RESUMO
Bacillus cereus is an important foodborne pathogen causing diarrhoea, emesis and in, rare cases, lethal poisonings. The emetic syndrome is caused by cereulide, a heat-stable toxin. Originally considered as a rather homogenous group, the emetic strains have since been shown to display some diversity, including the existence of two clusters of mesophilic B. cereus and psychrotolerant B. weihenstephanensis. Using pulsed-field gel electrophoresis (PFGE) analysis, this research aimed to better understand the diversity and spatio-temporal occurrence of emetic strains originating from environmental or food niches vs. those isolated from foodborne cases. The diversity was evaluated using a set of 52 B. cereus and B. weihenstephanensis strains isolated between 2000 and 2011 in ten countries. PFGE analysis could discriminate 17 distinct profiles (pulsotypes). The most striking observations were as follows: (1) more than one emetic pulsotype can be observed in a single outbreak; (2) the number of distinct isolates involved in emetic intoxications is limited, and these potentially clonal strains frequently occurred in successive and independent food poisoning cases; (3) isolates from different countries displayed identical profiles; and (4) the cereulide-producing psychrotolerant B. weihenstephanensis were, so far, only isolated from environmental niches.
Assuntos
Bacillus/genética , Depsipeptídeos/metabolismo , Variação Genética , Genoma Bacteriano/genética , Bacillus/classificação , Bacillus/metabolismo , Bacillus cereus/classificação , Bacillus cereus/genética , Bacillus cereus/metabolismo , Técnicas de Tipagem Bacteriana , Eletroforese em Gel de Campo Pulsado , Eméticos , Microbiologia Ambiental , Microbiologia de Alimentos , Doenças Transmitidas por Alimentos/microbiologia , Humanos , Análise Espaço-TemporalRESUMO
Two thousand Bacillus cereus sensu lato isolates from food and environmental matrices were screened by PCR for the presence of cereulide-producing strains. This survey identified 73 potential emetic strains, most of which originated from non-random food and clinical samplings. None of the 460 Bacillus thuringiensis, Bacillus mycoides and Bacillus pseudomycoides strains were PCR-positive for the cereulide genetic determinants. The chromosomal and extrachromosomal gene pool diversity of a subset of 30 cereulide-producing strains was then assessed using multilocus sequence typing, large plasmid gel electrophoresis and Southern blot hybridization. The strain toxicity on boar sperm and cereulide production were also analysed. The most striking observation was the identification of two distinct clusters of cereulide-producing strains, with members of the second group (cluster II) identified as psychrotolerant B. weihenstephanensis able to grow at 8°C. Moreover, the location of the cereulide genetic determinants was shown to vary depending on the strain, indicating a probable genomic mobility.