Use of selective media to recover Salmonella and Vibrio cholerae after growth in reconditioned pork-processing wastewater

Abstract

Selective plating media are used for the enumeration and isolation of bacterial pathogens from food and water samples. This study compared the quantitative recovery of Salmonella spp. and Vibrio cholerae grown in nutrient-limited, filter-sterilized, reconditioned wastewater over the temperature range of 4 to 45°C using nonselective and pathogen-specific selective media. Viable Salmonella were enumerated on tryptic soy agar (TSA) and XLT-4, and viable V. cholerae were enumerated on TSA and thiosulfate-citrate-bile-sucrose agar. There was a statistically significant (P < 0.05) higher recovery of both pathogens over the growth temperature range on TSA compared to the selective media. Trehalose, a stress-induced metabolite of Salmonella, was isolated from the cells grown in the reconditioned wastewater, whereas, the V. cholerae exhibited a change in cellular morphology from rod to coccoid shape. These results suggest that growth in nutrient-limited water injured or stressed the individual pathogens. Care should be used in choosing the procedure and plating medium for quantitative recovery of pathogens from such a nutrient-limiting environment.