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 o f 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 gra dual increase in salinity led to an abrupt loss of the ability of S. s alamae cells to form cultures and to a gradual reduction in the cell s ize and DNA content. Conversely, starvation combined with a gradual in crease in salinity in the absence of sunlight led to st gradual loss o f the cells' ability to form cultures and an abrupt reduction in cell size and DNA content (i.e., a rapid increase in cell damage). Mortalit y (i.e., a decrease in total cell count) of S. salamae placed in darkn ess began at a lower salinity (11.4 parts per thousand) than did the m ortality of cells exposed to sunlight (23.1 parts per thousand). There fore, the S. salamae cells exposed to sunlight seemed to be more resis tant to gradual salinity stress than the cells that were not subjected to sunlight.