Distribution and Characterization of Salmonella enterica Isolates from Irrigation Ponds in the Southeastern United States.
Irrigation water has been implicated as a likely source of produce contamination by Salmonella enterica. Therefore, the distribution of S. enterica was surveyed monthly in irrigation ponds (n = 10) located within a prime agricultural region in southern Georgia and northern Florida. All ponds and 28.2% of all samples (n = 635) were positive for Salmonella, with an overall geometric mean concentration (0.26 most probable number [MPN]/liter) that was relatively low compared to prior reports for rivers in this region. Salmonella peaks were seasonal; the levels correlated with increased temperature and rainfall (P < 0.05). The numbers and occurrence were significantly higher in water (0.32 MPN/liter and 37% of samples) than in sediment (0.22 MPN/liter and 17% of samples) but did not vary with depth. Representative isolates (n = 185) from different ponds, sample types, and seasons were examined for resistance to 15 different antibiotics; most strains were resistant to streptomycin (98.9%), while 20% were multidrug resistant (MDR) for 2 to 6 antibiotics. DiversiLab repetitive extragenic palindromic-element sequence-based PCR (rep-PCR) revealed genetic diversity and showed 43 genotypes among 191 isolates, as defined by >95% similarity. The genotypes did not partition by pond, season, or sample type. Genetic similarity to known serotypes indicated Hadar, Montevideo, and Newport as the most prevalent. All ponds achieved the current safety standards for generic Escherichia coli in agricultural water, and regression modeling showed that the E. coli level was a significant predictor for the probability of Salmonella occurrence. However, persistent populations of Salmonella were widely distributed in irrigation ponds, and the associated risks for produce contamination and subsequent human exposure are unknown, supporting continued surveillance of this pathogen in agricultural settings.
Department of Food Science and Human Nutrition, University of Florida, Gainesville, Florida, USA.
Zhiyao
Z
Luo
Emerging Pathogens Institute and Department of Plant Pathology, University of Florida, Gainesville, Florida, USA.
Ganyu
G
Gu
Department of Food Science and Human Nutrition, University of Florida, Gainesville, Florida, USA.
Amber
A
Ginn
Department of Statistics, University of Florida, Gainesville, Florida, USA.
Mihai C
MC
Giurcanu
Biological and Agricultural Engineering Department, University of Georgia, Tifton, Georgia, USA.
Paige
P
Adams
Biological and Agricultural Engineering Department, University of Georgia, Tifton, Georgia, USA.
George
G
Vellidis
Emerging Pathogens Institute and Department of Plant Pathology, University of Florida, Gainesville, Florida, USA.
Ariena H C
AH
van Bruggen
Department of Food Science and Human Nutrition, University of Florida, Gainesville, Florida, USA Citrus Research and Education Center, University of Florida, Lake Alfred, Florida, USA.
Michelle D
MD
Danyluk
Food Science and Nutrition Department and The Emerging Pathogens Institute, University of Florida, Gainesville, Florida, USA acw@ufl.edu.
Anita C
AC
Wright
D057914:Agricultural Irrigation; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D058491:Bacterial Load; D024881:Drug Resistance, Bacterial; D005431:Florida; D014644:Genetic Variation; D005838:Genotype; D005845:Georgia; D008826:Microbial Sensitivity Tests; D058889:Molecular Typing; D061005:Ponds / Q000382:microbiology*; D019779:Salmonella enterica / Q000145:classification / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification*; D012621:Seasons
D000900:Anti-Bacterial Agents