Spoilage – bacterial spoilage

International audienceFood products can be spoiled by bacteria, as they provide a rich nutrient source with physicochemical parameters, like pH and water activity, compatible with bacterial growth. In addition, the conditions used during food processing and storage, like temperature, addition of ingredients, and the use of modified atmosphere or vacuum packaging, exert a selective pressure that shapes the development of bacterial communities. Consequently, bacterial spoilage depends on the food matrices, on their production processes, and on their storage conditions. The main characteristics of bacterial spoilage of dairy, meat, and seafood products and products of vegetable origin are presented

Caractérisation moléculaire de l'écosystème microbien complexe de la crevette cuite et étude des flores d'altération

Les crevettes décortiquées cuites sont des denrées considérées comme fragiles d un point de vue microbiologique, et sensibles au processus d altération organoleptique provoqué par le développement de certaines bactéries. Dans le but de mieux maîtriser leur conservation, la caractérisation de l écosystème microbien de ces produits a été réalisée par le biais d une approche polyphasique, combinant des techniques dites culture-dépendantes, qui permettent l identification phénotypique et moléculaire d isolats bactériens, et des méthodes culture-indépendantes avec la PCR-TTGE et la DHPLC, qui génèrent des empreintes génétiques à partir d un mélange d ADN bactérien extrait directement de la matrice crevette. Cette approche a permis de mettre en évidence les principaux genres et espèces de bactéries présents dans la microflore d altération des crevettes décortiquées cuites. Les bactéries lactiques constituaient le groupe bactérien majoritaire avec les principaux genres : Carnobacterium, Vagococcus, Enterococcus. Au sein du genre Vagococcus, une étude de taxonomie plus approfondie a permis de mettre en évidence la nouvelle espèce Vagococcus penaei .sp .nov. Deux autres groupes bactériens importants étaient retrouvés dans cet écosystème : Brochothrix thermosphacta et Serratia liquefaciens-like. Le potentiel d altération de ces bactéries a été étudié en mettant en œuvre des techniques d analyse sensorielle et d analyse des composés volatils produits par ces bactéries, comme la GC-MS. Trois espèces bactériennes se sont révélées les plus actives dans l altération de ce type de produit : Bt. thermosphacta, St. liquefaciens-like et Cb. maltaromaticumCooked and peeled shrimps are considered as fragile foodstuffs from a microbiological point of view and sensitive to the organoleptic spoilage process induced by the growth of certain bacteria. For a better control of their shelf life, the microbial ecosystem characterisation of this product was carried out by a polyphasic approach combining culture-dependent methods, which allow the phenotypical and molecular identification of bacterial isolates, and culture-independent methods with the PCR-TTGE and DHPLC techniques which generate genetic fingerprintings from a bacterial DNA mixture directly extracted from cooked shrimps matrix. This approach has allowed to highlight the main bacterial genus and species present in the spoilage microbiota of cooked and peeled shrimps. Lactic acid bacteria was the major group with the main genus: Carnobacterium, Vagococcus, Enterococcus. Within the Vagococus genus, a more detailed taxonomic study allowed to discover the novel species Vagococcus penaei .sp .nov. Two other important bacterial groups were found in the shrimp ecosystem: Brochothrix thermosphacta and Serratia liquefaciens-like. The spoilage potential of these bacteria has been investigated by using sensory analysis methods and biochemical techniques to determine the volatile compounds produced by these bacteria, like the gas chromatography coupled to mass spectrometry device. Three species were considered as the most spoiling bacteria in this type of product: Bt. thermosphacta, St. liquefaciens-like and Cb. maltaromaticum.NANTES-BU Sciences (441092104) / SudocSudocFranceF

Inhibition of food-spoilage and foodborne pathogenic bacteria by a nisin Z-producing Lactococcus lactis subsp. lactis KT2W2L

The growth of food-spoilage and foodborne pathogenic bacteria was inhibited by a nisin Z-producing Lactococcus lactis subsp. lactis KT2W2L as determined by the agar spot test and agar well diffusion assay. The growth of Brochothrix thermosphacta DSMZ 20171T and Staphylococcus aureus CIP 76.25 was inhibited when co-cultivated with L. lactis subsp. lactis KT2W2L whereas the growth of Escherichia coli CIP 76.24 and Salmonella Enteritidis CIP 81.3 was not. However, the growth level of E. coli CIP 76.24 and S. Enteritidis CIP 81.3 co-cultivated with L. lactis subsp. lactis KT2W2L was diminished compared to cultivation without L. lactis subsp. lactis KT2W2L. The neutralized cell-free supernatant (NCFS) collected from the culture of L. lactis subsp. lactis KT2W2L, cultivated with and without indicator strain, exhibited inhibition zones against the indicator strains as determined by the agar well diffusion assay. The results reported in this study indicate that a nisin Z-producing L. lactis subsp. lactis KT2W2L may find application as a bio-preservative for reducing food-spoilage and foodborne pathogens in food products

Genetic diversity of Brochothrix thermosphacta and food spoilage

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One complete and three draft genome sequences of four Brochothrix thermosphacta strains, CD 337, TAP 175, BSAS1 3 and EBP 3070

Brochothrix thermosphacta is one of the dominant bacterial species associated with spoilage of chilled meat and seafood products through the production of various metabolites responsible for off-odors. However, metabolic pathways leading to meat and seafood spoilage are not all well known. The production of spoiling molecules seems to depend both on strains and on food matrix. Several B. thermosphacta genome sequences have been reported, all issued from meat isolates. Here, we report four genome sequences, one complete and three as drafts. The four B. thermosphacta strains CD 337, TAP 175, BSAS1 3, and EBP 3070 were isolated from different ecological niches (seafood or meat products either spoiled or not and bovine slaughterhouse). These strains known as phenotypically and genetically different were selected to represent intraspecies diversity. CD 337 genome is 2,594,337 bp long, complete and circular, containing 2593 protein coding sequences and 28 RNA genes. TAP 175, BSAS1 3, and EBP 3070 genomes are arranged in 57, 83, and 71 contigs, containing 2515, 2668, and 2611 protein-coding sequences, respectively. These genomes were compared with two other B. thermosphacta complete genome sequences. The main genome content differences between strains are phages, plasmids, restriction/modification systems, and cell surface functions, suggesting a similar metabolic potential but a different niche adaptation capacity

Application of a nisin Z-producing <em>Lactococcus lactis</em> subsp. lactis KT2W2L isolated from brackish water for biopreservation in cooked, peeled and ionized tropical shrimps during storage at 8 °C under modified atmosphere packaging

International audienceLactococcus lactis subsp. lactis KT2W2L was used for biopreservation in cooked, peeled and ionized tropical shrimps (CPITS) during storage at 8 A degrees C under modified atmosphere packaging (MAP). The neutralized and filtered cell-free supernatant produced by this strain exhibited a broad spectrum of inhibition against 23 strains from 24 indicator strains of food-spoilage bacteria and food-borne pathogens by agar well diffusion assay. The growth of Brochothrix thermosphacta CD274, Carnobacterium maltaromaticum CD263 and Listeria innocua CIP 80.11T was inhibited by L. lactis subsp. lactis KT2W2L when co-cultivated at 25 A degrees C. However, only L. innocua CIP 80.11T was inhibited in a co-cultivation at 8 A degrees C. L. lactis subsp. lactis KT2W2L was then used for biopreservation in CPITS. Growth of bacteria group inoculated in CPITS was monitored at regular intervals during storage period under MAP at 8 A degrees C by microbial counts and the thermal temperature gradient gel electrophoresis (TTGE) technique. L. lactis subsp. lactis KT2W2L inhibited the growth of B. thermosphacta and L. innocua CIP 80.11T batches after 7 days of storage. However, it was inactive against C. maltaromaticum batch. The growth of L. lactis subsp. lactis KT2W2L alone or in the presence of indicators increased to reach about 8-9 log CFU/g within 7 days of storage and remained constant until the end of the experiment. In the batches without L. lactis subsp. lactis KT2W2L, all bacterial groups grew well on the cooked shrimp matrix, reaching their maximal levels after 2 weeks of storage. The pH of all homogenized suspensions of MAP-CPITS was quite stable at 6.0-6.7. The control batches were under the enumeration threshold (< 1.70 +/- A 0.00 log CFU/g) until 14 days of storage, and then, an increase in growth was detected on agar plates. In addition, TTGE revealed to be an excellent tool to monitor the change of the microbial ecosystem in this product

Bacteriocin-producing <em>Enterococcus faecalis</em> KT2W2G isolated from mangrove forests in southern Thailand: Purification, characterization and safety evaluation

International audienceThe aim of this work was to purify and characterize the bacteriocin produced by Enterococcus faecalis KT2W2G isolated from the mangrove forest in southern Thailand, in order to evaluate its potential as a new food protective agent. The active peptide from the cell-free supernatant of Ent. faecalis KT2W2G was purified in 4 steps: (i) precipitation with 70% saturated ammonium sulfate, (ii) elution on a reversed phase cartridge (Sep-Pak C8) using different concentrations of acetonitrile, (iii) cation-exchange chromatography and (iv) final purification by reversed phase-HPLC on a C8 column. Each purification step increased the specific activity and reduced the amount of contaminating non-bacteriocin proteins. The specific activity of purified bacteriocin was 13,470.53 AU/mg of protein, which corresponded to a 48.10- fold increase. TricineeSDS-PAGE of the purified bacteriocin gave molecular weight ranging between 3.5 and 6.5 kDa. The activity of the partially purified bacteriocin was unaffected by pH (2.0e12.0) and thermostable, but was sensitive to proteolytic enzymes. This bacteriocin maintained full stability after storage at 20, 4 and 37 C for 2 months. It was stable when incubated for 1 month at 4 C in 0e30% NaCl. Inhibitory spectrum of this bacteriocin showed a wide range of activities against other LAB, foodspoilage and food-borne pathogens. Ent. faecalis KT2W2G was sensitive to kanamycin, tetracycline and vancomycin but resistant to ampicillin, gentamicin and penicillin. PCR amplification demonstrated that Ent. faecalis KT2W2G does not harbor virulence genes cylA, cylB and esp but has virulence genes ace, asa1and efaAfs. The bacteriocin and its producing strain may find application as bio-preservatives for reduction of food-spoilage and food-borne pathogens in food products

Evaluation of the spoilage potential of bacteria isolated from spoiled cooked whole tropical shrimp (Penaeus vannamei) stored under modified atmosphere packaging

The spoilage potential of isolates belonging to five bacterial groups/species (Shewanella baltica, Carnobacterium maltaromaticum, Aeromonas salmonicida, Vibrio sp., “other Gamma-Proteobacteria” [containing one strain of Pseudoalteromonas sp. and one strain of Psychrobacter sp.]) isolated from spoiled cooked and whole tropical shrimp stored under modified atmosphere packaging (MAP) was evaluated by inoculation into ionized cooked and peeled tropical shrimp followed by storage for 32 days at 8°C. Microbial growth and sensory changes were monitored during the storage period. The major spoilage bacterial isolate groups were C. maltaromaticum and S. baltica. In order to characterize their spoilage potential further and to study the effect of their interactions, each of these two specific spoilage organisms (SSO) and one mixed-culture, C. maltaromaticum/S. baltica, were tested using a combination of complementary methods: molecular (PCR-TTGE), sensory, chemical, and conventional microbiological analyses. It was concluded that, in the mixed-culture-inoculated samples, both species groups imposed their spoilage characteristics