Loads and virulence of bacterial isolates associated with the finfish (<i>Caranx hullianus</i>) harvested from Okwanobolo River Estuary

Loads and virulence of bacterial isolates associated with finfish, Caranx hullianus, from the estuarine water of Okwanobolo River in Eastern Obolo, Niger Delta, Nigeria was investigated. The total heterotrophic bacterial count (THBC), total coliform count (TCC), faecal coliform count (FCC), Salmonella-Shigella count (SSC), and Vibrio count (VC) of flesh, gills, and intestines of the fish samples were determined using standard bacteriological methods. Virulence factors of the selected bacterial isolates were also determined using microbiological techniques. The THBC and TCC of the flesh recorded mean log count of 5.12 CFU/g and 4.11 CFU/g respectively while FCC, SSC, and VC were not detected. The intestines had the highest bacterial counts while the flesh had the least. The THBC, TCC, FCC and SSC of the gills recorded mean values of 5.48 log CFU/g, 4.31 log CFU/g, 1.67 log CFU/g, and 1.82 log CFU/g respectively with no VC detected. The THBC, TCC, FCC and SSC of the intestines recorded mean value of 5.61 log CFU/g, 4.42 log CFU/g, 4.31 log CFU/g, and 2.62 log CFU/g respectively with no VC detected. The analysis of variance revealed significant differences among the physiological groups in the flesh (p = 1.36E 32 <0.05); gills (p = 7.18E-06 <0.05) and intestine (p = 1.67E-10 <0.05). Of the eight bacterial species associated with the samples, Proteus sp. and Staphylococcus aureus were common in all the fish tissues. However, Escherichia coli, Streptococcus sp., Bacillus subtilis, Klebsiella sp., Salmonella sp. and Shigella sp. were isolated only from the fish gills and intestines. These isolates exhibited varying virulence potentials concerning DNase, Gelatinase, Lipase, Coagulase, and Urease markers. Staphylococcus aureus recorded the highest occurrence (100%) for all the virulence markers while Escherichia coli, Klebsiella sp. and Shigella sp. recorded the least occurrence (20%). Finfish from the estuarine environment habour potentially pathogenic microorganisms.