Article

Genetic diversity of the human pathogen Vibrio vulnificus: A new phylogroup

Department of Biotechnology and Food Engineering, Technion, Israel Institute of Technology, Haifa 32000, Israel.
International journal of food microbiology (Impact Factor: 3.08). 02/2012; 153(3):436-43. DOI: 10.1016/j.ijfoodmicro.2011.12.011
Source: PubMed

ABSTRACT

The biotype 3 group of the human pathogen Vibrio vulnificus emerged in Israel probably as a result of genome hybridization of two bacterial populations. We performed a genomic and phylogenetic study of V. vulnificus strains isolated from the environmental niche from which this group emerged - fish aquaculture in Israel. The genetic relationships and evolutionary aspects of 188 environmental and clinical isolates of the bacterium were studied by genomic typing. Genetic relations were determined based on variation at 12 variable number tandem repeat (VNTR, also termed SSR) loci. Analysis revealed a new cluster, in addition to the main groups of biotype 1& 2 and biotype 3. Similar grouping results were obtained with three different statistical approaches. Isolates forming this new cluster presented unclear biochemical profile nevertheless were not identified as biotype 1 or biotype 3. Further examination of representative strains by multilocus sequence typing (MLST) of 10 housekeeping genes and 5 conserved hypothetical genes supported the identification of this as yet undiscovered phylogroup (phenotypically diverse), termed clade A herein. This new clonal subgroup includes environmental as well as clinical isolates. The results highlight the fish aquaculture environment, and possibly man-made ecological niches as a whole, as a source for the emergence of new pathogenic strains.

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    • "However, the use of 'biotyping' in the taxonomy of VV is somewhat controversial. Recently, Broza[100]challenged the classification of VV strains by the biotype scheme because of the ambiguity of this scheme as observed by Biosca et al.[101]for indole-positive, eel-infecting VV strains. Although indole, ODC, and ONPG findings are certainly useful to some extent and are still widely used for taxonomic tests to differentiate sub-species groups of VV, we agree that classification systems of VV based on only three enzymatic reactions might not properly reflect the exquisite taxonomic patterns of VV. "
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    • "V. vulnificus colonies were PCR-amplified for detection of the vvh gene (Broza et al., 2007). V. vulnificus isolates were identified by biochemical tests as previously described (Broza et al., 2012). "
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    • "MLST of housekeeping genes together with antigenencoding genes successfully differentiated E. faecalis at the strain level, and showed a genetic relatedness among BVE (beta-lactamase + , vancomycin R , endocarditis) clinical isolates (Nallapareddy et al., 2002, 2005). MLST may be relied on additional sources of sequence variation, such as 'conserved hypothetical' genes, which were successfully used for strain typing of other bacterial species (Broza et al., 2012; Buhnik-Rosenblau et al., 2012). This cluster of genes with unknown function is predicted to be present in the genomes of all members of the same species, and different 'conserved hypothetical' genes may present various degrees of polymorphism among strains. "
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