Understanding the effects of the environment on Vibrio cholerae: competition between pathogenic strains.
Butzler, Julia*,1, Cottingham, Kathryn1, 1 Dartmouth College, Hanover, NH, USA
ABSTRACT- The intestinal disease cholera is caused by the colonization of the human intestine by certain strains of the heterotrophic bacterium, Vibrio cholerae. There are both genotypic and phenotypic differences between strains, and epidemiological evidence suggests that different environmental conditions may favor different strains. The outcome of competition between strains could therefore influence which strains cause both endemic and pandemic cholera events. The classical biotype of the O1 serogroup dominated as the causative agent of pandemics until 1961, the seventh pandemic, when the O1 El Tor biotype was identified. El Tor has since displaced the classical biotype throughout much of the world. We hypothesize that the shift in dominant strains is due to the differing competitive abilities of O1 classical and O1 El Tor. Based on theory developed by Tilman (1982), we predicted the outcome of competition between El Tor and classical biotypes by considering the resource use of each strain for carbon, nitrogen and phosphorus. We further tested the competitive abilities under adverse environmental conditions. We found that there were, in fact, differential competitive abilities between biotypes. El Tor competitively excluded classical biotype under several nutrient scenarios. We also found additional environmental factors (e.g., disturbance) could influence the outcome of competition. These results increase our understanding of how environmental conditions can affect the global extent of cholera.
Key words: cholera, El Tor, classical, resources
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