Purpose: This study evaluated surface (nontidal freshwater (NF), tidal freshwater (TF), pondwater (PW), tidal brackish (TB)) water sources from eight sites in Maryland for the presence of Salmonella spp., Listeria monocytogenes (Lm), and Escherichia coli (Ec).
Methods: SNIW from eight sites (four NF, one TB, one TF, and two PW) were collected by traditional methods or filtered through modified Moore swabs. Sampling occurred on six different dates (September to December, 2016). Filters were quantified for E. coli populations (n=52) through standard methods (EPA 1604); Moore swabs were quantified for Salmonella spp. (n=32); and Lm populations (n=36) through a modified MPN procedure using 10-liter, 1-liter, and 0.1-liter volumes. Chemical parameters of water were measured. Culture-positive results for Salmonella spp. and Lm were confirmed through real-time PCR. One-way ANOVA on recovered pathogen populations in JMP were performed.
Results: Mean Salmonella spp. populations were 0.15+0.30, 0.11+0.10, 0.02+0.14, and 0.007+0.012 MPN/100 ml from NF, TF, TB, and PW sources, respectively. Mean Lm populations were 0.20+0.08, 0.28+0.17, 0.004+0.15, and 0.003+0.10 MPN/100 ml, respectively. Mean Salmonella spp. populations were significantly (P<0.05) higher at one NF site (MD05) compared to other sites. Lm populations at one NF site (MD08) were, also, significantly higher compared to other sites. From all water samples, 65% and 46% were positive for Salmonella spp. and Lm, respectively, and 53% contained Ec populations >126 CFU/100 ml. There were no significant correlations observed between Ec and either Lm or Salmonella spp. populations.
Significance: These data indicated that Salmonella spp. and Lm were present in multiple SNIW sources in Maryland. Year-round sampling is required to truly assess prevalence in this region.