Report No SR 97(03)F

Investigation of the relationship between indicator bacteria in mussel flesh and intervalvular fluid and surrounding waters Phase 1

SR 97(03)F

Dec 1997

EXECUTIVE SUMARY

  1. The EC Directive on the Quality of Waters for Shellfish Growth (79/923/EEC) stipulates a microbiological requirement of 300 faecal coliforms per l00ml of shellfish flesh and intervalvular fluid. After two years of sampling, it emerged, from results collated from all over the UK, that mussels collected from sites remote from any notable sewage input were consistently exceeding this standard. Archives revealed that there was a great dearth of research in this area; therefore it was decided, in 1992, to fund a preliminary investigation (report SR3553) into the relationship between FC levels in mussel FIV and their surrounding waters. It soon became clear that there was no empirical relationship, and, consequently this study was funded to explore the possibility of the existence of a complex relationship.
  2. The objectives of this study, which follows on from the work in SR3553, were i) to increase the time scale of the experiments, ii) to introduce a competing nutrient into the artificial sea water to observe if it would alter the FC balance, iii) to alter the salinity of the artificial sea water to observe if it would alter the FC balance, iv) to establish if other bacteria ( ie Faecal streptococci, Campylobacter and Clostridium perfringens) had an empirical relationship between mussel FIV and their surrounding water and, v) to establish an alternative to the MPN method that would be less expensive, more rapid and more reproducible.
  3. Mussels maintained in a continuous flow of potable water for 10 days, showed no statistically significant changes in FC FIV levels.
  4. Mussels maintained in pasteurised natural sea water showed a significant reduction in FC FIV levels after 7 days.
  5. Mussels maintained in pasteurised artificial sea water showed no significant reduction in FC FIV levels after 10 days
  6. Mussels maintained in pasteurised artificial sea water, with x100 the average estuary organic nutrients concentration retained a higher concentration of FC in the FIV, than the mussels maintained in pasteurised artificial sea water, with the average and x10 the average estuary organic nutrients concentrations. Similar results were obtained when Campylobacter FIV levels were examined.
  7. Mussels maintained in pasteurised artificial sea water with salinities of 100/00 and 540/00 retained higher FC FIV levels after 3 days than those maintained in salinities of 200/00, 270/00 and 400/00. Similar results were obtained when Campylobacter FIV levels were examined.
  8. The above results (3-7) indicate that the relationship between FC concentrations in mussels and the overlying waters is indeed complex and would probably take years to develop; therefore it was decided to look for an alternative indicator bacterium, which would display an empirical relationship.
  9. Mussels maintained in pasteurised artificial sea water showed a significant reduction in FS FIV levels after 8 days.
  10. There appeared to be a possible empirical relationship between mussel FIV FS concentrations and their adjacent water FS concentrations.
  11. There is a case developing in which FS could emerge as a useful indicator (9-10); therefore this work should be further developed in future studies.
  12. The most probable number (MPN) method was employed to enumerate the FS levels in the mussels; though proved time consuming, expensive and has poor confidence limits. Therefore, it was decided to attempt to develop a shorter, less expensive and more reproducible method. The FS pour plate method, which is currently under development, has returned very promising results, and, should be included in further studies.
  13. There appeared to be "no" empirical relationship between mussel FIV Clostridium perfringens concentration and their adjacent water Clostridium perfringens concentrations; therefore this work should not be developed in future studies.

KEY WORDS

Mussels, Mytilus edulis, artificial sea water, Faecal coliforms, Faecal streptococci, Campylobacter, Clostridium perfringens, salinity, organic nutrients, adjacent waters, depuration.

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