Viable but nonculturable Vibrio cholerae O1 in biofilms in the aquatic environment and their role in cholera transmission

Munirul Alam, Marzia Sultana, G. Balakrish Nair, A. K. Siddique, Nur A. Hasan, R. Bradley Sack, David A. Sack, K. U. Ahmed, A. Sadique, H. Watanabe, Christopher J. Grim, A. Huq, Rita R. Colwell

Research output: Contribution to journalArticle

Abstract

Vibrio cholerae persists in aquatic environments predominantly in a nonculturable state. In this study coccoid, nonculturable V. cholerae O1 in biofilms maintained for 495 days in Mathbaria, Bangladesh, pond water became culturable upon animal passage. Culturability, biofilm formation, and the wbe, ctxA, and rstR2 genes were monitored by culture, direct fluorescent antibody (DFA), and multiplex PCR. DFA counts were not possible after formation of biofilm. Furthermore, wbe, but not ctxA, were amplifiable, even after incubation for 54 and 68 days at room temperature (≈25°C) and 4°C, respectively, when no growth was detectable. Slower biofilm formation and extended culturability were observed for cultures incubated at 4°C, compared with ≈25°C, suggesting biofilm production to be temperature dependent and linked to loss of culturability. Small colonies appearing after incubation in microcosms for 54 and 68 days at 25°C and 4°C, respectively, were wbe positive and ctxA and rstR2 negative, indicating loss of bacteriophage CTXΦ. The coccoid V. cholerae O1 observed as free cells in microcosms incubated for 495 days could not be cultured, but biofilms in the same microcosms yielded culturable cells. It is concluded that biofilms can act as a reservoir for V. cholerae O1 between epidemics because of its long-term viability in biofilms. In contrast to biofilms produced in Mathbaria pond water, V. cholerae O1 in biofilms present in cholera stools and incubated under identical conditions as the Mathbaria pond water biofilms could not be cultured after 2 months, indicating that those V. cholerae cells freshly discharged into the environment are significantly less robust than cells adapted to environmental conditions.

Original languageEnglish (US)
Pages (from-to)17801-17806
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume104
Issue number45
DOIs
StatePublished - Nov 6 2007

Keywords

  • Bacteriophage CTXΦ
  • Bangladesh
  • DFA
  • Multiplex-PCR
  • ctxA

ASJC Scopus subject areas

  • General

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    Alam, M., Sultana, M., Balakrish Nair, G., Siddique, A. K., Hasan, N. A., Bradley Sack, R., Sack, D. A., Ahmed, K. U., Sadique, A., Watanabe, H., Grim, C. J., Huq, A., & Colwell, R. R. (2007). Viable but nonculturable Vibrio cholerae O1 in biofilms in the aquatic environment and their role in cholera transmission. Proceedings of the National Academy of Sciences of the United States of America, 104(45), 17801-17806. https://doi.org/10.1073/pnas.0705599104