Microbial Quality of Tropical Inland Waters and Effects of Rainfall Events

Abstract

dNovel markers of fecal pollution in tropical waters are needed since conventional methods recommended for other geographical regions may not apply. To address this, the prevalence of thermotolerant coliforms, enterococci, coliphages, and enterophages was determined by culture methods across a watershed. Additionally, human-, chicken-, and cattle-specific PCR assays were used to identify potential fecal pollution sources in this watershed. An enterococcus quantitative PCR (qPCR) assay was tested and correlated with culture methods at three sites since water quality guidelines could incorporate this technique as a rapid detection method. Various rainfall events reported before sample collection at three sites were considered in the data analyses. Thermotolerant coliforms, enterococci, coliphages, and enterophages were detected across the watershed. Human-specific Bacteroides bacteria, unlike the cattle-and chicken-specific bacteria, were detected mostly at sites with the corresponding fecal impact. Enterococci were detected by qPCR as well, but positive correlations with the culture method were noted at two sites, suggesting that either technique could be used. However, no positive correlations were noted for an inland lake tested, suggesting that qPCR may not be suitable for all water bodies. Concentrations of thermotolerant coliforms and bacteriophages were consistently lower after rainfall events, pointing to a possible dilution effect. Rainfall positively correlated with enterococci detected by culturing and qPCR, but this was not the case for the inland lake. The toolbox of methods and correlations presented here could be potentially applied to assess the microbial quality of various water types.

Alternative Fecal Indicators and Their Empirical Relationships with Enteric Viruses, Salmonella enterica, and Pseudomonas aeruginosa in Surface Waters of a Tropical Urban Catchment

“…This suggests that the two techniques correlate well with each other in detecting E. coli and ENT in tropical surface waters, similar to previous studies (12,23). However, the qPCR results correlated better with pathogens.…”

“…From our correlation analysis, only E. coli and ENT showed a moderately strong negative relationship with the duration of the dry period. This is consistent with studies by Wilkes et al (29) but contrasts with others, which show that rainfall correlates well either with ENT but not E. coli (23) or with only E. coli (30). Singapore has a typical tropical climate, which favors the regrowth of E. coli and ENT in natural waters (31).…”

“…Rainfall can affect loading dynamics, either by dilution or indirectly by flushing microbes trapped in soils and sediments from previous contamination events (23). From our correlation analysis, only E. coli and ENT showed a moderately strong negative relationship with the duration of the dry period.…”

Predicting Salmonella Populations from Biological, Chemical, and Physical Indicators in Florida Surface Waters

“…A study in Puerto Rico attempted to correlate rainfall from 24 h, 48 h, and 1 week prior to water sampling for fecal coliforms and found no correlation between fecal coliforms and precipitation in any of the 10 sampling sites (40). Santiago-Rodriguez et al (40) suggested that rainfall may cause correlations to increase due to resuspension of fecal coliforms from sediments but that rainfall may have a possible dilution effect on fecal coliform concentrations, which may lower correlations (40).…”

“…Santiago-Rodriguez et al (40) suggested that rainfall may cause correlations to increase due to resuspension of fecal coliforms from sediments but that rainfall may have a possible dilution effect on fecal coliform concentrations, which may lower correlations (40). Some studies have indicated that turbulence caused by rainfall may resuspend pathogens or indicator microorganisms from sediments, raising their levels in the waters by 100-or 1,000-fold and that the depth and size of the water body dampen any rainfall dilution effect on the indicator/pathogen levels (7).…”