Isolation of viable but nonculturable Vibrio cholerae O1 from environmental water samples in Kolkata, India, in a culturable state

Previously, we reported that viable but nonculturable (VBNC) Vibrio cholerae was converted into a culturable state by coculture with several eukaryotic cell lines including HT-29 cells. In this study, we found that a factor converting VBNC V. cholerae into a culturable state (FCVC) existed in cell extracts of eukaryotic cells. FCVC was nondialyzable, proteinase K-sensitive, and stable to heating at <60°C for 5 min. We prepared thiosulfate citrate bile salts sucrose (TCBS) plates with FCVC (F-TCBS plates). After confirming that VBNC V. cholerae O1 and O139 formed typical yellow colonies on F-TCBS plates, we tried to isolate cholera toxin gene-positive VBNC V. cholerae from environmental water samples collected in urban slum areas of Kolkata, India and succeeded in isolating V. cholerae O1 El Tor variant strains harboring a gene for the cholera toxin. The possible importance of VBNC V. cholerae O1 as a source of cholera outbreaks is discussed.