Packaging gas selects lactic acid bacterial communities on raw pork.

AIMS: To study the effect of different CO2-rich packaging atmospheres on the composition of lactic acid bacterial communities proliferating on raw pork. METHODS AND RESULTS: Raw pork loin was inoculated with a mixture of 14 lactic acid bacteria (LAB) strains previously associated with meat and packaged with four gas atmospheres: (i) 100% CO2 (ii) 80% N2 20% CO2 (iii) 80% N2, 20% CO2, 0·4% CO and (iv) 80% O2, 20% CO2. The colony counts of LAB, pH and composition of packaging gas were monitored every other day during the storage of 14 days at +6°C. The compositions of lactic acid bacterial communities on pork were evaluated after 7 days of storage with culture-independent, terminal restriction fragment length polymorphism analysis of 16S rRNA gene fragments. After 14 days of storage, the compositions of lactic acid bacterial communities were evaluated using identification of plate-grown LAB isolates by numerical ribopattern analysis. The results showed that (i) high concentration of CO2 in packaging atmosphere favoured Lactobacillus sp. (ii) high concentration of O2 favoured Leuconostoc spp. (iii) atmosphere with 80% N2, 20% CO2 favoured Lactococcus sp. CONCLUSIONS: The composition of modified packaging atmosphere is a major factor selecting lactic acid bacterial communities proliferating on raw meat. SIGNIFICANCE AND IMPACT OF THE STUDY: The study provides an explanation for the compositions of lactic bacterial communities on modified atmosphere packaged raw meat observed in other studies. The results should be considered when attempting to manipulate LAB communities in raw meat, e.g. by protective cultures.

The effect of marination on lactic acid bacteria communities in raw broiler fillet strips.

Marination with marinade containing salt, sugar, and acetic acid is commonly used in Finland to enhance the value of raw broiler meat. In this study, we investigated the effect of marination, marinade components and storage time on composition of bacterial communities in modified atmosphere-packaged (MAP) broiler fillet strips. The communities were characterized using two culture-independent methods: 16S rRNA gene fragment sequencing and terminal restriction fragment length polymorphism. In unmarinated broiler fillet strips, Lactococcus spp. and Carnobacterium spp. predominated at the early storage phase but were partially replaced by Lactobacillus spp. and Leuconostoc spp. when the chilled storage time was extended. In the marinated fillet strips, Lactobacillus spp. and Leuconostoc spp. predominated independent from the storage time. By mixing the different marinade components with broiler meat, we showed that marination changed the community composition and favored Leuconostoc spp. and Lactobacillus spp. by the combined effect of carbohydrates and acetic acid in marinade. Marination increased the maximum level of lactic acid bacteria in broiler meat and enhanced CO(2) production and acidification of meat during the chilled storage. Accumulation of CO(2) in package head-space due to the enhanced growth of Leuconostoc spp. in marinated meat may lead to bulging of packages, which is a spoilage defect frequently associated with marinated and MAP raw broiler preparations in Finland.

Comparison of microbial communities in marinated and unmarinated broiler meat by metagenomics.

Most raw poultry sold in Finland at the retail level is mixed with marinades containing oil, sugar, spices and acetic acid and packaged under modified atmosphere. Premature spoilage of marinated poultry preparations has been observed and associated with high levels of Leuconostoc spp. in meat. In this study we investigated whether marination of broiler fillet strips increased the proportion of Leuconostoc spp. in the microbial communities. To obtain a comprehensive view of the microbiota, we sequenced total DNA and 16S rRNA gene amplicons from the microbial communities. The lactic acid bacterial communities were characterized also by identification of colonies. The results showed that marinade increased the proportions of the spoilage-associated Leuconostoc gasicomitatum in the communities as well as the proportions of Leuconostoc gelidum and Lactobacillus spp. The proportions of Carnobacterium, Vagococcus, Brochothrix thrermosphacta, Clostridium, Enterobacteriaceae and Vibrio were diminished in marinated meat. Analysis of 16S rRNA gene amplicons resulted in 312 and 284 operational taxonomical units (dissimilarity 0.03) in unmarinated and marinated meat, respectively, indicating that the meat communities were more diverse than hitherto shown. Metagenomic analysis revealed a number of bacterial taxa that have not been associated with late shelf-life meat before, including Vagococcus and Vibrio that belonged to the predominating part of the microbial community in unmarinated meat. According to the functional analysis of the metagenomes, the communities in both marinated and unmarinated poultry were characterized by high proportions (15.6% or 17.9%) of genes involved in carbohydrate metabolism.

Characterization of psychrotrophic bacterial communities in modified atmosphere-packed meat with terminal restriction fragment length polymorphism.

Characterization of psychrotrophic lactic acid bacteria (LAB) and Brochothrix thermosphacta communities is needed to understand the microbial ecology of spoilage of modified atmosphere-packed (MAP) meats. To overcome the limitations of the currently used methods for the characterization of psychrotrophic bacterial communities in meat, we developed a culture-independent, 16S rRNA gene-targeted terminal restriction fragment length polymorphism (T-RFLP) method. An identification library consisting of 100 Gram-positive and 30 Gram-negative meat-associated bacterial strains was set up to identify the terminal restriction fragments derived from the communities. The taxonomic resolution level of the T-RFLP method was in between genus and species within the investigated LAB strains and within family and genus within the investigated Gram-negative strains. The established library was applied to identify the members of bacterial communities in MAP minced meat at the end of the shelf life. The T-RFLP results and plate counts on Man-Rogosa-Sharpe, Violet Red Bile Glucose, and Streptomycin sulfate thallium acetate actidione agars indicated that LAB and B. thermosphacta predominated in meat. The bacterial taxa associated with the T-RFLP results were compared to those identified among plate-grown LAB isolates by numerical ribopattern analysis. Both methods agreed that Leuconostoc spp. and Carnobacterium spp. prevailed in the LAB community in minced meat followed by Lactobacillus algidus, Lactococcus spp. and Weissella spp. Colony identification revealed that Leuconostoc gasicomitatum, L. gelidum, Carnobacterium divergens and C. maltaromaticum were the predominant LAB species. The T-RFLP results were shown to correlate with viable counts of Leuconostoc spp. and B. thermosphacta. The T-RFLP method was found to be a useful tool enabling rapid and high-throughput characterization of psychrotrophic bacteria prevailing in MAP meat.

Differential cancer predisposition in Lynch syndrome: insights from molecular analysis of brain and urinary tract tumors.

Hereditary non-polyposis colorectal carcinoma (Lynch syndrome) is among the most common hereditary cancers in man and a model of cancers arising through deficient DNA mismatch repair (MMR). Lynch syndrome patients are predisposed to different cancers in a non-random fashion, the basis of which is poorly understood. We addressed this issue by determining the molecular profiles for different tumors from a nationwide cohort of Lynch syndrome families (approximately 150 tumors in total). We focused on some less prevalent cancers, affecting the brain (n = 7) and urinary tract (five bladder and five ureter uroepithelial cancers and four kidney adenocarcinomas), and compared their molecular characteristics to those of the most common cancers, colorectal, gastric and endometrial adenocarcinomas, from the same families. Despite origin from verified MMR gene mutation carriers, the frequency of high-level microsatellite instability in tumors varied between high (100-96% for ureter, stomach and colon), intermediate (63-60% for endometrium and bladder) and low (25-0% for kidney and brain). In contrast to gastrointestinal and endometrial carcinomas, active (nuclear) beta-catenin was rare and KRAS mutations were absent in brain and urological tumors. Compared with other tumors, frequent stabilization of p53 protein characterized urinary tract cancers. Promoter methylation of tumor suppressor genes discriminated the tumors in an organ-specific manner. Our findings suggest that different Lynch syndrome tumors develop along different routes. Uroepithelial cancers of the ureter (and bladder to lesser extent) share many characteristics of MMR deficiency-driven tumorigenesis, whereas brain tumors and kidney adenocarcinomas follow separate pathways.