E. coli Is a Poor End-Product Criterion for Assessing the General Microbial Risk Posed From Consuming Norovirus Contaminated Shellfish

Jasmine H Sharp,James E Mcdonald,Mallory Diggens,Davey L Jones,Shelagh K Malham,Katie Clements

doi:10.3389/fmicb.2021.608888

Jasmine H Sharp, James E Mcdonald + Show 4 more

Open Access

https://doi.org/10.3389/fmicb.2021.608888

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Abstract

The fecal indicator organism (FIO) Escherichia coli is frequently used as a general indicator of sewage contamination and for evaluating the success of shellfish cleaning (depuration) processes. To evaluate the robustness of this approach, the accumulation, retention, and depuration of non-pathogenic E. coli, pathogenic E. coli O157:H7 and norovirus GII (NoV GII) RNA were evaluated using a combination of culture-based (E. coli) and molecular methods (E. coli, NoV GII) after exposure of mussels (Mytilus edulis) to water contaminated with human feces. We simulated water contamination after a point-source release from a combined sewer overflow (CSO) where untreated wastewater is released directly into the coastal zone. All three microbiological indicators accumulated rapidly in the mussels, reaching close to maximum concentration within 3 h of exposure, demonstrating that short CSO discharges pose an immediate threat to shellfish harvesting areas. Depuration (72 h) in clean water proved partially successful at removing both pathogenic and non-pathogenic E. coli from shellfish tissue, but failed to eradicate NoV GII RNA. We conclude that current EU standards for evaluating microbiological risk in shellfish are inadequate for protecting consumers against exposure to human norovirus GII found in polluted marine waters.

Highlights

18 million tons of marine molluscs are harvested each year with an estimated value of $35 billion, comprising 9% of the value of fisheries worldwide (Wijsman et al, 2019; FAO, 2020)
Non-pathogenic E. coli accumulated in shellfish tissue from an initial mean concentration of 166 CFU to 1 × 105 CFU 100 g−1 within 3 h of exposure to water containing 5 × 106 CFU E. coli 100 ml−1 seawater (P = 0.030; Figure 1A)
We have shown under both controlled laboratory and field conditions in UK waters (Winterbourn et al, 2016) that the use of nonpathogenic E. coli as an end-product bacteriological criterion cannot reliably assess the general microbiological risk posed from consuming contaminated shellfish

Summary

Introduction

18 million tons of marine molluscs are harvested each year with an estimated value of $35 billion, comprising 9% of the value of fisheries worldwide (Wijsman et al, 2019; FAO, 2020). Microbiological contamination of molluscan shellfish can readily occur in areas where coastal waters are polluted with sewage effluent, and agricultural. Norovirus Risk From Consuming Mussels run-off, such that shellfish accumulate large amounts of bacterial or viral pathogens (Bosch et al, 1995; Burkhardt and Calci, 2000; Winterbourn et al, 2016). In many parts of the world, shellfish are grown in areas exposed to treated or untreated wastewater which may contain human pathogens (e.g., Cryptosporidium, hepatitis A/E, norovirus; Razafimahefa et al, 2020). Raw and undercooked shellfish can act as vectors of infectious pathogens which can pose a serious risk to human health (Flannery et al, 2014; Santos-Ferreira et al, 2020)

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