Purpose: The aim of this study was to understand the environmental distribution and diversity of Salmonella in North Florida surface waters and the association of environmental factors with Salmonella presence.
Methods: Surface water samples (10 l) were collected monthly for 12 months (11/2011-10/2012) from six sites located near agricultural lands in North Florida. Samples were analysed for physical and chemical characteristics; enumerated for total aerobic plate count (TPC), total coliforms, generic Escherichia coli and Salmonella by standard FDA-BAM methods. Salmonella isolates were characterized by serotyping, PFGE, and antimicrobial resistance. A previously published model for the probability of enumerating Salmonella as a function of E. coli concentration in Central Florida surface waters was evaluated for its applicability to this data.
Results: Salmonella was isolated from 21% (15/72) of water samples; 20 representative isolates (one isolate per site, per month, per serotype) were recovered. Serotypes included Salmonella Inverness, Muenchen, Saintpaul, IV_40:z4, z24:-, Florida, Hartford, and Anatum. One isolate was untypeable. Positive samples were evenly distributed across the sample sites. No positive samples were detected in the spring (March-May). Environmental factors (TPC, coliforms, E. coli, temperature, pH, ORP, turbidity) did not predict Salmonella presence/absence. Results collected here could not validate the previously published predictive model due to the low prevalence of Salmonella detected; the reported trend where increasing concentrations of E. coli correlated with increasing probabilities of detecting a Salmonella-positive sample was also observed. Proposed FSMA preharvest fruit-contact surface water standards require <235 MPN generic E. coli/100 ml in a single sample; 20% (14/72) of water samples (from 5/6 sources) were above this limit.
Significance: Salmonella populations are present in North Florida surface waters and cannot be predicted by the environmental factors evaluated or a previously published model.