Copepods and Cholera

A review of: Rawlings, Tonya K., Ruiz, Gregory M., Colwell, Rita R. 2007. Association of Vibrio cholerae O1 El Tor and O139 Bengal with the Copepods Acartia tonsa and Eurytemora affinis. Appl. Environ. Microbiol. 2007 73: 7926-7933

Uncoupling abiotic and biotic factors which influence the amplification and transmission of Vibrio cholerae is difficult. Two serotypes, V.cholerae 01 El Tor and 0139 Bengal have been identified as causative agents of cholera epidemics. Differences in yearly appearance recorded from past outbreaks suggest variability of resource usage efficiency between serotypes and responses to changing environment conditions in the aquatic habitat.

Aquatic organisms, particularly phytoplankton and zooplankton, are known to provide important microhabitats for V. cholerae. This study focused on two copeopod species, predominant in areas associated with cholera epidemics; Acartia tonsa and Eurytemora affinis . When incubated in microcosm treatments both copeopod species were colonised by the two serotypes of V. Cholerae, but to different extents. 01 El Tor colonised both copeopod species at higher abundances than 0139 Bengal. The authors suggestion of differences in colonization by these two serotypes across a variety of taxa is supported by Chiavelli et al (2001).

A methodical experimental approach is demonstrated by the authors. Relevant control treatments are included and sample independence problems arising from pseudo-replication in similar experimental designs have been considered. However the affects of differing abiotic factors are not addressed. Temperature and salinity in this design were carefully controlled constants despite these variables being important regulators of fluctuations of abundance of V. cholerae. The effects of these abiotic factors are briefly discussed by the authors. Knowledge of the interactions between these environmental conditions and plankton dynamics it is suggested would reveal more about abundance and distribution of V.cholerae however no further attempts were made in this study to address the effects of abiotic variables..

Despite this paper having clear aims and concise conclusions the inherent complexity of multi-treatment experiments leads to potentially impregnable methods and results sections. The level of detail presented does however reflect the readership targeted by the publishing journal. Applied Environmental Microbiology is #1 cited journal in microbiology, biotechnology and applied microbiology. Knowledge of bacterial processes and microbial methods could be assumed of the readership. Prior understanding would allow considerable in-roads to be made into appreciating the analytical techniques and experimental design utilised in this study and to fully integrate the large number of individual results being presented.

Overall, despite an intricate experimental design and initial daunting complexity of results the discussion and conclusions concisely summarise the studies findings and place them in clear context. Further work is required to reveal the interactions of the biotic and abiotic factors involved. This study nonetheless presents an valid step forwards in understanding the abundance, distribution and strategies utilised by V. cholerae which is important in understanding the characters of cholera outbreaks and epidemics in human populations.

Reference: Chiavelli, D. A., J. W. Marsh, and R. K. Taylor. 2001. The mannose-sensitive hemagglutinin of Vibrio cholerae promotes adherence to zooplankton. Appl.Environ. Microbiol. 67:3220–3225.

Posted by Ross Bullimore, February 2011