DISTRIBUTION AND CHARACTERIZATION OF Vibrio cholerae IN APALACHICOLA BAY, FLORIDA

Vibriosis in the U.S. is commonly associated with consumption of raw oysters harboring Vibrio vulnificus or V. parahaemolyticus.  V. cholerae O75, however, has been associated with sporadic cases and one cholera outbreak from Florida oysters in 2011.  This research examined abundance and prevalence of V. cholerae from 2012 to 2014 at various sites in Apalachicola Bay, the primary oyster harvest location in Florida. V. cholerae was found in 50% of seawater and 48% of oyster samples, which was significantly lower than prevalence of V. vulnificus (93%, 100%) or V. parahaemolyticus (76%, 100%). Furthermore, V. vulnificus and V. parahaemolyticus were found in fish gut and were widely distributed throughout the Bay, while V. cholerae was not associated with fish and was more likely to be isolated from near-shore (71%) as compared to mid-bay (29%) sites. Inverse correlations of V. cholerae levels in seawater and oysters were observed with both salinity and conductivity, while positive correlation with dissolved oxygen was seen in oysters. No relationship was observed with these parameters and the other Vibrio species.

Whole genome sequencing determined that all V. cholerae strains from Florida water and oyster samples lacked genes necessary for cholera toxin expression (ctxA, ctxB) or acquisition (tcpA).  However, 88% of isolates collected exhibited known virulence genes (toxR, rtxA, hlyA, opmU). Multi-locus sequence typing showed genetically diverse populations from seawater, while isolates from oysters were more closely related to each other, and more likely to cluster with the O75 outbreak strain and other related non-O1 or non-O139 serogroups.  Antibiotic resistance, including multi-drug resistance, was observed.  This research provides baseline data for V. cholerae in Florida oysters and oyster production areas, and demonstrates limited risk for future outbreaks, as strains lacked the toxigenic potential required for epidemics of cholera.  However, the mechanism whereby the original outbreak strain acquired this potential is unknown and warrants further study.