B-198. Arrangement of Mannitol Genes as an Indicator of Virulence in C-Genotype Strains of Vibrio vulnificus
Vibrio vulnificus, an estuarine bacterium, causes food-borne and wound infections. Nearly 95% of all seafood-borne deaths are caused by this organism, usually following consumption of raw or undercooked oysters. Based on FDA estimates of the number of Americans with conditions that predispose to V. vulnificus infection, there should be far more cases than the ca. 50 that are reported each year. This lab recently reported (Rosche et al., 2005. Microbiol. Immunol. 49:381-389) that V. vulnificus could be subdivided into two genotypes: a “C-type” where 90% correspond to clinical isolates and an “E-type” corresponding 93% to environmental isolates. We subsequently reported (Warner and Oliver, Appl. Environ. Microbiol. 74 80-85) that only 13% of oyster isolates are of the C-type. Nevertheless, such a disproportionately low level of the virulent form in oysters cannot solely account for the number of susceptible individuals vs. the small number of actual cases. In a study of 121 C- and E-type isolates of V. vulnificus, we found that 100% of C-type but only 40% of E-type strains ferment mannitol. An examination of the relevant genes indicated that their arrangement, as well as the arrangement of two additional upstream genes, could be employed to further subdivide C-type strains according to their potential pathogenicity. Of 33 V. vulnificus strains in which gene arrangement was studied, those strains that were unable to ferment mannitol were also lacking the three conserved genes normally associated with this hexitol. All 33 strains, regardless of fermentative ability, were found to contain a putative hemolysin gene and a TRAP-type mannitol transport gene. Interestingly, PCR analysis revealed both of these genes in clinically isolated C-type strains were adjacent and immediately upstream of the mannitol fermentation genes. E-type strains, while possessing both genes, have them located elsewhere and not adjacent in the chromosome. Only 57% of C-type stains isolated from the environment showed a similar arrangement to the clinical isolates. Thus, PCR analysis of these specific genes can possibly be used to identify potentially pathogenic strains.