Phytoplankton linked viable non-culturable Vibrio cholerae O1 (VNC) from rivers in Tucuman, Argentina

Abstract

Plankton-linked Vibrio cholerae has been detected in aquatic environments since the first decades of the 20th century. Several mechanisms have been proposed to explain the survival of V. cholerae during inter-epidemic periods, one of which is through existence in its viable non-culturable (VNC) form in biological reservoirs. This latent form of V. cholerae (VNC) would explain the seasonal outbreaks and the way the pathogen survives in the environment. The objectives of this study were to assay V. cholerae O1 in its viable non-culturable form in two rivers in Tucumán, Argentina, as well as its possible association to phytoplankton and its relation to four environmental variables (pH, temperature, conductivity and dissolved oxygen), using direct immunofluorescence. Analysis of phytoplankton revealed that diatoms were predominant with percentages between 85 and 100%. Nitzschia palea was the only species found at all three sample sites with percentages between 0 and 38%. Of the 54 samples obtained during the 18 sampling periods, V. cholerae VNC was detected through direct immunofluorescence in 39% of the cases and at all three sampling sites. Positive samples were analysed for association of VNC with phytoplankton and between 1 and 10 bacteria were found adhered to a single algal cell. This confirms for the first time in northwestern Argentina adherence of this microorganism to the genera Stigeoclonium and Nitzschia as environmental reservoirs. No correlation could be found between the latent form of Vibrio and the environmental variables assayed.