Sources and fate of Salmonella and fecal indicator bacteria in an urban creek

Abstract

This research aimed to understand the sources and fate of Salmonella and fecal bacteria in urban surface waters. An urban creek (San Pedro Creek, California, USA) that had unusually high levels of Salmonella and fecal bacteria relative to other nearby waterbodies was chosen as a model field site. State of the art microbiological methods were used in concert with modeling to investigate Salmonella and fecal bacteria sources, and determine field-relevant dark inactivation and photoinactivation rates. Three along-creek surveys that spanned reaches adjacent to both urban and forested land covers were conducted to measure Salmonella, enterococci, Escherichia coli, and horse- and human-specific Bacteroidales. Salmonella were detected adjacent to and downstream of urban land cover, but not adjacent to forested land cover. No human or horse-specific Bacteroidales fecal markers were detected implicating other urban animal sources of bacteria. Two locations along the creek where Salmonella was consistently detected were sampled hourly for 25 hours and a mass-balance model was applied to determine field-relevant light and dark inactivation rates for Salmonella, enterococci, and E. coli. Sunlight inactivation did not appear to be important in modulating concentrations of Salmonella, but was important in modulating both enterococci and E. coli concentrations. Dark inactivation was important for all three organisms. This is the first study to quantitatively examine the fate of Salmonella within an urban surface water. Although the work is carried out at a single site, the methodologies are extendable to source tracking in other waterbodies. Additionally, the rate constants determined through the modeling will be useful for modeling these organisms in other surface waters, and represent useful benchmarks for comparison to laboratory-derived inactivation rates.

Landscape, Water Quality, and Weather Factors Associated With an Increased Likelihood of Foodborne Pathogen Contamination of New York Streams Used to Source Water for Produce Production

“…Bradshaw et al (2016) also reported that the odds of stx detection increased by a factor of 2 for each log 10 increase in ruminant FST marker concentration, which is similar to the odds ratio calculated here (OR = 1.6; 95% CI = 1.1, 2.4). The identification of an association between hostassociated FST markers, and Salmonella and eaeA-stx codetection is also consistent with the associations between spatial factors and microbial target detection identified here and in past studies (Sassoubre et al, 2011;Walters et al, 2011;Wilkes et al, 2011;Bradshaw et al, 2016). For instance, Wilkes et al (2011) identified a positive association between pasture being present 0-5 km upstream of a sampling site, and an increased likelihood of isolating E. coli O157:H7 from water samples collected in Ontario, Canada.…”

Mechanisms for Photoinactivation of Enterococcus faecalis in Seawater

“…The concentrations of these bacteria, however, are known to be highly variable (6,7,59,60). Intensive field studies show that their concentrations fluctuate on diurnal timescales due to sunlight exposure; concentrations drop during sunlit hours and rise after the sun sets (8,21,50,60,61). While enterococcal photoinactivation is well documented, the mechanisms of inactivation are not well understood, limiting our ability to predict when the process will be important under the wide range of conditions that exist in natural and engineered systems.…”

Photoinactivation of Eight Health-Relevant Bacterial Species: Determining the Importance of the Exogenous Indirect Mechanism

“…bacterial inactivation in natural waters. The inactivation of Escherichia coli and to a lesser extent enterococci has been measured in a wide range of sunlit waters and the observed inactivation rate constants vary over several orders of magnitude 15,[21][22][23][24][25][26] . There are limited studies on sunlight inactivation of waterborne bacterial pathogens such as Campylobacter, Vibrio cholerae, Shigella,…”