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Appl. Environ. Microbiol. doi:10.1128/AEM.01495-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Multiple-Locus Sequence Typing and analysis of Toxin genes of Bacillus cereus Foodborne Isolates

Department of Public Health, Comparative Pathology and Veterinary Hygiene, University of Padova, Agripolis, Viale dell'Università 16, 35020 Legnaro, Italy

^* To whom correspondence should be addressed. Email: barbara.cardazzo{at}unipd.it.

	Abstract

In the present study we characterized 47 foodborne isolates of Bacillus cereus using multi-locus sequence typing (MLST). Newly determined sequences were combined with sequences available in public data banks in order to produce the largest data set possible. Phylogenetic analysis was performed on a total of 296 strains for which MLST sequence information is available, and three main lineages I, II, III within the B. cereus complex were identified. With few exceptions, all foodborne isolates were in group I. The occurrence of horizontal gene transfer (HGT) among various strains was analyzed by several statistical methods providing evidence of widespread lateral gene transfer within B. cereus. We also investigated the occurrence of toxin-encoding genes, focusing on their evolutionary history within B. cereus. Several patterns were identified, indicating a pivotal role of horizontal gene transfer in the evolution of toxin-encoding genes. Our results indicate that horizontal gene transfer is an important element in shaping the population structure of the B. cereus complex. Results presented in this paper also provide strong evidence of reticulate evolution within the B. cereus complex.