Detection of potentially enterotoxigenic food-related Bacillus cereus by PCR analysis

Prevalence, Virulence Potential, and Growth in Cheese of Bacillus cereus Strains Isolated from Fresh and Short-Ripened Cheeses Sold on the Italian Market

This study investigated B. cereus presence in 122 samples belonging to 34 typologies of fresh or short-ripened cheeses made from cow, sheep, goat, or buffalo pasteurized milk, and sold on the Italian market. B. cereus was isolated at a prevalence of 9.8%, with a marked variability among cheese categories, and at low counts (always below 2.26 Log CFU/g). Twelve isolates were identified by MALDI-TOF analysis and typified by RAPD PCR as belonging to different B. cereus strains. All the strains were tested for the production of hemolysin BL, phosphatidylcholine-specific phospholipase C, proteases, and biofilm formation, and for the presence of chromosomal toxin-encoding genes (sph, plcA, cytK, entFM, bcet, nheA, nheB, nheC). Overall, 92% of strains harbored bcet, 75% the three genes nheA, nheB, and nheC, as well as plcA and sph, 67% entFM, and 33% cytK. All strains showed biofilm-forming ability. A chemical-physical characterization of the cheeses was also performed to show their suitability as substrates for B. cereus growth, showing high heterogeneity in terms of pH, aw, salt content, and concentration of organic acids. Finally, the ability to support spore germination and vegetative cell growth of a selected cheese was investigated in spores-inoculated samples maintained at 10 °C and 15 °C, showing the inhibitory effect of low storage temperatures.

Toxigenic Potential of Mesophilic and Psychrotolerant Bacillus cereus Isolates from Chilled Tofu

The prevalence, toxin gene profile, antibiogram, and biofilm formation to determine the virulence potential of mesophilic and psychrotolerant Bacillus cereus (B. cereus) isolated from chilled tofu were investigated. Among 58 isolates, 21 isolates were capable of growth at 7 °C, and these isolates shared a potential hazard for food poisoning with mesophilic isolates. B. cereus harboring enterotoxin genes was more frequently found in psychrotolerant isolates than in mesophilic isolates. Thirty-seven (62.2%) mesophilic isolates and all psychrotolerant isolates carried four or more enterotoxin genes. The hemolysin BL (42.9%) and nonhemolytic enterotoxin complexes (90.5%) were found at a higher frequency in psychrotolerant isolates than in mesophilic isolates. Some B. cereus isolates showed resistance to rifampicin or clindamycin, regardless of mesophilic and psychrotolerant isolates. A total of 56% and 40% mesophilic isolates displayed the strongest biofilm formation at 40 and 42 °C, respectively. However, the biofilm formation of psychrotolerant isolates was not significantly affected by temperature. The results of this study provide new strategies for the development of bacterial control, which allows us to optimize technologies to inhibit B. cereus, including psychrotolerant isolates, in the food industry.

Species-Specific Gene, spt5, in the Qualitative and Quantitative Detection of Boletus reticulatus

Boletus reticulatus is a wild edible fungus with high nutritional value in Yunnan Province. In this study, B. reticulatus was used as the research object to diagnose the species characteristics. A commercial kit was used to extract the DNA of various fungi, and the quality of DNA was determined by using universal fungus primers. Through sequence alignment, the spt5 gene was selected as the species-specific gene of B. reticulatus. This gene was then qualitatively and quantitatively analyzed by PCR. In the qualitative detection, the spt5 amplification products were only found in B. reticulatus which proved its good specificity. Meanwhile, SYBR Green I based quantitative PCR results were highly sensitive, and the limit of detection was 0.04 ng of genomic DNA. These experiments illustrated that spt5 is an ideal species-specific gene for the quantitative and qualitative detection of B. reticulatus. This method is also suitable for the analysis of the processed samples of B. reticulatus and the determination of the adulteration of edible wild mushrooms.

Exposure to Bacillus cereus in Water Buffalo Mozzarella Cheese

Bacillus cereus is a spoilage bacterium and is recognized as an agent of food poisoning. Two food-borne illnesses are caused by B. cereus: a diarrheal disease, associated with cytotoxin K, hemolysin BL, non-hemolytic enterotoxin and enterotoxin FM, and an emetic syndrome, associated with the cereulide toxin. Owing to the heat resistance of B. cereus and its ability to grow in milk, this organism should be considered potentially hazardous in dairy products. The present study assessed the risk of B. cereus poisoning due to the consumption of water buffalo mozzarella cheese. A total of 340 samples were analyzed to determine B. cereus counts (ISO 7932:2005); isolates underwent molecular characterization to detect the presence of genes encoding toxins. Eighty-nine (26.1%) samples harbored B. cereus strains, with values ranging from 2.2 × 102 to 2.6 × 106 CFU/g. Isolates showed eight different molecular profiles, and some displayed virulence characteristics. Bacterial counts and the toxin profiles of isolates were evaluated both separately and jointly to assess the risk of enteritis due to B. cereus following the consumption of buffalo mozzarella cheese. In conclusion, the results of the present study showed that the risk of poisoning by B. cereus following the consumption of this cheese was moderate.

A Study on Prevalence and Characterization of Bacillus cereus in Ready-to-Eat Foods in China

Bacillus cereus is widely distributed in different food products and can cause a variety of symptoms associated with food poisoning. Since ready-to-eat (RTE) foods are not commonly sterilized by heat treatment before consumption, B. cereus contamination may cause severe food safety problems. In this study, we investigated the prevalence of B. cereus in RTE food samples from different regions of China and evaluated the levels of bacterial contamination, antibiotic resistance, virulence gene distribution, and genetic polymorphisms of these isolates. Of the tested retail RTE foods, 35% were positive for B. cereus, with 39 and 83% of the isolated strains harboring the enterotoxin-encoding hblACD and nheABC gene clusters, respectively. The entFM gene was detected in all B. cereus strains. The cytK gene was present in 68% of isolates, but only 7% harbored the emetic toxin-encoding gene cesB. Antimicrobial susceptibility testing revealed that the majority of the isolates were resistant not only to most β-lactam antibiotics, but also to rifamycin. Multilocus sequence typing (MLST) revealed that the 368 isolates belonged to 192 different sequence types (STs) including 93 new STs, the most prevalent of which was ST26. Collectively, our study indicates the prevalence, bacterial contamination levels, and biological characteristics of B. cereus isolated from RTE foods in China and demonstrates the potential hazards of B. cereus in RTE foods.

Toxigenic potential and antimicrobial susceptibility of Bacillus cereus group bacteria isolated from Tunisian foodstuffs

BACKGROUND

Despite the importance of the B. cereus group as major foodborne pathogens that may cause diarrheal and/or emetic syndrome(s), no study in Tunisia has been conducted in order to characterize the pathogenic potential of the B. cereus group. The aim of this study was to assess the sanitary potential risks of 174 B. cereus group strains isolated from different foodstuffs by detecting and profiling virulence genes (hblA, hblB, hblC, hblD, nheA, nheB, nheC, cytK, bceT and ces), testing the isolates cytotoxic activity on Caco-2 cells and antimicrobial susceptibility towards 11 antibiotics.

RESULTS

The entertoxin genes detected among B. cereus isolates were, in decreasing order, nheA (98.9%), nheC (97.7%) and nheB (86.8%) versus hblC (54.6%), hblD (54.6%), hblA (29.9%) and hblB (14.9%), respectively encoding for Non-hemolytic enterotoxin (NHE) and Hemolysin BL (HBL). The isolates are multi-toxigenic, harbouring at least one gene of each NHE and HBL complexes associated or not to bceT, cytK-2 and ces genes. Based on the incidence of virulence genes, the strains were separated into 12 toxigenic groups. Isolates positive for cytK (37,9%) harbored the cytK-2 variant. The detection rates of bceT and ces genes were 50.6 and 4%, respectively. When bacteria were incubated in BHI-YE at 30 °C for 18 h and for 5 d, 70.7 and 35% of the strains were shown to be cytotoxic to Caco-2 cells, respectively. The cytotoxicity of B. cereus strains depended on the food source of isolation. The presence of virulence factors is not always consistent with cytotoxicity. However, different combinations of enterotoxin genetic determinants are significantly associated to the cytotoxic potential of the bacteria. All strains were fully sensitive to rifampicin, chloramphenicol, ciprofloxacin, and gentamycin. The majority of the isolates were susceptible to streptomycin, kanamycin, erythromycin, vancomycin and tetracycline but showed resistance to ampicillin and novobiocin.

CONCLUSION

Our results contribute data that are primary to facilitate risk assessments in order to prevent food poisoning due to B. cereus group.

Isolation of Bacillus cereus Group from the Fecal Material of Endangered Wood Turtles

Members of the Bacillus cereus group are opportunistic human pathogens. They can be found in a broad range of foods. Diarrheal food poisoning and/or emetic type syndromes can result from eating contaminated food. In this study, seven B. cereus group members were isolated from the fecal material of Wood Turtles (Glyptemys insculpta). The isolates were then assessed for the presence of enterotoxin genes (nheA, entFM, hblC, and cytK) using PCR. The most prevalent is the nonhemolytic enterotoxin gene which was found in all seven isolates.

Regulation of toxin production by Bacillus cereus and its food safety implications

Toxin expression is of utmost importance for the food-borne pathogen B. cereus, both in food poisoning and non-gastrointestinal host infections as well as in interbacterial competition. Therefore it is no surprise that the toxin gene expression is tightly regulated by various internal and environmental signals. An overview of the current knowledge regarding emetic and diarrheal toxin transcription and expression is presented in this review. The food safety aspects and management tools such as temperature control, food preservatives and modified atmosphere packaging are discussed specifically for B. cereus emetic and diarrheal toxin production.