Abundance of clinical enteric bacterial pathogens in coastal waters and shellfish

Abstract

In order to study the prevalence of enteric pathogens capable of causing clinical illness in the environment, bacterial isolates collected from diarrhoeal patients, coastal waters and shellfish (including oysters, mussels and clams) were analysed by comparing their serotypes and by examining for the presence of particular pathogenic characteristics in the environmental isolates. Salmonellae (66%) dominated the 1211 bacterial isolates from diarrhoeal patients, followed by campylobacters (13%) and shigellae (6%). Vibrios and salmonellae made up the majority (85%) of the 458 isolates from coastal waters and shellfish. Among 870 Salmonella isolates serotyped, high incidences of S. typhimurium and S. enteriditis isolated from diarrhoeal patients were not observed in the case of the coastal waters nor shellfish. The Salmonella serotype distribution of clinical isolates, in general, were different from those isolated from coastal waters as well as shellfish. The most commonly isolated Salmonella species from the environmental samples were S. derby (13.7%) and S. infantis (12.3%) with serogroup O4 (31.5%) being the most commonly isolated serogroup. Among all the Vibrio ssp. isolated from the environmental samples, neither V. cholerae O1 causing epidemic infection worldwide nor V. cholerae O139 which had been reported to cause epidemics in India and Bangladesh in 1992 and 1993 was found. For the V. parahaemolyticus isolates, all clinical isolates produced thermostable direct haemolysin (Vp- TDH), while only a small percentage (1.5%) of the environmental isolates could produce Vp-TDH. In conclusion, no significant common characteristics had been found between the clinical isolates and those from the environmental sources.