A tentative national reference procedure for isolation and enumeration of Escherichia coli from bivalve molluscan shellfish by most probable number method

Abstract

In the UK several quantitative methods exist for the examination of bivalve molluscan shellfish for sewage contamination. These methods include roll tubes, pour plates and most probable number (MPN) techniques, but there is no national standard method. A comparative study was made of the most commonly used methods for detection of Escherichia coli in bivalve shellfish. Schemes employing solid media, such as the roll tube and pour plate methods, underestimated faecal contamination in shellfish tissue compared with a liquid MPN multiple test-tube method using minerals-modified-glutamate broth (MMGB) as primary enrichment medium. The composition of MMGB apparently permits repair of sublethally injured cells of E. coli. Incorporation of resuscitation stages into the pour plate technique did not yield higher counts. A standardized MPN technique for examination of bivalve molluscan shellfish for E. coli content is proposed as a possible national reference procedure pending further collaborative assessment.

Development of a method for detection of enteroviruses in shellfish by PCR with poliovirus as a model

“…Environmentally contaminated oysters (Ostrea edulis) were obtained from The Solent (England), and mussels were obtained from the River Exe (England), both areas of which are affected by sewage discharges. Escherichia coli counts in shellfish were assayed by a multiple tube most probable number procedure incorporating a resuscitation stage in mineral-modified glutamate broth (42). Depurated shellfish contained less than 230 E. coli per 100 g of shellfish flesh and fluid.…”

Heavy‐metal and microbial depuration of the clam Ruditapes decussatus and its effect on bivalve behavior and physiology

“…Freshly harvested shellfish samples comprising 50 clams from each site were randomly subdivided into five subsamples of 10 clams each. The subsamples were scrubbed with a sterile knife, and microbial groups were enumerated using the plate count method as described by West and Coleman (1986). Homogenates of the 10 bivalves in 45 mL of peptone water (0.01% Tween-80) were serially diluted in phosphate buffer, and suitable dilutions were plated onto the appropriate agar medium.…”

“…Bivalves also accumulate microorganisms, including pathogenic bacteria and viruses, when grown in polluted waters and can present a significant health risk when consumed raw or lightly cooked (West and Coleman, 1986;Rippey, 1994;Sobsey and Jaykus, 1999;Croci et al, 2002;Formiga-Cruz, 2003). Pathogenic bacteria, such as Salmonella typhi, Vibrio parahaemolyticus and V. cholera remain viable for weeks in the marine environment, whereas viruses can survive for months in the same environment as well as in fish tissue.…”

Bacteriophage as models for virus removal from Pacific oysters (Crassostrea gigas) during re-laying

“…Water and sewage samples were examined for phages using the same plating techniques as for shellfish. Numbers of E. coli were estimated using the technique of West and Coleman [18].…”