EFFECTS OF ENVIRONMENTAL-FACTORS PRESENT IN THE ST-LAWRENCE ESTUARY (QUEBEC, CANADA) ON EXPERIMENTAL SURVIVAL OF SALMONELLA-SALAMAE AS DETERMINED BY FLOW-CYTOMETRY

Survival of Salmonella salamae in the St. Lawrence Estuary was studied experimentally during an oceanographic cruise using in situ exposure diffusion chambers. The abundance distribution (colony-forming units) of culturable S. salamae on media was compared with the distribution of cells enumerated by flow cytometry. Flow cytometry was also used to characterize the size distribution and DNA content of cells exposed to various environmental factors. Solar radiation, starvation, and a gradual increase in salinity led to an abrupt loss of the ability of S. salamae cells to form cultures and to a gradual reduction in the cell size and DNA content. Conversely, starvation combined with a gradual increase in salinity in the absence of sunlight led to st gradual loss of the cells' ability to form cultures and an abrupt reduction in cell size and DNA content (i.e., a rapid increase in cell damage). Mortality (i.e., a decrease in total cell count) of S. salamae placed in darkness began at a lower salinity (11.4 parts per thousand) than did the mortality of cells exposed to sunlight (23.1 parts per thousand). Therefore, the S. salamae cells exposed to sunlight seemed to be more resistant to gradual salinity stress than the cells that were not subjected to sunlight.