Comparison of Salmonella enterica serovar distribution and antibiotic resistance patterns in wastewater at municipal water treatment plants in two California cities.

AIM To determine Salmonella enterica serovars and antibiotic resistance (ABR) in the human waste stream. METHODS AND RESULTS Sampling of influent wastewater at municipal treatment plants in two California cities was performed by collecting composite samples, over a 24-h period, from the treatment plants on five to six occasions. Serial water quantities were filtered and cultured with a Salmonella selective method and an oxytetracycline-supplemented Salmonella selective method. Antibiotic susceptibilities to 12 antibiotics were determined and the isolates were grouped based on ABR patterns. From 983 S. enterica isolated, 102 represented unique sampling-serovar-ABR patterns. Thirty-five different serovars were identified to be distributed over 17 different ABR patterns. The serovar distribution differed between the sampling sites, whereas there was no significant trend in levels of multiple ABR. CONCLUSIONS Salmonella enterica was recovered with ease from small sample volumes of wastewater received by municipal water treatment plants. A large variety of serovars and ABR profiles were represented in the recovered Salmonella. SIGNIFICANCE AND IMPACT OF THE STUDY The ease of sampling and recovery of Salmonella from municipal wastewater from treatment plants makes it a valuable sampling approach for monitoring the presence of Salmonella in the human population.