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Occurrence of somatic and F+ coliphage in Gulf of Mexico recreational waters
Citation:
Kelleher, J., A. Pemberton, B. McMinn, AND A. Korajkic. Occurrence of somatic and F+ coliphage in Gulf of Mexico recreational waters. ASM Microbe 2023, Houston, TX, June 15 - 19, 2023.
Impact/Purpose:
Somatic and F+ coliphage have been proposed as viral indicators of fecal pollution in recreational water settings. However, additional information is needed regarding their concentrations in marine waters and relationship with bacterial indicators of fecal pollution such as enterococci.
Description:
Recreational quality of marine waters is routinely assessed by enumeration of fecal indicator bacteria (FIB), such as enterococci. However, fate and transport of FIB and enteric viruses, a leading cause of recreational waterborne disease outbreaks, differs suggesting that viral indicators may be better suited for recreational water quality applications. Somatic and F+ coliphage have been proposed as viral indicators as a better predictor of viral pathogen presence in recreational waters, but paired measurements of enterococci and coliphages are needed to better inform future recreational water quality criteria development.Paired measurements of enterococci, somatic and F+ coliphage were generated from 169 water samples collected from three Gulf of Mexico beaches, including: Sylvan Beach, TX (SB; n=57), East Courthouse Beach, MS (EC; n=52) and Picnic Island, FL (PI; n=60). Enterococci (colony forming units: CFU) were enumerated using standard membrane filtration technique followed by incubation on mEI agar. Coliphages (plaque forming units: PFU) were enumerated using dead-end hollowfiber ultrafiltration and single agar layer assay which allowed for simultaneous quantification of both coliphage groups from two-liter water samples. Enterococci were detected in all samples, in concentrations ranging from 0.18 to 3.28 log10 CFU/100 mL which were significantly higher than coliphages (p < 0.0001). Somatic coliphages were detected in 96% of samples at levels (0.30-3.22 log10 PFU/L) significantly (p < 0.0001) higher than F+ coliphage (0.30 – 2.13 log10 PFU/L), which were detected sporadically (in 24% of samples). A recommended single sample maximum enterococci criteria (110 CFU/100 mL) was exceeded in 32% of samples and more frequently at EC (42%) and PI (40%) sites than SB (14%). While highest coliphage concentrations (≥ 100 PFU/L) were typically observed at EC (n=16 for somatic and n=1 for F+ coliphage), they didn’t necessarily coincide with enterococci exceedances.We consistently observed higher enterococci concentrations at all sites, compared to coliphages, which is in agreement with general distribution of these indicators in human fecal pollution sources. However, the difference between enterococci exceedances and highest coliphage concentrations may indicate additional fecal sources and suggests different fate and transport characteristics. Future research is needed to determine whether bacterial or viral indicators are better predictors of viral pathogen presence in marine waters.
