Origin, prevalence and diversity of foodborne and environmental strains of Bacillus cytotoxicus

Bacillus cereus s.l. is soil dweller that gathers rode-shape Gram-positive, and spore forming bacteria. The group contains beneficial, non-pathogenic as well pathogenic species. From their natural environment, B. cereus contaminates food products and can cause two types of foodborne diseases: emetic and diarrhoeal syndromes. In 1998, a fatal diarrhoeal outbreak occurred in a nursing house in France. Bacillus cytotoxicus, a thermotolerant B. cereus, was isolated and shown to harbour cytK-1, a gene encoding the most cytotoxic variant of Cytotoxin K, one of the three prominent enterotoxins presumably responsible of the diarrhoeal syndrome. This thesis aimed at exploring the ecological niche of B. cytotoxicus, assessing its diversity and clarifying the role of CytK-1 toxin in B. cytotoxicus cytotoxicity. Our results support that B. cytotoxicus is rare in nature. Overall, 39 out of 339 (11,5%) food and environment samples were positive to B. cytotoxicus, with a high prevalence in potato flakes and potato derived products. From Malian foods though, B. cytotoxicus was also found in Millet flour for children and fish powder for the first time ever. A study case in a potato processing food-industry revealed that B. cytotoxicus and other thermotolerant B. cereus were positively selected by the industrial process. Band-based profiling (RAPD and plasmid profiling) of 57 strains showed six RAPD patterns and eleven plasmids profiles. SNPs computing revealed that strains with RAPD pattern A fitted in genomic clade C while those with pattern D clustered in clade D. Sole members of RAPD patterns E and F did not fit in any genomic clade. Inositol degradation and acetoin anabolism operons, and lactose uptake and utilisation coding genes were first ever reported in B. cytotoxicus. Prophages sequences and plasmid content played a role in genomic diversity the species. A mutant lacking in cytK-1 gene showed significantly decreased cytotoxicity. This indicates that CytK-1 is the main toxin responsible of B. cytotoxicus toxicity(AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 202

pXO16, the large conjugative plasmid from Bacillus thuringiensis serovar israelensis displays an extended host spectrum

pXO16, the large conjugative plasmid from Bacillus thuringiensis serovar israelensis is able to efficient self-transfer, to mobilize and retro-mobilize non-conjugative plasmids, including "non-mobilizable" plasmids, and to transfer chromosomal loci. It also displays a remarkable aggregation phenotype associated with conjugation under liquid conditions. However, it was recently shown that aggregation boosts pXO16 transfer but is not mandatory. In this paper, we have further explored pXO16 transfers under various mating conditions and with different members of the Bacillus cereus group. The results indicated that colony or filter mating largely compensate the transfer deficit observed when using a pXO16 aggregation-minus mutant. Using filter mating, pXO16 transfer efficiency and host range were both improved. For instance, pXO16 was shown to transfer itself, and to mobilize the small pUB110 plasmid, from B. thuringiensis serovar israelensis to the thermotolerant Bacillus cytotoxicus at frequencies of 3.3 × 10-3 and 5.2 × 10-4 transconjugants per donor (T/D), respectively. All together, these results indicate that pXO16 can potentially "circulate" among members of the Bacillus cereus group. Yet, this is contrasting with pXO16's known natural distribution, which is apparently limited to the israelensis serovar of B. thuringiensis

Prevalence and Diversity of the Thermotolerant Bacterium Bacillus cytotoxicus among Dried Food Products

Bacillus cytotoxicus, a member of the Bacillus cereus group, is a thermotolerant species originally reported from a lethal foodborne infection in France in 1998. The strain NVH391-98, isolated from this outbreak, produces cytotoxin K1, a potential cytotoxic enterotoxin. However, the habitat and diversity of B. cytotoxicus isolates so far have been poorly explored. The objective of this study was to assess the prevalence of this bacterium in different food products (mainly dried) and to estimate its diversity. Among the 210 samples analyzed, all potato flakes contained the bacterium at low concentrations (≤102 CFU/g). However, prepared and kept at room temperature for 2 days, the puree contained ca. 105 CFU/g B. cytotoxicus. Besides potato flakes, some samples of millet flour, salted potato chips, and soups also contained B. cytotoxicus. From these samples, 55 thermotolerant B. cytotoxicus isolates were obtained. When classified into six distinct random amplified polymorphism DNA patterns, they showed the existence of 11 distinct plasmid profiles. Although most isolates (including the reference strains NVH391-98 and NVH883-00) contained no detectable plasmid, some displayed one to three plasmids with sizes from ca. 8 to 90 kb. It also emerged from this study that a single food sample could contain B. cytotoxicus isolates with different genetic profiles