B05005: Development of procedures to distinguish between human and animal faecal contamination in shellfisheries
Tuesday 11 May 2004
This research project aims to develop methods to distinguish between animal and human wastes contaminating molluscan shellfish.
Study Duration: August 1999 to December 2002
Contractor: Centre for Environment, Fisheries and Aquaculture Science (CEFAS)
Background
During the process of filter feeding, bivalve molluscan shellfish such as oysters and mussels, can accumulate human pathogens originating from sewage polluted waters. The major pathogens that cause outbreaks of sickness and diarrhoea in the community are viruses, particularly Norovirus (NV). It is not possible to detect these viruses in shellfish without the use of technologically complex molecular methods, which are time consuming, difficult and expensive. Therefore faecal coliforms and E. coli have been adopted as indicator organisms to assess the quality of shellfish flesh and to predict the risk of exposure to pathogenic viruses. However, E. coli and faecal coliforms are found in both human and animal wastes. Existing methods for counting these bacteria do not distinguish between bacteria of human and animal origin. To help assess the potential risk to the consumer, and to assist in alleviating the problem of organic contamination of shellfisheries, it is important to know if the pollutant is of human sewage or agricultural origin.
Research Approach
Microbiological and chemical methods of typing faecal contamination of shellfish tissue will be developed and applied during this research. The methods include speciation of FRNA bacteriophages, detection of bacteriophages of Bacteroides fragilis, detection of human adenoviruses, detection of HH1 (human specific) marker in E. coli , gas chromatography mass spectrometry detection of sterols and gas chromatography mass spectrometry detection of caffeine.
A series of method validation and evaluation analyses will be completed against panels of human influents/effluents and animal wastes. Commercially produced oysters and mussels originating from shellfish growing waters representative of all classification categories as defined in European Directive 91/492/EEC will be tested using the procedure. Selected methods that show promise, will then be applied to shellfish from two shellfish harvesting areas in a field survey.
Results and findings
This study has shown that microbiological source tracking methods are potentially powerful tools that could be used to define the nature of shellfish quality problems and thus be beneficial to both the shellfish industry and its consumers. Some of these methods show potential but are still in the early stages of development.
The findings demonstrated that speciation of FRNA bacteriophage and detection of adenovirus can potentially be used in the analysis of shellfish tissue and provide additional information about conventional indicator organisms. Additionally, the enumeration of FRNA bacteriophage is well standardised, amenable to accreditation and thus could easily be adopted in routine laboratories. The PCR based presence-absence testing for adenoviruses is limited not only by the molecular methodology and ambiguous specificity but also by uncertainties over excretion rates and the potential number of uncharacterised veterinary adenoviruses.
Further research is required to define the current state of knowledge regarding source-tracking techniques, particularly with their application to shellfish tissue. A comprehensive review is required to form a basis for designing studies to compare, evaluate and validate a range of methods, taking into consideration measurements, reliability, relevance and cost.
Dissemination information
Final report is available from the FSA Library and Information centre. To obtain a copy, please contact the Enquiry Desk, Dr Elsie Widdowson Library and Information Services, Food Standards Agency (Tel: +44 (0) 20 7276 8181/8182 or by e-mail to: library&info@foodstandards.gsi.gov.uk).