Purpose: The purpose of this study was evaluate the microbial quality of South Florida surface waters.
Methods: Water samples (1 liter) were collected monthly for twelve months at eight study sites along canals in South Florida. Samples were analyzed for turbidity, air temperature, water temperature, pH, and oxidation-reduction potential. Precipitation and relative humidity data were collected from the Florida Automated Weather Network. Samples were enumerated for total aerobic plate count, total coliforms and generic Escherichia coli. Samples were enumerated for Salmonella with a three-by-three MPN. Samples were inoculated in tetrathionate broth and Rappaport-Vassiliadis broth dilutions and incubated at 35 or 42°C for 24 or 48h, respectively, prior to streaking onto XLT-4 and Chromagar Salmonella. Presumptive Salmonella colonies were confirmed by invA PCR and serotyped.
Results: Salmonella was isolated from 26% of samples (25 of 96). Salmonella concentrations ranged from 0.50 to 3.00 log MPN/100 ml. Coliform populations ranged from 2.60 to 5.20 log MPN/100 ml. Aerobic plate counts were 3.80 to 6.10 log CFU/100 ml. Salmonella detection was not associated with E. coli or coliform populations or chemical or physical water characteristics. Geometric means of E. coli ranged from 0.88 to 1.82 log MPN E. coli/100 ml and statistical threshold values ranged from 1.59 to 2.47 log MPN E. coli/100 ml.
Significance: Salmonella populations are present in South Florida surface waters and cannot be predicted by total coliforms, generic E. coli or chemical and physical water characteristics. These data suggest these South Florida surface water sources will meet Produce Safety Rule water quality criteria; additional work is needed to evaluate at least 20 samples per source and use methods required by the PSR.