Towards development of reliable biological method to detect and quantify AI-2 signals from Campylobacter jejuni in food samples

Abstract S3

Presenter: Dina Rami (Biotechnical faculty, University of Ljubljana)

For many years, there was a belief that bacteria were unicellular organisms, striving primarily to find nutrients and multiply. It is now known that bacteria communicate and coordinate their behaviour, which enables them to form highly organized multicellular entity. Moreover, bacteria can communicate within or between species using the quorum sensing mechanism (QS), which is controlled by AI-2 signalling molecules. Campylobacter jejuni is the most common bacterial foodborne pathogen causing mainly self-limiting gastrointestinal illness in humans worldwide. Although it is very sensitive to various environmental stressors, it is still one of the most problematic bacteria in the food industry. Campylobacter jejuni possesses the LuxS/AI-2 communication system, which enables these bacteria to express many adaptive properties such as stress response, chemotaxis, biofilm formation, virulence and pathogenicity. It is very important to study the QS mechanism of these bacteria so that we can modulate the properties of Campylobacter and mitigate the risks it presents for food safety. Our aim was to develop a reliable method to detect and quantify AI-2 signals from C. jejuni in food samples. First, we optimized a biological method and selected the most appropriate Vibrio harveyi reporter strain to study QS in C. jejuni. Furthermore, we quantified AI-2 signals in the spent medium of C. jejuni cultured in the Mueller-Hinton (MH) broth with biological method and selected V. harveyi reporter strain. For this purpose, we used the standard molecule DPD and fitted a Hill model to our data obtained from the response of V. harveyi. To confirm our results, we used an analytical method, HPLC-FLD for detection and quantification of AI-2 signals in the spent medium of C. jejuni. Finally, we aimed to detect and quantify AI-2 signals in the spent medium of C. jejuni cultured in the food model (5% chicken juice in MH broth) using the optimized biological method. We showed that V. harveyi MM30 (LuxS- mutant) responded the best to the spent medium of C. jejuni, so we used this strain in further experiments. The results obtained with V. harveyi MM30 and HPLC-FLD showed that C. jejuni produces M concentrations of AI-2 signals in the exponential growth phase. The same was observed in the spent medium of C. jejuni cultured in the food model (5% chicken juice in MH broth). M-concentrations of AI-2 signals were confirmed. In conclusion, the use of this biological method represents a reliable and affordable method that can be used to detect and quantify signalling molecules in a food sample.

Presenting in Speaking session 4 - Survival and application