Long distance travel of V.cholerae

Here, I will discuss the article (Munro and Colwell 1996) that had ‘demonstrated’ the long distance carriage of V. cholerae.

The objective of their study was

“The objective of this study was to determine the effect on survival in the marine environment of V. cholerae grown under high osmotic pressure prior to exposure to seawater, in order to test the hypothesis that such survival would allow transport of V. cholerae via ocean currents to distant geographical locations.”

The authors have incubated V. cholerae, pre-grown in different media, in seawater microcosms for 60 days. Bacterial counts were determined during the 60-day period. They found that cells previously grown in 0.5M sucrose showed a decrease of 2 log units after transfer to seawater microcosm for the first 10-12 days and maintained their number for the next 50 days. They also found that cells previously grown in M9 or M9Na showed a decrease of 3-5 log units for the first 10-12 days followed by an increase in the number of cells for the next 50 days to the same number of cells pre-grown in a medium containing sucrose.

Based on the results, the authors concluded that

“In conclusion, this study demonstrates that, under certain conditions, V. cholerae can remain in a culturable state in the marine environment for very long periods of time, months or even years. The significance of this finding is obvious in view of recent outbreaks of cholera in coastal cities of Latin America where transport by oceanic currents is hypothesized.”

Does this finding have any significance as claimed by the authors? The authors were testing the hypothesis that the survival of the organism would allow transport of V. cholerae via ocean currents. Where in this article have they tested this hypothesis? Similarly, where in the article have they demonstrated that the organism can be carried via ocean currents to distant geographic locations? Moreover, isn’t it true that, under certain laboratory conditions, bacteria (not only Vibrio) can remain viable for long periods?

Interestingly, this article has been cited in subsequent reviews as the evidence for the long distant carriage of the organism, thus misleading the readers.

Next- Was toxigenic V. cholerae present in the aquatic environment of Peru before the outbreak?

Munro, P. M. and Colwell, R. R. (1996). Fate of Vibrio cholerae O1 in seawater microcosms. Wat. Res. 30(1): 47-50