Ecological diversity of cereulide-producing strains of Bacillus cereus and Bacillus weihenstephanensis
(2012) Balgian Society for Applied Microbiology — Location: Brussels (20.September.2012)
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- Bacillus weihenstephanensis Virginie Castiaux1, Izabela Swiecicka2 and Jacques Mahillon1 1Laboratory of Food and Environmental Microbiology, Earth and Life Institute, UCL, Croix du Sud 2 - L7.05.12, B-1348 Louvain-la-Neuve, Belgium. 2Department of Microbiology, Institute of Biology, University of Bialystock, 20B Swierkowa Street, PL15-950 Bialystock, Poland. Background and aims Bacillus cereus is an important foodborne pathogen causing diarrhea or emesis and even lethal poisoning (1). The emetic syndrome is caused by the production of a heat-stable dodecadepsipeptide toxin, the cereulide. Cereulide-producing strains of B. cereus are known to be a group of closely related strains. The aim of this work was to study the diversity of these strains in food and environmental niches and to gather more insights into the ecology and epidemiology of these strains. Methods A set of fifty-two cereulide-producing strains was used in this study. They were isolated from foods, emetic-type food poisoning cases and environmental niches (soil, mammals and rodents), as previously described by Hoton and coll. (2009) (2). They originated from ten countries (Belgium, China, Denmark, France, Germany, Ivory Coast, Poland, Switzerland, United Kingdom and Unites States) and were isolated, in majority, between 2003 and 2011. The genotypic and phenotypic characteristics of these strains were studied using biochemical tests (API20E and API50CH) and molecular methods (Pulsed Field Gel Electrophoresis, PFGE). Results The phenotypic study confirmed the existence of two distinct clusters among emetic strains. Indeed, the majority of strains were unable to degrade starch and glycogen (Cluster I) while members of the cluster II were positive. The diversity within the emetic strains was also assessed by comparing their lecithinase and haemolysis activities. All the strains were positive for these two tests except three strains. These phenotypic traits are important since the key diagnostic features of B. cereus are based on these activities. In routine detection, these pathogens strains cannot be considered as B. cereus and this can lead to misidentification and underestimation of foodborne illnesses caused by these bacteria. The characterization by PFGE could discriminate 17 different profiles from a total of 52 strains analyzed. Several striking observations could be made from these results. First, emetic strains isolated from the same outbreak in different matrices gave rise to different pulsotypes. Secondly, the number of strains involved in food intoxications is limited and this group of clonal (or undistinguishable by PFGE) strains frequently occurred in successive outbreaks. Finally, the pulsotyping of random isolates from different countries (geographically remote) displayed the same profile. For instance, Belgian food emetic strains were found to share the same profile with two Chinese strains isolated from ice creams. Conclusions Taken together, these data demonstrate the importance to perform a systematic characterization of all emetic strains by PFGE. This is essential for further epidemiological studies and to gather important information on their potential reservoirs. References 1. Naranjo M., Denayer S., Botteldoorn N., Delbrassinne L., Veys J., Waegenaere J., Sirtaine N., Driesen R. B., Sipido K. R., Mahillon J. and Dierick K. (2011) Sudden death of a young adult associated with Bacillus cereus food poisoning. J. Clin. Microbiol. 49: 4379-81. 2. Hoton, F. M., Fornelos, N., N’Guessan, E., Hu, X., Swiecicka, I., Dierick, K., et al. (2009) Family portrait of Bacillus cereus and Bacillus weihenstephanensis cereulide-producing strains. Env. Microbiol. Rep. 1, 177-183.
Citations
Castiaux, V., Mahillon, J., & et al. (2012). Ecological diversity of cereulide-producing strains of Bacillus cereus and Bacillus weihenstephanensis. Balgian Society for Applied Microbiology, Brussels. https://hdl.handle.net/2078.5/45775