Bivalve molluscs and human health

Clostridium difficile is an anaerobic, gram positive, spore forming bacillus, first identified in 1935 in healthy newborn infants’ faecal matter. Since then this C. difficile has been identified in many warm blooded animals as well as vegetables and shellfish. C. difficile was first found to produce two toxins, enterotoxin and cytotoxin, and has been associated with human illness through the years, producing symptoms such as diarrhoea and intestinal perforation, in extreme cases the toxins produced have lead to fatalities. If C. difficile were to occur within the tissues of edible marine fauna then this could pose a real threat to human health as human consumption of shellfish is quite high. This paper has chosen to research the occurrence of C. difficile in edible marine bivalve molluscs within the region of Naples. This choice will undoubtedly have been influenced by the ease at which they can acquire samples for study.

The authors of the paper sampled their edible bivalve molluscs from local fishmongers and food stalls, as well as the nearby purification centres and mussel farms. This way of sampling molluscs allows for a more thorough way of checking for the incidence of C. difficile within marketed populations of molluscs, as a sample taken from the wild would inevitably include a mixture of mature and juvenile molluscs, which may or may not contain levels of C. difficile which are representative of the molluscs which are commercially farmed and consumed. The authors found that 49% of the samples analysed were contaminated with C. difficile.

The paper theorises that the high rates of contamination found within their samples could be a result of the filter feeding of bivalve molluscs. As an assumption on how C. difficile entered the tissues of the bivalve molluscs sampled, it is the most plausible as the seawater around the bivalves is drawn within the shell of the organism and C. difficile present in the water column can be deposited and sequestered within the tissues of the bivalves. The question of how C. difficile made it into the water column surrounding the samples when originally C. difficile was identified in the faecal matter of newborn infants still remains. The authors briefly mentioned that sewage pollution can provide a source of harmful bacteria, though it was not specified that C. difficile was distributed through the water column it is heavily implied that this is the major possibility.

This paper outlines the need for further study into this particular topic in order to assess the full impact C. difficile incidence levels in commercially important bivalve molluscs will have upon human health worldwide. This is a prudent statement to make as this study only really gives enough evidence to draw preliminary conclusions.

Pasquale V., Romano V., Rupnik M., Capuano F., Bove D., Aliberti F., Krovacek K., Dumontet S., 2012, Occurrence of toxigenic Clostridium difficile in edible bivalve molluscs, Food Microbiology, 31, 309-312