RESUMEN
The aim of the present study was to determine the survival of Salmonella Typhimurium adapted with sodium lactate (NaL), potassium lactate/sodium acetate mixture (KL/NaA) or sodium acetate (NaA) in simulated gastric fluid (SGF) and during heat treatment. NaL-, KL/NaA- and NaA-adapted cells were prepared by incubating in tryptic soy broth (TSB) containing these salts at 5, 5 and 3% (w/v) concentration levels, respectively, for 24 h at 37 °C. The Baranyi model was used to compare the growth kinetic parameters of adapted cells. The acid and heat resistance of adapted cells were determined by incubating in SGF (pH 2.04) at 37 °C and in TSB at 55.8, 57.8 and 59.8 °C, respectively. Adapted cells had significantly (P < 0.05) longer lag phase duration (LPD) and slower maximum growth rate (MGR) than non-adapted cells. The acid resistance of KL/NaA-adapted cells was not significantly (P > 0.05) different from that of non-adapted cells. NaL-adapted cells were more susceptible to the low pH environment, whereas NaA-adapted cells showed enhanced acid resistance compared to non-adapted and other adapted cells. Unlike acid resistance, both NaL- and NaA-adapted cells showed enhanced heat resistance with increased D-values, regardless of treatment temperatures. Thus, this study indicates that adaptation of S. Typhimurium to 5% NaL or 3% NaA could enhance their ability to survive thermal processes or in the human stomach, possibly increasing the risk of Salmonella outbreaks.
Asunto(s)
Microbiología de Alimentos , Salmonella typhimurium/crecimiento & desarrollo , Acetato de Sodio/farmacología , Lactato de Sodio/farmacología , Adaptación Fisiológica , CalorRESUMEN
Listeria monocytogenes is a foodborne pathogen capable of employing stress adaptive responses to evade a variety of stressors including temperature stress. We employed two-dimensional gel electrophoresis coupled with matrix-assisted laser desorption/ionization-time of flight analysis to study the differential expression of L. monocytogenes (ATCC 43256) soluble proteins at heat shock (60 degrees C) conditions, prolonged heat shock (60 degrees C for 9 minutes) conditions, and thermotolerance-inducing (48 degrees C for 30 minutes followed by 60 degrees C for 9 minutes) conditions. We compared the proteome of L. monocytogenes under these conditions to the proteome at 37 degrees C. Eighteen proteins were differentially expressed at 60 degrees C (6 up-regulated and 12 down-regulated), 21 proteins were differentially expressed (12 up-regulated and 9 down-regulated) when the cells were exposed to 60 degrees C for 9 minutes, and 20 proteins were differentially expressed (10 up-regulated and 10 down-regulated) when cells were initially exposed to 48 degrees C for 30 minutes before 60 degrees C for 9 minutes. There was one unidentifiable protein with observed molecular weight of 50 kDa which was differentially expressed across the three temperature treatments. Thermotolerance-inducing conditions caused the up-regulation of a protein by as much as 12-fold. DnaN, a previously identified stress protein, was up-regulated almost threefold at 60 degrees C. TcsA, a lipoprotein (CD4 T cell-stimulating antigen), and Gap (glyceraldehyde-3-phosphate-dehydrogenase) were selectively expressed under prolonged heat shock conditions suggesting their potential as candidate marker proteins targets for identifying temperature-stressed L. monocytogenes cells.
Asunto(s)
Proteínas Bacterianas/metabolismo , Calor/efectos adversos , Listeria monocytogenes/metabolismo , Proteoma/metabolismo , Estrés Fisiológico , Regulación hacia Abajo , Electroforesis en Gel Bidimensional , Listeria monocytogenes/genética , Proteómica/métodos , Solubilidad , Espectrometría de Masa por Láser de Matriz Asistida de Ionización Desorción , Regulación hacia ArribaRESUMEN
Deliberate or accidental contamination of foods such as milk, soft drinks, and drinking water with infectious agents or toxins is a major concern to health authorities. There is a critical need to develop technologies that can rapidly and efficiently separate and concentrate biothreat agents from food matrices. A key limitation of current centrifugation and filtration technologies is that they are batch processes with extensive hands-on involvement and processing times. The objective of our studies was to evaluate the continuous flow centrifugation (CFC) technique for the rapid separation and concentration of bacterial spores from large volumes of milk. We determined the effectiveness of the CFC technology for concentrating approximately 10(3) bacterial spores in 3.7 liters (1 gal) of whole milk and skim milk, using Bacillus subtilis, Bacillus atrophaeus, and Clostridium sporogenes spores as surrogates for biothreat agents. The spores in the concentrated samples were enumerated by using standard plating techniques. Three independent experiments were performed at 10,000 rpm and 0.7 liters/min flow rate. The mean B. subtilis spore recoveries were 71.3 and 56.5% in skim and whole milk, respectively, and those for B. atrophaeus were 55 and 59.3% in skim and whole milk, respectively. In contrast, mean C. sporogenes spore recoveries were 88.2 and 78.6% in skim and whole milk, respectively. The successful use of CFC to concentrate these bacterial spores from 3.7 liters of milk in 10 min shows promise for rapidly concentrating other spores from large volumes of milk.
Asunto(s)
Bacillus/aislamiento & purificación , Centrifugación/métodos , Clostridium/aislamiento & purificación , Contaminación de Alimentos/análisis , Leche/microbiología , Esporas Bacterianas/aislamiento & purificación , Animales , Recuento de Colonia Microbiana , Seguridad de Productos para el Consumidor , Análisis de Inyección de Flujo , HumanosRESUMEN
In this study, 22 yeast strains isolated from foods were characterized by traditional and molecular techniques. With the help of traditional identification tests, yeast strains were grouped in 12 species belonging to 11 genera as follows: Candida parapsilosis, Rhodotorula mucilaginosa, Debaryomyces hansenii, Cryptococcus humicolus, Cryptococcus albidus, Aureobasidium spp., Hanseniaspora valbyensis, Metschnikowia pulcherrima, Lachancea thermotolerans, Pichia anomala, Geotrichum candidum and Yarrowia lipolytica. The patterns obtained by the digestion of ITS-18S rRNA gene with MspI and HaeIII restriction endonucleases were similar among strains belonging to the same species. With the help of randomly amplified polymorphic DNA (RAPD) analysis performed within the same species, discrimination of M. pulcherrima strains could be achieved.