Occurrence of Virulence Genes Associated with Human Pathogenic Vibrios Isolated from Two Commercial Dusky Kob (Argyrosmus japonicus) Farms and Kareiga Estuary in the Eastern Cape Province, South Africa

Abstract

<i>Background</i>: Seafood-borne <i>Vibrio</i> infections, often linked to contaminated seafood and water, are of increasing global public health concern. The aim of this study was to evaluate the prevalence of human pathogenic vibrios and their associated virulence genes isolated from fish and water samples from 2 commercial dusky kob farms and Kareiga estuary, South Africa. <i>Methods</i>: A total of 200 samples including dusky kob fish (<i>n</i> = 120) and seawater (<i>n</i> = 80) were subjected to <i>Vibrio</i> screening on thiosulfate-citrate-bile salts-sucrose agar (TCBS). Presumptive isolates were confirmed and delineated to <i>V. cholerae</i>, <i>V. parahaemolyticus</i>, <i>V. vulnificus</i>, and <i>V. fluvialis</i> by PCR. Various pathogenic gene markers were screened: <i>V. parahaemolyticus</i> (<i>trh</i> and <i>tdh</i>), <i>V. vulnificus</i> (<i>vcgE</i> and <i>vcgC)</i> and <i>V. fluvialis (stn, vfh,</i><i>hupO</i>, <i>vfpA</i>). Restriction Fragment Length Polymorphism (RFLP) of the <i>vvh</i>A gene of <i>V. vulnificus</i> strains was performed to determine the associated biotypes. <i>Results</i>: Total <i>Vibrio</i> prevalence was 59.4% (606/1020) of which <i>V. fluvialis</i> was the most predominant 193 (31.85%), followed by <i>Vibrio vulnificus</i> 74 (12.21%) and <i>V. parahaemolyticus</i> 33 (5.45%). No <i>V. cholerae</i> strain was detected. One of the <i>V. parahaemolyticus</i> strains possessed the <i>trh</i> gene 7 (9.46%) while most (91.9%; 68/74) <i>V. vulnificus</i> isolates were of the E-type genotype. <i>V. fluvialis</i> virulence genes detected were <i>stn</i> (13.5%), <i>hupO</i> (10.4%) and <i>vfpA</i> (1.0%). 12.16% (9/74) of <i>V. vulnificus</i> strains exhibited a biotype 3 RFLP pattern. <i>Conclusions</i>: This is the first report of potentially pathogenic vibrios from healthy marine fish in the study area, and therefore a public health concern.