Genetic diversity of emetic toxin producing Bacillus cereus Korean strains

Genotypic Profiling of Bacillus cereus Recovered from Some Retail Foods in Ogun State, Nigeria, and Their Phylogenetic Relationship

Identifying Bacillus cereus with conventional methods is neither specific nor rapid because of the close relatedness of the B. cereus group, hence the need for molecular methods. Genotypic profiling of B. cereus isolates from food was obtained by Random Amplified Polymorphic DNA-polymerase chain reaction (RAPD-PCR) using OPR13 primer. A dendrogram was drawn with the Numerical Taxonomy System of Statistic (NTSYS) software. Thirty of the isolates were subjected to molecular identification by 16S rDNA sequencing. The thirty sequences were deposited in GenBank for accession number. Phylogenetic relationship of the 16S rDNA sequence obtained was carried out with the Multiple Alignment using Fast Fourier Transform (MAFFT) software version 7.0. The evolutionary tree was drawn using the Molecular Evolutionary Genetics Analysis (MEGA 6) software. The dendrogram generated for the RAPD profile showed that all the strains are closely related, with a similarity coefficient of 70%. The isolates were confirmed with 16S rDNA sequencing as B. cereus. The thirty sequences deposited in GenBank were given accession numbers: KX574760–KX574769, KX610811–KX610820, MT757957-MT757963, and MT772282-MT772284. By comparing the phylogenetic relationship, eleven of the strains did not cluster with the reference strains from the GenBank but form distinct clades, which means they are likely to be of different ancestors. Conventional methods rarely differentiate bacteria of the same species into clade, neither can it describe their ancestral lineage. Therefore, it is important to employ molecular methods in identifying bacteria to give detailed information about them.

Enterotoxin and Emetic Toxin Genes Profiles and Genetic Diversity of Bacillus cereus Isolated from Food, Environmental and Clinical Samples in Serbia

Bacillus cereus, usually ingested by food, can cause two types of disease due to the presence of toxins: vomiting and diarrhea syndrome. Systemic infections can also occur. The aim was to detect genes for enterotoxins (hblA, entFM) and emetic toxin (cer) and to investigate the genetic heterogeneity of B. cereus isolates from food, environment and human stool. Identification of B. cereus was performed by means of selective medium, classical biochemical test and polymerase chain reaction (PCR). Toxin genes were detected by PCR. Typing was performed by random amplified polymorphic DNA (RAPD). EntFM gene was present in all stool and food samples and in 28/30 environmental isolates. HblA gene was present in 29/30 stool, 23/30 food and 24/30 environmental isolates. Cer gene was present in 30/30 stool, 28/30 food and 25/30 environmental isolates. The RAPD results show high heterogeneity among the isolates from each group. In the cumulative dendrogram, representative isolates from all three groups formed two clusters with a difference of 53%. The detection of toxin genes in all B. cereus isolates indicated these bacteria as potentially pathogenic and a serious threat for human health. The presence of isolates from all three groups in the same cluster suggests the existence of similar strains in the environment, food and patients, which is in line with the circulation of strains in nature through the food chain.

Genotypic heterogeneity of emetic toxin producing Bacillus cereus isolates from China

Emetic toxin-producing Bacillus cereus (emetic B. cereus) is the third member of B. cereus group whose toxins are encoded by megaplasmids, beside anthrax and insecticidal toxins of B. anthracis and B. thuringiensis, respectively. A total of 18 emetic isolates collected from food poisoning events, clinical and non-random food samples in Zhejiang province of China, were analyzed by plasmid screening, pulse field gel electrophoresis, multilocus sequence typing, and toxic gene identification to investigate their genotypic diversity. In this study, 13 plasmid profile types, 14 pulse types and 6 different STs from emetic isolates were detected, in which ST 1035,1038,1053,1054 and 1065 were first assigned and reported. The toxic gene ces existed on its own, or coexisted with other toxic genes bceT, cytk, entFM and nhe, but never with hbl in emetic isolates. The results demonstrated that the emetic B. cereus strains from China were heterologous at genotypic level.

Diversity of pulsed-field gel electrophoresis patterns of cereulide-producing isolates of Bacillus cereus and Bacillus weihenstephanensis

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.

Differentiation of strains from the Bacillus cereus group by RFLP-PFGE genomic fingerprinting

Bacillus mycoides, Bacillus pseudomycoides, Bacillus weihenstephanensis, Bacillus anthracis, Bacillus thuringiensis, and Bacillus cereus belong to the B. cereus group. The last three species are characterized by different phenotype features and pathogenicity spectrum, but it has been shown that these species are genetically closely related. The macrorestriction analysis of the genomic DNA with the NotI enzyme was used to generate polymorphism of restriction profiles for 39 food-borne isolates (B. cereus, B. mycoides) and seven reference strains (B. mycoides, B. thuringiensis, B. weihenstephanensis, and B. cereus). The PFGE method was applied to differentiate the examined strains of the B. cereus group. On the basis of the unweighted pair group method with the arithmetic mean method and Dice coefficient, the strains were divided into five clusters (types A-E), and the most numerous group was group A (25 strains). A total of 21 distinct pulsotypes were observed. The RFLP-PFGE analysis was successfully used for the differentiation and characterization of B. cereus and B. mycoides strains isolated from different food products.