Growth and recovery of selected gram-negative bacteria in reconditioned wastewater

Previous reports indicate that Escherichia coli O157:H7, Salmonella spp., a nd Vibrio cholerae can grow in nutrient-limited, reconditioned wastewater o ver the temperature range of 4 to 46 degreesC when the biological oxygen de mand of this water is <2, while its coliform growth response (CGR) is >2. I n the current study, we investigated the growth response of Vibrio parahaem olyticus, Shigella spp., Vibrio vulnificus, and Pseudomonas aeruginosa in w ater samples with a CGR of >2 over the temperature range of 4 to 50 degrees C. Both the nonselective media, tryptic soy agar, and the selective media u sed to identify the pathogen were used for their recovery. The selective me dia were thiosulfate-citrate-bile-sucrose (TCBS), MacConkey agar (MAC), and Pseudomonas isolation agar (PIA) for the Vibrio, Shigella, and Pseudomonas spp., respectively. V. parahaemolyticus numbers declined rapidly after sur viving for 6 days under the nutrient-limiting growth conditions. Shigella s pp. did not grow but survived for > 28 days at 4 to 25 degreesC. V. vulnifi cus grew over the narrow temperature range of 12 to 21 degreesC and survive d for > 21 days at the higher and lower temperature ranges. P. aeruginosa s urvived and grew during the 14-day test period at 13 to 35 degreesC. Recove ry on the nonselective agar gave statistically (P > 0.05) higher numbers th an the respective selective media commonly used for these pathogens. These results indicate that caution should be used in attempting direct recoverie s using selective media of the four gram-negative bacteria species used in this study from the nutrient-limited water environment.