Thesis presented December 15, 2016

Abstract:
The presence of pathogenic micro-organisms in foodstuff is a major concern for health safety. Regulations impose, in most cases, the research of low levels of these bacteria. Although reference methods are simple, they are time-consuming and can require several days before obtaining results. This is why one of the major challenges in food hygiene science is the development of sensitive and rapid methods, for the detection of one or more pathogens. These new technologies aim to decrease the occurrence of foodborne infections, while improving both the shelf life of food products and industrial production costs (long storage times, recalls …). In this context, the development of an alternative method has been carried out in this work, using a biosensor with a transduction based on surface plasmon resonance (SPR). Such optical technology offers multiple benefits: ease-of-use, real-time analysis, label-free process… Proofs of concept for the use of this technology in basic conditions, for the detection of model bacteria, have been described in the literature, mostly using antibodies as receptors, but the full operation in "real" conditions encountered in industrial facilities still has to be tested and optimized. This manuscript thus describes the detection of foodborne pathogenic bacteria playing a major role in terms of prevalence and/or severity of the caused infection, whether Gram positive or negative. The production of efficient antibodies was optimized, resulting in polyclonal antibodies sensitive and specific for multiple bacterial genera. Dynamics of bacterial growths were analyzed by SPR in an effort to identify the main factors having an impact on the detection. High resolution SPR was used for a better understanding of reactions occurring at the surface of the biosensor. These studies lead to the development of a system capable of multiplex detection of low bacterial inoculum in food samples (lettuce and powdered infant formula) within less than 24 hours.

Keywords:
Pathogenic bacteria, SPRi, Multiplex detection, Biosensor, Antibody, Food industry