Copepods and Vibrio cholerae: A New Probe for Detection of Attached Bacteria Using Fluorescence in situ Hybridization

Objectives/Research Questions: Planktonic copepods, which exist in symbiotic relationships with Vibrio cholerae bacteria, have been implicated in the spread of cholera. Study goals include improved V. cholerae detection and investigation of symbiont spatiotemporal distribution. Microscopic detection of symbiotic V. cholerae has not been achieved in environmental samples. Fluorescent in situ hybridization (FISH) is a technique that offers specific molecular detection and microscopic visualization of cells in situ, but difficulties in distinguishing V. cholerae and closely related Vibrio mimicus have hindered its use.

Methods: A new, 16S rRNA-targeted oligonucleotide probe was developed that specifically tags V. cholerae while excluding V. mimicus.

Results: Results of FISH experiments using pure cultures show that the new probe produces a positive signal for V. cholerae O1 and non-O1 serotypes, but not V. mimicus. Conclusions: As demonstrated in this study, V. cholerae can be detected on whole copepod specimens using the new probe. In future studies to elucidate the involvement of copepods in cholera epidemics, this probe will be used to examine copepods and bacterial isolates obtained from the Artibonite River in Haiti, the purported environmental source of the current cholera epidemic in that country. Implications for Public Health The FISH probe designed in this study will serve as a valuable tool for visualization and detection of V. cholerae bacteria from environmental reservoirs.

Student Role in the Project: With intellectual support from the academic advisor, all research work and experiments were designed and conducted by the student.