Purpose: The effects of salinity on the in vitro growth and survival of pathogenic Vibrios were investigated.
Methods: Individual and co-inoculated cultures were assessed by plate count and multiplex QPCR (DuPont BAX) for growth in nutrient media at various salinities (5, 10, 20, 30, 35 ppt) and for survival in artificial seawater (ASW) following salinity upshifts (20 to 30 ppt or 20 to 35 ppt) at different temperatures (23 and 30 °C).
Results: The salinity range for optimum growth yield at 6 h differed for Vp (10 to 35 ppt); Vc (5 to10 ppt); and Vv (10 ppt). Higher yield of Vp in competitive culture at 35 ppt (P = 0.03) was the only observed difference for competitive vs. individual growth. Salinity upshifts did not alter survival of Vp after 32 days in ASW; whereas, Vv and Vc showed ca. 2.0 log CFU/ml reduction (P < 0.04) by plate count following upshifts from 20 to 30 ppt (but not 20 to 35 ppt) at 23°C (but not 30°C). However, reductions were not confirmed by QPCR, suggesting upshifts may induce a viable but nonculturable state. The only difference in competitive vs. individual survival in ASW was a greater reduction (P = 0.03) of Vv in the competitive sample following an upshift from 20 to 30 ppt at 23°C.
Significance: These quantitative data on the effects of salinity and temperature on growth and survival of Vibrio species suggest that design parameters for oyster relay practices should be carefully evaluated in order to optimize conditions for the reduction of Vibrio contamination of oysters.