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

Abstract

A study of prevalence, diversity, and antimicrobial resistance of Salmonella enterica in surface water in the southeastern United States was conducted. A new scheme was developed for recovery of Salmonella from irrigation pond water and compared with the FDA's Bacteriological Analytical Manual (8th ed., 2014) (BAM) method. Fifty-one isolates were recovered from 10 irrigation ponds in produce farms over a 2-year period; nine 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. 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 the S. Thompson outbreaks in 2010, 2012, and 2013, S. Enteritidis outbreaks in 2011 and 2013, and an S. Javiana outbreak in 2012. Antimicrobial susceptibility testing confirmed 16 S. 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, the S. 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 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 to 9 days with the BAM method to 4 days and thus may facilitate microbiological analysis of environmental water.

Distribution and Characterization of Salmonella enterica Isolates from Irrigation Ponds in the Southeastern United States

“…This study provides a systematic survey of 10 irrigation ponds located within an important agricultural region in southern Georgia and northern Florida (38,39) and represents the most comprehensive research (i.e., the largest number of samples and strains examined) to date on the risk of Salmonella contamination in agricultural water or pond sediments in the southeastern United States. The overall prevalence (38%) of Salmonella in surface water samples was similar to that in a prior report (39%) for the same ponds during an overlapping time period, using different methodologies (24). The present study also included quantitative analysis, which indicated that the Salmonella values for water samples were relatively low (overall geometric mean ϭ 0.3 MPN/liter) compared to the values found in investigations of river samples within this region, which showed 79 to 96% occurrence of Salmonella and levels from nondetectable up to 5,400 MPN/100 ml (8,9).…”

“…Another indication of human impact is the presence of MDR Salmonella strains in agricultural settings, as resistant isolates are generally thought to be derived from livestock exposed to a broad range of antibiotics (44). Relatively high numbers of antibioticresistant strains were isolated from these irrigation ponds (20% with resistance to 2 or more antibiotics), which was consistent with a smaller-scale investigation of Salmonella from the same ponds in 2011 to 2013 showing 33% MDR among 51 isolates tested (24). Interestingly, the most common profile of 10 antibiotics reported in the previous study was not observed in our survey.…”

“…The 10 ponds examined in this study (18,19,24) were located within the watersheds of the Upper Suwannee, Withlacoochee, and Ochlocknee Rivers located in the southern and southern coastal plains of Georgia and Florida (Fig. 1).…”

“…Several recent studies have focused on a group of ponds distributed throughout this area in southern Georgia. The levels of Escherichia coli O157 (18) and Campylobacter jejuni (19) were examined, and another independent study surveyed the prevalence, antibiotic resistance, and diversity of Salmonella in the same ponds (24). The objectives of this study were to quantify the spatial and temporal distribution, antibiotic resistance, and genetic diversity of Salmonella populations in both pond water and sediment samples in the context of the utility of fecal indicators and/or other environmental parameters for prediction of Salmonella.…”

Salmonella enterica Serovar Typhi and Paratyphi Responsible of Typhoid and Paratyphoid Fevers Transmitted by Environment and Food

“…The increase in food-borne outbreaks may be attributed to two factors: the improved surveillance of Salmonella contaminations of fresh produce over the years and the growing consumption of fresh produce due to a shift in people's eating habits toward healthier lifestyles where more vegetables and fruits instead of meat are consumed. It is predicted that consumption and production of fresh produce will continue to rise (Dubowitz et al, 2014;Li et al, 2014). Given that irrigation water can be a source of Salmonella contamination of vegetables, the prevention of outbreaks could be accomplished by consistent monitoring of the presence of Salmonella enterica in water supplies.…”