Diversity and Antimicrobial Resistance of Salmonella enterica Isolates from Surface Water in Southeastern United States

A study of prevalence, diversity, and antimicrobial resistance ofSalmonella enterica in surface water in the southeastern United States was conducted. A new scheme was developed for recovery ofSalmonella from irrigation pond water and compared with the FDA'sBacteriological Analytical Manual (8th ed., 2014) (BAM) method. Fifty-one isolates were recovered from 10 irrigation ponds in produce farms over a 2-year period; nineSalmonella serovars were identified by pulsed-field gel electrophoresis analysis, and the major serovar wasSalmonella enterica serovar Newport (S . Newport,n = 29), followed byS. enterica serovar Enteritidis (n = 6),S. enterica serovar Muenchen (n = 4),S. enterica serovar Javiana (n = 3),S. enterica serovar Thompson (n = 2), and other serovars. It is noteworthy that the PulseNet patterns of some of the isolates were identical to those of the strains that were associated with theS . Thompson outbreaks in 2010, 2012, and 2013,S . Enteritidis outbreaks in 2011 and 2013, and anS . Javiana outbreak in 2012. Antimicrobial susceptibility testing confirmed 16S . Newport isolates of the multidrug resistant-AmpC (MDR-AmpC) phenotype, which exhibited resistance to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, and tetracycline (ACSSuT), and to the 1st, 2nd, and 3rd generations of cephalosporins (cephalothin, amoxicillin-clavulanic acid, and ceftriaxone). Moreover, theS . Newport MDR-AmpC isolates had a PFGE pattern indistinguishable from the patterns of the isolates from clinical settings. These findings suggest that the irrigation water may be a potential source of contamination ofSalmonella in fresh produce. The newSalmonella isolation scheme significantly increased recovery efficiency from 21.2 (36/170) to 29.4% (50/170) (P = 0.0002) and streamlined the turnaround time from 5 to 9 days with the BAM method to 4 days and thus may facilitate microbiological analysis of environmental water.