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Comparison of somatic and F+ coliphage enumeration methods with large volume surface water samples.

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.

SUBMITTER: McMinn BR

PROVIDER: S-EPMC7082814 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The increased association of enterohemorrhagic Escherichia coli (EHEC) with veal calves has led the United States Department of Agriculture Food Safety and Inspection Service to report results of veal meat contaminated with the Top 7 serogroups separately from beef cattle. However, detection methods that can also provide concentration for determining the prevalence and abundance of EHEC associated with veal are lacking. Here we compared the ability of qPCR and a molecular based most probable number assay (MPN) to detect and enumerate EHEC from veal hides at the abattoir and the resulting pre-intervention carcasses. In addition, digital PCR (dPCR) was used to analyze select samples. The qPCR assay was able to enumerate total EHEC in 32% of the hide samples with a range of approximately 34 to 91,412 CFUs/100 cm(2) (95% CI 4-113,460 CFUs/100 cm(2)). Using the MPN assay, total EHEC was enumerable in 48% of the hide samples and ranged from approximately 1 to greater than 17,022 CFUs/100 cm(2) (95% CI 0.4-72,000 CFUs/100 cm(2)). The carcass samples had lower amounts of EHEC with a range of approximately 4-275 CFUs/100 cm(2) (95% CI 3-953 CFUs/100 cm(2)) from 17% of samples with an enumerable amount of EHEC by qPCR. For the MPN assay, the carcass samples ranged from 0.1 to 1 CFUs/100 cm(2) (95% CI 0.02-4 CFUs/100 cm(2)) from 29% of the samples. The correlation coefficient between the qPCR and MPN enumeration methods indicated a moderate relation (R (2) = 0.39) for the hide samples while the carcass samples had no relation (R (2) = 0.002), which was likely due to most samples having an amount of total EHEC below the reliable limit of quantification for qPCR. Interestingly, after enrichment, 81% of the hide samples and 94% of the carcass samples had a detectable amount of total EHEC by qPCR. From our analysis, the MPN assay provided a higher percentage of enumerable hide and carcass samples, however determining an appropriate dilution range and the limited throughput offer additional challenges.

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Comparison of somatic and F+ coliphage enumeration methods with large volume surface water samples.

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