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The hemolytic enterotoxin HBL is broadly distributed among species of the Bacillus cereus group.

ABSTRACT: The prevalence of the hemolytic enterotoxin complex HBL was determined in all species of the Bacillus cereus group with the exception of Bacillus anthracis. hblA, encoding the binding subunit B, was detected by PCR and Southern analysis and was confirmed by partial sequencing of 18 strains. The sequences formed two clusters, one including B. cereus and Bacillus thuringiensis strains and the other one consisting of Bacillus mycoides, Bacillus pseudomycoides, and Bacillus weihenstephanensis strains. From eight B. thuringiensis strains, the enterotoxin gene hblA could be amplified. Seven of them also expressed the complete HBL complex as determined with specific antibodies against the L(1), L(2), and B components. Eleven of 16 B. mycoides strains, all 3 B. pseudomyoides strains, 9 of 15 B. weihenstephanensis strains, and 10 of 23 B. cereus strains carried hblA. While HBL was not expressed in the B. pseudomycoides strains, the molecular assays were in accordance with the immunological assays for the majority of the remaining strains. In summary, the hemolytic enterotoxin HBL seems to be broadly distributed among strains of the B. cereus group and relates neither to a certain species nor to a specific environment. The consequences of this finding for food safety considerations need to be evaluated.

SUBMITTER: Pruss BM

PROVIDER: S-EPMC91741 | biostudies-literature | 1999 Dec

REPOSITORIES: biostudies-literature

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The hemolytic enterotoxin HBL is broadly distributed among species of the Bacillus cereus group.

Prüss B M BM Dietrich R R Nibler B B Märtlbauer E E Scherer S S

Applied and environmental microbiology 19991201 12

The prevalence of the hemolytic enterotoxin complex HBL was determined in all species of the Bacillus cereus group with the exception of Bacillus anthracis. hblA, encoding the binding subunit B, was detected by PCR and Southern analysis and was confirmed by partial sequencing of 18 strains. The sequences formed two clusters, one including B. cereus and Bacillus thuringiensis strains and the other one consisting of Bacillus mycoides, Bacillus pseudomycoides, and Bacillus weihenstephanensis strain ...[more]

PMID: 10584001

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Project description:Bacillus cereus is a food contaminant with greatly varying enteropathogenic potential. Almost all known strains harbor the genes for at least one of the three enterotoxins Nhe, Hbl, and CytK. While some strains show no cytotoxicity, others have caused outbreaks, in rare cases even with lethal outcome. The reason for these differences in cytotoxicity is unknown. To gain insight into the origin of enterotoxin expression heterogeneity in different strains, the architecture and role of 5' intergenic regions (5' IGRs) upstream of the nhe and hbl operons was investigated. In silico comparison of 142 strains of all seven phylogenetic groups of B. cereus sensu lato proved the presence of long 5' IGRs upstream of the nheABC and hblCDAB operons, which harbor recognition sites for several transcriptional regulators, including the virulence regulator PlcR, redox regulators ResD and Fnr, the nutrient-sensitive regulator CodY as well as the master regulator for biofilm formation SinR. By determining transcription start sites, unusually long 5' untranslated regions (5' UTRs) upstream of the nhe and hbl start codons were identified, which are not present upstream of cytK-1 and cytK-2. Promoter fusions lacking various parts of the nhe and hbl 5' UTR in B. cereus INRA C3 showed that the entire 331 bp 5' UTR of nhe is necessary for full promoter activity, while the presence of the complete 606 bp hbl 5' UTR lowers promoter activity. Repression was caused by a 268 bp sequence directly upstream of the hbl transcription start. Luciferase activity of reporter strains containing nhe and hbl 5' IGR lux fusions provided evidence that toxin gene transcription is upregulated by the depletion of free amino acids. Electrophoretic mobility shift assays showed that the branched-chain amino acid sensing regulator CodY binds to both nhe and hbl 5' UTR downstream of the promoter, potentially acting as a nutrient-responsive roadblock repressor of toxin gene transcription. PlcR binding sites are highly conserved among all B. cereus sensu lato strains, indicating that this regulator does not significantly contribute to the heterogeneity in virulence potentials. The CodY recognition sites are far less conserved, perhaps conferring varying strengths of CodY binding, which might modulate toxin synthesis in a strain-specific manner.

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The hemolytic enterotoxin HBL is broadly distributed among species of the Bacillus cereus group.

Publications

The hemolytic enterotoxin HBL is broadly distributed among species of the Bacillus cereus group.

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