Abstract
Coliphages are alternative fecal indicators that may be suitable surrogates for viral pathogens, but majority of standard detection methods utilize insufficient volumes for routine detection in environmental waters. We compared three somatic and F+ coliphage methods based on a paired measurement from 1 L samples collected from the Great Lakes (n = 74). Methods include: 1) dead-end hollow fiber ultrafilter with single agar layer (D-HFUF-SAL); 2) modified SAL (M-SAL); and 3) direct membrane filtration (DMF) technique. Overall, D-HFUF-SAL outperformed other methods as it yielded the lowest frequency of non-detects [(ND); 10.8%] and the highest average concentrations of recovered coliphage for positive samples (2.51 ± 1.02 [standard deviation, SD] log10 plaque forming unit/liter (PFU/L) and 0.79 ± 0.71 (SD) log10 PFU/L for somatic and F+, respectively). M-SAL yielded 29.7% ND and average concentrations of 2.26 ± 1.15 (SD) log10 PFU/L (somatic) and 0.59 ± 0.82 (SD) log10 PFU/L (F+). DMF performance was inferior to D-HFUF-SAL and M-SAL methods (ND of 65.6%; average somatic coliphage concentration 1.52 ± 1.32 [SD] log10 PFU/L, no F+ detected), indicating this procedure is unsuitable for 1 L surface water sample volumes. This study represents an important step toward the use of a coliphage method for recreational water quality criteria purposes.
Highlights
Coliphages are alternative fecal indicators that may be suitable surrogates for viral pathogens, but majority of standard detection methods utilize insufficient volumes for routine detection in environmental waters
We evaluate the performance of three somatic and F+ coliphage methods with 1 L sample volumes, including dead-end hollow fiber ultrafiltration (Mull and Hill, 2012; Smith and Hill, 2009) with single-agar layer (SAL) (D-HFUF-SAL) (McMinn et al, 2017), an improved direct membrane filtration procedure (DMF) (Sobsey et al, 2004) and SAL (United States Environmental Protection Agency, 2001b) modified to accommodate a 1 L sample volume (M-SAL)
The DMF method did not yield any F+ coliphage results from Lake Michigan samples, but they were detected using the other two methods (Fig. 1A) with D-HFUF-SAL (0.32 ± 0.34 [SD] log10 plaque forming unit (PFU)/L) method resulting in higher average concentration for positive samples as compared to the M-SAL (0.05 ± 0.26 [SD] log10 PFU/L) (Fig. 1A)
Summary
Coliphages are alternative fecal indicators that may be suitable surrogates for viral pathogens, but majority of standard detection methods utilize insufficient volumes for routine detection in environmental waters. We evaluate the performance of three somatic and F+ coliphage methods with 1 L sample volumes, including dead-end hollow fiber ultrafiltration (Mull and Hill, 2012; Smith and Hill, 2009) with SAL (D-HFUF-SAL) (McMinn et al, 2017), an improved direct membrane filtration procedure (DMF) (Sobsey et al, 2004) and SAL (United States Environmental Protection Agency, 2001b) modified to accommodate a 1 L sample volume (M-SAL).
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