A minimum infectious dose under control

Thanks to the support of Wallonia, Georges Daube worked in collaboration with Alain Vanderplasschen, Professor of immunology and vaccinology at ULg, and with Professor José Remacle of the University of Namur, in order to develop technologies to improve these methods. "The University of Namur has concentrated on the screening of pathogens in order to identify which ones are present in a given sample by the DNA microarrays  method", explains Georges Daube. "For our part we concentrated on another method of molecular biology, real-time PCR , which makes it possible to amplify specific  genes of microorganisms in order to detect pathogens and estimate their quantity". This quantitative aspect is crucial because, for each pathogen, there is a minimal infectious dose. Below this dose there is no health risk to humans because the pathogens will be destroyed in the stomach or the digestive system. "The method we have perfected and which has been the subject of an article in Food Control makes it possible therefore, not only to detect pathogens but to quantify them", explains the researcher.

Once the pathogens have been detected by the DNA microarrays or real-time PCR method, it is necessary to isolate the pathogens in order to be able to characterize them and to determine their virulence factors. "With Professor Vanderplasschen, we have developed antibodies coupled with magnetic particles which could be used to capture the microorganisms and enable us to specifically isolate them", continues Georges Daube.

An efficient method for seafood

Carried out between 2006 and 2008, this work led to the creation of an efficient method for the detection of six bacteria in seafood products: Campylobacter jejuni, Campylobacter coli, enterohaemorrhagic Escherichia coli O157, Salmonella spp, Vibrio parahaemolyticus, and Vibrio vulnificus.  "Commercial kits based on the PCR method have been on the market since 2008. These are used mainly for the qualitative method because the quantitative method requires the use of a reproducible method of DNA extraction. This stage is not always carried out in an optimal fashion and can therefore result in a false estimate of the quantity of pathogens present in a sample", explains the scientist.  despite the availability of commercial kits on the market, the recent publication of Professor Georges Daube's team confirms that the real-time PCR method can be considered as an optimal method in food quality control. "The advantage of our method is that it has been validated more specifically for the detection of pathogens on the matrices of live bivalve molluscs and on raw and cooked shrimps. Even though current marketing methods are standard for all foodstuffs, it is necessary to ensure that they perform well in terms of the matrix being studied. Otherwise there are risks of false negatives which can have very serious consequences", points out the researcher.

Rare but serious complications

The checks strongly limit the risk of contamination of consumers by seafood through the pathogens that these foods carry. However, it can happen that some pathogens escape the vigilance of authorities, producers or consumers themselves. What consequences can these pathogens have for human health?  "These are mainly bacteria and viruses that cattle, humans and poultry excrete in their feces which ends up in the sea", explains Georges Daube. "In most cases, these are bacteria which adhere to the cells that form the wall of the intestine thus causing diarrhoea, vomiting and fever. The most dangerous pathogens enter the cells of the intestine and destroy them which causes blood loss in stools. In rare cases, they can also enter the blood system and cause septicaemia, that is to say, a general infection of the organism. The immune system is them overcome and this can sometimes lead to death".