Abstract
BackgroundVibrios, which include more than 100 species, are ubiquitous in marine and estuarine environments, and several of them e.g. Vibrio cholerae, V. parahaemolyticus, V. vulnificus and V. mimicus, are pathogens for humans. Pathogenic V. parahaemolyticus strains possess two sets of genes for type III secretion system (T3SS), T3SS1 and T3SS2. The latter are critical for virulence of the organism and be classified into two distinct phylogroups, T3SS2α and T3SS2β, which are reportedly also found in pathogenic V. cholerae non-O1/non-O139 serogroup strains. However, whether T3SS2-related genes are present in other Vibrio species remains unclear.ResultsWe therefore examined the distribution of the genes for T3SS2 in vibrios other than V. parahaemolyticus by using a PCR assay targeting both T3SS2α and T3SS2β genes. Among the 32 Vibrio species tested in our study, several T3SS2-related genes were detected in three species, V. cholerae, V. mimicus and V. hollisae, and most of the essential genes for type III secretion were present in T3SS2-positive V. cholerae and V. mimicus strains. Moreover, both V. mimicus strains possessing T3SS2α and T3SS2β were identified. The gene organization of the T3SS2 gene clusters in V. mimicus strains was fundamentally similar to that of V. parahaemolyticus and V. cholerae in both T3SS2α- and T3SS2β-possessing strains.ConclusionsThis study is the first reported evidence of the presence of T3SS2 gene clusters in V. mimicus strains. This finding thus provides a new insight into the pathogenicity of the V. mimicus species.
Highlights
Vibrios, which include more than 100 species, are ubiquitous in marine and estuarine environments, and several of them e.g. Vibrio cholerae, V. parahaemolyticus, V. vulnificus and V. mimicus, are pathogens for humans
Of the nine T3SS2-positive V. mimicus strains, eight were identified as T3SS2-positive V. mimicus strains RIMD2218080 (T3SS2a)-positive, and one as T3SS2b-positive. These findings suggest that, in addition to their distribution in V. parahaemolyticus and V. cholerae strains, the genes for T3SS2 are found in V. hollisae and V. mimicus strains, only three T3SS2 genes were detected in V. hollisae strains
The PCR product which was amplified between vopD2 and vopP was the same size as that of the V. parahaemolyticus TH3996 strain. This suggested that the gene organization of T3SS2 of V. mimicus RIMD2218067 is similar to that of T3SS2b of V. parahaemolyticus, while a genetic element of approximately 5 kb, which could not be detected in the region of V. parahaemolyticus strain TH3996, may exist in the region between the vopP and vopC genes in V. mimicus strain RIMD2218067. These findings suggest that the gene organization of the T3SS2 gene clusters, both T3SS2a and T3SS2b, in V. mimicus strains are basically similar to those of the V. parahaemolyticus and V. cholerae strains
Summary
Vibrios, which include more than 100 species, are ubiquitous in marine and estuarine environments, and several of them e.g. Vibrio cholerae, V. parahaemolyticus, V. vulnificus and V. mimicus, are pathogens for humans. Pathogenic V. parahaemolyticus strains possess two sets of genes for type III secretion system (T3SS), T3SS1 and T3SS2. The latter are critical for virulence of the organism and be classified into two distinct phylogroups, T3SS2a and T3SS2b, which are reportedly found in pathogenic V. cholerae non-O1/non-O139 serogroup strains. The type III secretion system (T3SS) is possessed by gram-negative bacteria, especially those occurring in animal and plant pathogens, e.g. Yersinia, Shigella, Salmonella, Pseudomonas and Escherichia species [1,2,3]. Genome sequencing of the KP-positive V. parahaemolyticus strain RIMD2210633 demonstrated that it possesses two sets of the genes for T3SS on chromosomes 1 and 2 (T3SS1 and T3SS2, respectively) [7]. The T3SS2 genes are located on a pathogenicity island (PAI) known as Vp-PAI on chromosome 2, and the genes were found in KP-positive, but not in KP-negative strains [7,14,15]
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