For nearly a century after the discovery in the 1880s that a bacterium, Vibrio cholerae, causes cholera, scientists believed that it traveled to new geographic regions only via human hosts and that epidemics typically occurred when the bacteria spread through contamination, by human waste, of food and unchlorinated water supplies. But scientists spontaneously around the world, often where it was thought to have been eradicated?
In the 1970s, microbiologist Rita Colwell’s claim that she had isolated V. cholerae from the Chesapeake Bay in the eastern United States met with great skepticism, as no biologists believed V. cholerae could persist without a human host, and no cholera outbreaks were occurring anywhere near the Chesapeake. Indeed, there had been 52 suspect water samples, whereas culture techniques found them in only 7 of the same samples.
Colwell’s further studies revealed that V. cholerae, like some other bacteria, goes into a dormant, sporelike state when environmental conditions do not favor reproduction; in this state, the bacterium’s metabolic rate plummets and the bacterium shrinks some 15-to 300-fold. It stops reproducing and therefore cannot be cultured. This “viable but nonculturable” state, that changes in seawater temperature or salinity are what enable them to spread among humans again.
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