—La stérilisation au HPGP constitue une alternative intéressante à la vapeur et l’EO. Le PE n’est peut être pas un matériel idéal par sa capacité d’adhésion bactérienne. De futures études sont nécessaires pour déterminer la signification clinique de ces trouvailles.

Les macrophages d’ascendance européenne et africaine répondent différemment aux infections bactériennes

Des études antérieures démontrent que les descendants de peuples européens et africains présentent des différences de susceptibilité à certaines maladies infectieuses. Ces différences suggèrent des variations interpopulationnelles de la réponse immunitaire qui résultent probablement de l’adaptation de ces individus aux pathogènes de leur environnement. Nous avons caractérisé la réponse immunitaire chez des descendants de peuples européens et africains à des infections bactériennes. Nous avons infecté des macrophages dérivés de monocytes de 30 Américains d’origine africaine (Africains) et de 31 Américains d’origine européenne (Européens) avec les pathogènes intracellulaires Listeria monocytogenes et Salmonella typhimurium pendant 4 heures, puis nous avons mesuré le niveau d’expression pangénomique des cellules infectées et non infectées par séquençage de l’ARNm. Nous avons estimé le niveau de contrôle de l’infection par les macrophages à 2, 4 et 24 heures post-infection en évaluant le taux de survie des bactéries. Nous avons observé que les Africains présentent significativement moins de bactéries intracellulaires après 4 et 24 heures que les Européens, suggérant que les Africains contrôlent mieux les infections bactériennes. Nous avons identifié des différences interpopulationnelles dans le niveau de sécrétion des cytokines et dans le niveau d’expression de certains gènes, ce qui suggère que les Africains modulent une réponse inflammatoire plus forte que les Européens. Nous avons démontré que plusieurs de ces gènes ont subi des évènements de sélection positive récents seulement chez les Européens. Notre étude a identifié plusieurs gènes candidats susceptibles d’influencer le cours des infections bactériennes chez les humains. Nos résultats indiquent que les différences dans la progression des maladies infectieuses entre les populations européennes et africaines seraient le résultat de la sélection naturelle.

Étude de la différenciation des lymphocytes T CD8+ effecteurs et mémoires : rôle de la cellule présentatrice d’antigène et de la voie de signalisation Notch

Lors d’une infection par un pathogène, des lymphocytes T CD8+ naïfs (LTn) spécifiques de l’antigène sont activés, prolifèrent et se différencient en LT effecteurs (LTe). Les LTe produisent différentes cytokines et acquièrent une activité cytotoxique menant à l’élimination du pathogène. Seulement 5 à 10 % des LTe survivront et se différencieront en LT mémoires (LTm), qui sont capables de répondre plus rapidement lors d’une seconde infection par le même pathogène, contribuant au succès de la vaccination. Toutefois, la compréhension de l’ensemble des mécanismes régulant le développement des LTe et des LTm demeure incomplète. Afin de mieux comprendre les signaux requis pour la différenciation des LT CD8+ lors de la réponse immune, nous avons posé deux hypothèses. Nous avons d’abord proposé que différentes cellules présentatrices d’antigène (CPA) fournissent différents signaux au moment de la reconnaissance antigénique influençant ainsi le devenir des LT CD8+. Vu leur potentiel d’utilisation en immunothérapie, nous avons comparé la capacité d’activation des LT CD8+ par les lymphocytes B activés via le CD40 (CD40-B) et les cellules dendritiques (CD). Nous avons montré que l’immunisation avec des CD40-B induit une réponse effectrice mais, contrairement à l’immunisation avec des CD, pratiquement aucun LTm n’est généré. Les LTe générés sont fonctionnels puisqu’ils sécrètent des cytokines, ont une activité cytotoxique et contrôlent une infection avec Listeria monocytogenes (Lm). Nous proposons qu’une sécrétion plus faible de cytokines par les CD40 B ainsi qu’une interaction plus courte et moins intime avec les LT CD8+ comparativement aux CD contribuent au défaut de différenciation des LTm observé lors de la vaccination avec les CD40-B. Ensuite, nous posé l’hypothèse que, parmi les signaux fournis par les CPA au moment de la reconnaissance antigénique, la voie de signalisation Notch influence le développement des LTe, mais aussi des LTm CD8+ en instaurant un programme génétique particulier. D’abord, grâce à un système in vitro, le rôle de la signalisation Notch dans les moments précoces suivant l’activation du LT CD8+ a été étudié. Ce système nous a permis de démontrer que la voie de signalisation Notch régule directement l’expression de la molécule PD-1. Ensuite, grâce à des souris où il y a délétion des récepteurs Notch1 et Notch2 seulement chez les LT CD8+ matures, un rôle de la voie de signalisation Notch dans la réponse immune des LT CD8+ a été démontré. Nos résultats démontrent que suite à une infection avec Lm ou à une immunisation avec des CD, la signalisation Notch favorise le développement de LTe, exprimant fortement KLRG1 et faiblement CD127, destinés à mourir par apoptose. Toutefois, la signalisation Notch n’a pas influencé la génération de LTm. De façon très intéressante, l’expression des récepteurs Notch influence la production d’IFN- en fonction du contexte d’activation. En effet, suite à une infection avec Lm, l’absence des récepteurs Notch n’affecte pas la production d’IFN- par les LTe, alors qu’elle est diminuée suite à une immunisation avec des CD suggérant un rôle dépendant du contexte pour la voie de signalisation Notch. Nos résultats permettent une meilleure compréhension des signaux fournis par les différentes CPA et de la voie de signalisation Notch, donc des mécanismes moléculaires régulant la différenciation des LT CD8+ lors de la réponse immunitaire, ce qui pourrait ultimement permettre d’améliorer les stratégies de vaccination.

Microbial quality of shrimp products of export trade produced from aquacultured shrimp

Bacteriological quality of individually quick frozen (IQF) shrimp products produced from aquacultured tiger shrimp (Penaeus monodon) has been analysed in terms of aerobic plate count (APC), coliforms, Escherichia coli, coagulase-positive staphylococci, Salmonella, and Listeria monocytogenes. Eight hundred forty-six samples of raw, peeled, and deveined tail-on (RPTO), 928 samples of cooked, peeled, and deveined tail-on (CPTO), 295 samples of headless, undeveined shell-on (HLSO), and 141 samples of raw, peeled, and deveined tail-off (RPND) shrimps were analysed for the above bacteriological parameters. Salmonella was isolated in only one sample of raw, peeled tail-on. Serotyping of the strain revealed that it was S. typhimurium. While none of the cooked, peeled tail-on shrimp samples exceeded the aerobic plate count (APC) of 105 colony forming units per gram (cfu/g), 2.5% of raw, peeled, tail-on, 6.4% of raw, peeled tail-off, and 7.5% of headless shell-on shrimp samples exceeded that level. Coliforms were detected in all the products, though at a low level. Prevalence of coliforms was higher in headless shell-on (26%) shrimps followed by raw, peeled, and deveined tail-off (19%), raw, peeled tail-on (10%), and cooked, peeled tail-on (3.8%) shrimps. While none of the cooked, peeled tail-on shrimp samples were positive for coagulase-positive staphylococci and E. coli, 0.6–1.3% of the raw, peeled tail-on were positive for staphylococci and E. coli, respectively. Prevalence of staphylococci was highest in raw, peeled tail-off (5%) shrimps and the highest prevalence of E. coli (4.8%) was noticed in headless shell-on shrimps. L. monocytogenes was not detected in any of the cooked, peeled tail-on shrimps. Overall results revealed that the plant under investigation had exerted good process control in order to maintain superior bacteriological quality of their products

Characterization of Bacteriocins from Bacillus licheniformis strain BTHT8 and Bacillus subtilis strain BTFK101 isolated from marine sediment

Pathogenic microorganisms such as Bacillus cereus, Listeria Monocytogenes and Staphylococcus sp have caused serious diseases, and consequently contributed to considerable economic loss in the food and agricultural industries. Antibiotics have been practically used to treat these pathogens since penicillin G was discovered more than half a century ago. Many different types of antibiotics have been discovered or synthesized to control pathogenic microorganisms. Repetitive use and misuse of antibiotics by the agricultural and pharmaceutical industries have caused the emergence of multidrug-resistant microorganisms, even to the strongest antibiotics currently available; therefore, the rapid development of more effective antimicrobial compounds is required to keep pace with demand. Bacteria were isolated from marine water and sediment samples collected from various locations off the coast of Cochin and salt pans of Tuticorin using pour plate technique. One hundred and twelve isolates were obtained. Seventeen isolates exhibiting antimicrobial activity were segregated after primary screening. The secondary screening which was aimed at selection of bacteria that produce proteinaceous inhibitory compounds, helped to select five strains viz. BTFK101, BTHT8, BTKM4, BTEK16 and BTSB22. The five isolates inhibited the growth of six Gram positive test organisms viz. B. cereus, B. circulans, B. coagulans, B. pumilus, Staphylococcus aureus and Clostridium perfringens. After quantitative estimation of the bacteriocin production, the two strains BTFK101 and BTHT8 were selected for further study.

Lactic acid bacteria as bioprotective agents against foodborne pathogens and spoilage microorganisms in fresh fruits and vegetables

La present tesi doctoral es centra en l'aplicació dels bacteris de l'àcid lactic (BAL) com a agents bioprotectors davant microorganismes patògens i deteriorants.Es van aïllar i seleccionar BAL de fruites i hortalisses fresques i es van assajar in vitro davant 5 microorganismes fitopatògens i 5 patògens humans.Es van realitzar assajos d'eficàcia en pomes Golden Delicious amb tots els aïllats enfront les infeccions causades pel fong Penicillium expansum. La soca més eficaç era Weissella cibaria TM128, que reduïa el diàmetre de les infeccions en un 50%.Les soques seleccionades es van assajar enfront els patògens Salmonella typhimurium, Escherichia coli i Listeria monocytogenes en enciams Iceberg i pomes Golden Delicious.Els BAL interferien eficientment amb el creixemet de S. typhimurium, and L. monocytogenes, però van mostrar poc efecte enfront E. coli.Finalment, es van realitzar assajos dosi-resposta amb les soques Leuconostoc mesenteroides CM135, CM160 and PM249 enfront L. monocytogenes. De totes les soques assajades, la soca CM160 va ser la més efectiva.

Relationship between sublethal injury and microbial inactivation by the combination of high hydrostatic pressure and citral or tert-butyl hydroquinone

The aim was to investigate (i) the occurrence of sublethal injury in Listeria monocytogenes, Escherichia coli, and Saccharomyces cerevisiae after high hydrostatic pressure (HHP) treatment as a function of the treatment medium pH and composition and (ii) the relationship between the occurrence of sublethal injury and the inactivating effect of a combination of HHP and two antimicrobial compounds, tert-butyl hydroquinone (TBHQ) and citral. The three microorganisms showed a high proportion of sublethally injured cells (up to 99.99% of the surviving population) after HHP. In E. coli and L. monocytogenes, the extent of inactivation and sublethal injury depended on the pH and the composition of the treatment medium, whereas in S. cerevisiae, inactivation and sublethal injury were independent of medium pH or composition under the conditions tested. TBHQ alone was not lethal to E. coli or L. monocytogenes but acted synergistically with HHP and 24-h refrigeration, resulting in a viability decrease of >5 log(10) cycles of both organisms. The antimicrobial effect of citral depended on the microorganism and the treatment medium pH. Acting alone for 24 h under refrigeration, 1,000 ppm of citral caused a reduction of 5 log(10) cycles of E. coli at pH 7.0 and almost 3 log(10) cycles of L. monocytogenes at pH 4.0. The combination of citral and HHP also showed a synergistic effect. Our results have confirmed that the detection of sublethal injury after HHP may contribute to the identification of those treatment conditions under which HHP may act synergistically with other preserving processes.

A novel method for measuring lag times in division of individual bacterial cells using image analysis

A method is presented for determining the time to first division of individual bacterial cells growing on agar media. Bacteria were inoculated onto agar-coated slides and viewed by phase-contrast microscopy. Digital images of the growing bacteria were captured at intervals and the time to first division estimated by calculating the "box area ratio". This is the area of the smallest rectangle that can be drawn around an object, divided by the area of the object itself. The box area ratios of cells were found to increase suddenly during growth at a time that correlated with cell division as estimated by visual inspection of the digital images. This was caused by a change in the orientation of the two daughter cells that occurred when sufficient flexibility arose at their point of attachment. This method was used successfully to generate lag time distributions for populations of Escherichia coli, Listeria monocytogenes and Pseudomonas aeruginosa, but did not work with the coccoid organism Staphylococcus aureus. This method provides an objective measure of the time to first cell division, whilst automation of the data processing allows a large number of cells to be examined per experiment. (c) 2005 Elsevier B.V. All rights reserved.

Effect of pH on the antimicrobial activity and oxidative stability of oil-in-water emulsions containing caffeic acid

Antioxidant properties in food are dependent on various parameters. These include the pH value and interactions with food components, including proteins or metal ions. food components affect antioxidant stability and also influence the properties of microorganisms and their viability. This paper describes an investigation of the effect of pH on the antioxidant and antibacterial properties of caffeic acid in different media. The pH values studied, using an oil-in-water emulsion as model system, were 3, 5 (with and without phosphate buffer), and 9. Effects of mixtures of caffeic acid, bovine serum albumin (BSA), and Fe (III) on oxidative deterioration in the emulsion samples were studied. The results show that the antioxidant activity of caffeic acid was increased by the presence of BSA. This effect was pH dependent and was affected by the presence of iron Ions. Antibacterial properties were also pH dependent. The minimum concentration of caffeic acid required to inhibit some microorganisms in the pH range of 5 to 7 was determined. A concentration of 0.41% (w/w) caffeic acid was enough to inhibit the growth of some of the studied microorganisms in the pH range of 5 to 7. However, near-neutral pH concentrations higher than 0.4% were needed to inhibit some microorganisms, including Listeria monocytogenes, E. coli, and Staphylococcus aureus, in the medium.