Evaluation of Direct Plating and Enrichment Methods for Isolation of Vibrio cholerae O139 from Faecal Samples

Abstract

In this study, direct-plate culture method alone, or in combination with enrichment culture for isolation of Vibrio cholerae O139 from faecal samples at a Diarrhoea Treatment Centre in Dhaka, Bangladesh had been evaluated. Faecal samples of 528 patients with acute phase of diarrhoea, attended the Centre, were cultured directly onto thiosulfate-citrate-bile-salts-sucrose agar (direct-TCBSA) and tellurite-taurocholate-gelatin agar (direct-TTGA) and after 6-h and overnight enrichment in alkaline-bile-peptone-broth for V. cholerae O139 (ABPB) [6h-ABPB-TCBSA and 6h-ABPB-TTGA, and overnight-ABPB-TCBSA and overnight-ABPBTTGA]. Direct-TTGA-plating and overnight-ABPB-TTGA methods (latter for samples yielding negative results by overnight-direct-TTGA cultures) were also performed for another 18,647 faecal samples submitted for culture in our laboratory and 1,552 rectal swabs transported in Cary-Blair medium during investigation of acute diarrhoea outbreaks in the country. During acute phase of diarrhoea, direct-TCBSA, or direct-TTGA cultures equally supported O139 growth, while direct-plating plus 6-h, or overnight enrichment cultures were not superior as compared to the direct-plating. Direct-TTGA-plating plus overnight-ABPB-TTGA increased O139 isolation from transported rectal swabs. Thus, direct-plating provides optimum stool culture results for V. cholerae O139 during acute phase of diarrhoea. However, a combination of direct-TTGA-plating and overnight- ABPB-TTGA cultures was useful for isolation of V. cholerae O139 from transported rectal swab samples.