Ecology of Vibrio cholerae in Florida Bays

Introduction: Vibrio cholerae (Vc), the etiological agent of cholera, has been responsible for seven pandemics since 1817. U.S. outbreaks are rare, and only 8 sporadic cases were reported to CDC between 2003 and 2007. Recent epidemics in Haiti and Cuba confirmed cases due to the 7^th pandemic strain of Asiatic Vc. A Florida outbreak in 2011 was associated with raw oyster consumption and indicated emergence of a serotype (O75) that differed from pandemic Vc.

Purpose: This study investigated the genetic structure of Vc populations in Florida relative to toxigenic 7th pandemic Vc.

Methods: Water, sediment, oyster, fish and various plant samples were collected seasonally from 2011 to 2012 at different sites in Tampa and Apalachicola Bays. Environmental parameters, including temperature, salinity, pH, and dissolved oxygen were recorded. Presumptive Vc was isolated from CHROMagar™ and TCBS, and confirmed by rRNA intergenic spacer region-based PCR. Confirmed isolates were compared to clinical Vc by multilocus sequence typing (MLST) of five housekeeping genes (recA, gyrB, pyrH, gapA, and topA) and screened for cholera toxin gene, ctxA, by PCR.

Results: Vc was isolated from only water samples in Apalachicola and from both water and oysters in Tampa Bay. Unlike other Vibrio species, Vc was not widely distributed throughout the bay, but was mostly associated with near-shore sites with lower salinity. Most strains from Apalachicola (92%) and Tampa (63%) closely associated with a genetic clade that included Vc O75 and classical Vc 395 but were distinct from the 7^th pandemic Vc clade that included only one isolate from Apalachicola. Other strains formed unique clades. No environmental strain was positive for ctxA.

Significance: Vc is endemic to Florida waters but is divergent from the current 7^th pandemic strain, and virulence potential appears limited due to the absence of genes for cholera toxin.