Predicting how human disease causing Vibrio species will react to climate change.

  

Turner et al. (2014) investigated how seasonal changes in temperature and plankton abundance affect the prevalence of Vibrio parahaemolyticus, V. vulnificus and V. cholerae and subpopulations that harbour clinically associated genes. These Vibrio species are Gram-negative bacilli autochthonous to marine, estuarine and freshwater environments and a few environmental strains are capable of causing illness in humans most commonly indirectly through eating shellfish. Understanding the specific interactions between Vibrio subpopulations and seasonally predictable changes in biotic and abiotic factors can offer critical information needed to better understand changes in risk from environmental exposure.

For a period of one year, surface water and plankton samples (63-200μm and >200 μm) and environmental variables (surface water temperature and salinity) were collected bi-monthly from 12 commercial or public oyster harvesting sites along the South Atlantic Bight of coastal Georgia, USA. DNA samples were taken from water samples and concentrated plankton samples. PCR primers were then used to detect bacteria and clinically associated genes (Table 1). PCR was used to investigate the detection frequency of species-specific gene targets (i.e. present in all strains of a species), instead of culture-based methods. The benefits of using this technique instead include increased sensitivity (i.e. reduced false negatives) and reduced analysis times, which may outweigh risks of false-positive detection. 

V. parahaemolyticus, V. vulnificus and V. cholerae were frequently detected in bulk water and plankton net tow samples. Among all samples (n=210) V. parahaemolyticus was detected significantly more than V. vulnificus, which was detected significantly more than V. cholerae. V. vulnificus and V. cholera targets were only detected when water temperature exceeded >15 °C, however V. parahaemolyticus targets were detected in all water samples even when they dropped below 10 °C. Salinity had little effect on detection of Vibrio, only the ORF8 region of  V. parahaemolyticus was correlated with an increase in salinity. All Vibrio species increased in detection when there were more of an abundance of of chitinous zooplankton (copepods and decapods) and that of chitin- producing diatoms.

The results of this study suggest that some Vibrio species may exhibit a stronger chitin affinity compared with the general Vibrio community and may indicate some competitive advantage for a commensal lifestyle. Combined increases in temperature and shifts in plankton abundance may facilitate an expanded seasonal and geographic range of Vibrio species. In light of climate change predictions, which include increases in sea surface temperature as well as shifts in the range and composition of marine plankton communities, these results may inform future estimates of exposure risk and serve a baseline for future investigations. It would have been useful for the authors to explain the known distributions of the Vibrio  and zoo/phyto-plankton species that were found in this study, as this could then predict which routes and regions these species will colonise and cause problems in. 

Referance: Turner, J. W., Malayil, L., Guadagnoli, D., Cole, D., & Lipp, E. K. (2014). Detection of Vibrio parahaemolyticus, Vibrio vulnificus and Vibrio cholerae with respect to seasonal fluctuations in temperature and plankton abundance.Environmental microbiology, 16(4), 1019-1028.

Can be found at: http://onlinelibrary.wiley.com/doi/10.1111/1462-2920.12246/full