Scientific Publications by FDA Staff

Appl Environ Microbiol 2014 Oct 15;80(20):6355-65

Diversity and antimicrobial resistance of Salmonella enterica isolates from surface water in Southeastern United States.

Li B, Vellidis G, Liu H, Jay-Russell M, Zhao S, Hu Z, Wright A, Elkins CA

A study of prevalence, diversity, and antimicrobial resistance of Salmonella enterica in surface water in southeastern U.S. was conducted. A new scheme was developed for recovery of Salmonella from irrigation pond water, and compared with the FDA Bacteriological Analytical Manual method. Fifty-one isolates were recovered from ten irrigation ponds in produce farms over a two year period; 9 Salmonella serovars were identified by pulsed-field gel electrophoresis analysis, and the major serovar was Salmonella enterica serovar Newport (S. Newport, n=29), followed by S. Enteritidis (n=6), S. Muenchen (n=4), S. Javiana (n=3), S. Thompson (n=2), and other serovars. It is noteworthy that some of the isolates' PulseNet patterns were identical to those of the strains that were associated with the S. Thompson outbreaks in 2010, 2012, and 2013, S. Enteritidis outbreaks in 2011 and 2013, and a S. Javiana outbreak in 2012. Antimicrobial susceptibility testing confirmed 16 S. Newport isolates of 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 ceftriaxon). Moreover, the S. Newport MDR-AmpC isolates showed an indistinguishable PFGE pattern with that of the isolates from clinical settings. These findings suggest that the irrigation water may be a potential source of contamination of Salmonella in fresh produce. The new Salmonella 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 5-9 days to 4 days compared with the BAM method, and thus may facilitate the microbiological analysis on environmental water.