Prevalence, virulence genes, and genetic diversity of Bacillus cereus isolated from convenience food.

BACKGROUND: In times when there is a growing interest in ready-to-eat food (RTEF), the presence of potentially pathogenic bacteria, including the toxigenic psychrotolerant bacilli from the B. cereus group, on this type of carrier may pose a real threat to the health of consumers. A significant part of RTEF is represented by vegetable products and food products made with them. The increased production of convenience foods has resulted in their international turnover growing. When coupled with a rising percentage of persons from risk groups (YOPI), including the elderly or immunocompromised, this may mean increased health risks posed by the so-called "novel pathogens", like the toxigenic psychrotolerant B. cereus sensu lato. METHODS: Food samples were analyzed for the presence and count of putative B. cereus according to the Polish Standard PN-EN ISO 7932:2005. All genetic analyses were conducted using a qualitative real-time PCR. RESULTS: The presence of B. cereus sensu lato was confirmed in 130 out of the 192 samples of convenience foods, at contamination levels ranging from 1.65 to 3.32 log CFU/g. Among the strains confirmed to belong to the B. cereus group, 23 were identified as emetic B. cereus. The analysis of each strain's ability to grow at temp. 4-10°C demonstrated that 4.9% and 12.7% of the isolates were able to grow at 4°C and 6°C, respectively. In turn, 15.2% were able to grow at 8°C, and 36.3% at 10°C. None of the psychrotrophic strains possessed genes typical of B. weihenstephanensis. The group of psychrotrophic B. cereus included potentially toxigenic strains being carriers of genes that determine the synthesis of the following toxins: NHE, HBL, CytK, and cereulide. Some of them were potent enough to produce more than one toxin. CONCLUSIONS: The analyses conducted in this study demonstrate that the psychrotolerant strains of B. cereus (including the toxigenic ones) are frequent microbiological contaminants of RTEF products offered in retail. The presence of emetic strains from the B. cereus group, which are able to grow in a wide range of temperatures and produce enterotoxins and enzymes with the characteristics of toxins, in ready-to-eat foods may pose a real threat to consumer health.

The possible effect of a sanitization program on intraspecies differentiation of Listeria monocytogenes strains isolated from a fish processing plant.

Forty-seven Listeria monocytogenes strains isolated during a year in a selected Polish fish-processing plant as well as 7 L. monocytogenes strains of different origins (including a reference strain) were analyzed in our studies. Strains were isolated from raw fish fillets (flounder), frozen coated flounder fillets, coating ingredients, and the processing environment. Isolation of strains covered the period of a sanitization program introduced in the plant. L. monocytogenes was identified using conventional microbiological methods and the PCR technique. RAPD (random amplified polymorphic DNA) technique for fingerprinting was applied to analyze the intraspecies diversity. Six RAPD types (A-F) and seven unique strains were revealed as a result of fingerprinting with one persistent type isolated from July 1999 to February 2000. It was detected for the first time after one month of sanitization. Its occurrence could have been promoted by clone selection either due to ineffective disinfection or to resistance against the disinfectant. As L. monocytogenes mostly occurred on frozen products, this indicates that contamination could start during product freezing, cold storage, or handling. The results revealed that there is a crucial need for preparing sanitization schemes precisely targeted at L. monocytogenes to avoid its recurrence as persistent 'in-house' strains. The possibility of incorrect interpretations of classical microbiological test results as well as the necessity to introduce assays based on nucleic acid analysis into epidemiological investigations were emphasized.