Distribution of Virulence‐Associated Genes in Vibrio mimicus Isolates from Clinical and Environmental Origins

Abstract

The genus Vibrio contains some enteropathogenic species including V. cholerae, V. parahaemolyticus, V. fluvialis and V. mimicus. V. cholerae is responsible for severe cholera epidemics in many parts of the world, especially developing countries (4,12). V. mimicus has been recognized as a biotype of V. cholerae, but was reclassified as an independent species because of differences in some biochemical characteristics including negative sucrose fermentation in 1981 (5). Therefore V. mimicus and V. cholerae are quite similar to each other and they share some pathogenic factors such as enterotoxins or hemolysins (15,19,24). Although V. mimicus has not been reported to produce severe epidemic of diarrhea like V. cholerae, it is often isolated from patients of sporadic diarrheal cases (14).Successful infection by pathogenic bacteria is established by coordinate expression of various virulence factors in addition to actual toxic factors. In V. cholerae, ToxR ToxS, ToxT and toxin co-regulated pilus (TCP) are known to coordinate the action of the major toxic factor, cholera toxin (CT) (8,13,21). Production of these virulence factors is regulated at the transcriptional level by ToxR (6, 7). Meanwhile, ToxS is known to enhance ToxR-mediated transcriptional activation (10). Moreover, ToxR is conjugated with another transmembrane transcriptional activator, and TcpP positively controls the expression of ToxT (6, 9). ToxT can directly activate expression of the genes encoding CT, TCP (21) and other virulence determinants (6, 7). TCP, the product of the tcpA gene, plays an important role in the colonization of V. cholerae O1/O139, and also acts as a receptor for the acquisition of the CTXΦ genetic element (23). Recent studies have demonstrated the presence of the tcpA gene, as well as the ctxA gene encoding CT, in certain non-O1/non-O139 V. cholerae strains (8,14). A hypothesis on horizontal transfer of the virulence genes among Vibrio species has been proposed (23). Distribution of these virulence-associated genetical elements in V. mimicus is also possible because of its taxonomical relatedness with V. cholerae (3).We have surveyed the existence of virulence-associated genes by the polymerase chain reaction (PCR) method (2,15,16 Shinjuku-ku, Tokyo 162-8640, Japan Received February 23, 2004. Accepted April 13, 2004 Abstract: Distribution of virulence-associated genes in Vibrio mimicus was studied including the toxin genes ctxA, tdh, st and vmh and the genes necessary for regulation of toxin production, toxR, toxS, toxT, tcpA and tcpP. Approximately half of clinical V. mimicus isolates possessed one or more genes encoding V. cholerae enterotoxic factors such as ctxA, tdh and st. All of the clinical and environmental isolates possessed vmh encoding V. mimicus hemolysin (VMH). The ctxA encoding cholera toxin was detected in only 2 strains, 5% of the clinical isolates. Furthermore, there were very few strains possessing tcpP and toxT needed for the expression of ctxA. These results may suggest that VMH is a more important pathog...

Distribution of five vibrio virulence-related genes among Vibrio harveyi isolates

“…The plasmids were transformed into E. coli JM109 competent cells, and the sequence of the cloned genes in the vector pMD 18-T was confirmed by DNA sequencing (Invitrogen Biotech, Shanghai, China). Previous studies have shown the distribution of different virulence genes among V. cholerae, V. mimicus, V. alginolyticus and V. parahaemolyticus (Ghosh et al, 1997;Sechi et al, 2000;Shi et al, 1998;Shinoda and Nakagawa, 2004;Xie et al, 2005). Our results indicate that the virulence genes such as toxS, flaB and flaC are widely distributed among different vibrios, whereas zot and tcpA only exit in a few vibrios.…”

“…It was also found to be present in V. 74 Vol. 54 BAI et al alginolyticus (Sechi et al, 2000) and V. mimicus (Shinoda and Nakagawa, 2004). In comparison, zot and tcpA did not exist in any of the 30 V. harveyi isolates tested.…”

“…The toxS gene of V. harveyi VIB400 and VIB649 are 83% identical to the V. parahaemolyticus toxR and toxS genes. Sechi et al (2000) found that most Vibrio strains (73.58%) could amplify the expected band and Shinoda and Nakagawa (2004) elucidated that 97% of the tested V. mimicus include the toxS gene. However, our results showed that 23% of Vibrio type strains gave a positive result, and only 16% of V. harveyi amplified the expected band.…”

“…These results coincide with previous findings that zot and tcpA were very rare in other Vibrio species, although they were very important to V. cholerae. It is apparent that these genes may be obtained by the horizontal transfer (Shinoda and Nakagawa, 2004).…”

Role of the Enterotoxic Hemolysin in Pathogenicity of Vibrio mimicus

“…okayama-u.ac.jp of a virulence determinant. For instance, Shinoda et al 5) documented that the gene encoding VMH, but not other toxins, is present in all strains isolated from various clinical and environmental specimens. VMH is secreted from the bacterial cell as an 80-kDa (80399 Da) precursor and, in turn, converted to a 66-kDa (65997 Da) mature form through proteolytic removal of a N-terminal propeptide.…”