Prevalence, identification by a DNA microarray-based assay of human and food isolates Listeria spp. from Tunisia.

OBJECTIVES: We aimed at evaluating the prevalence of Listeria species isolated from food samples and characterizing food and human cases isolates. MATERIAL AND METHODS: Between 2005 and 2007, one hundred food samples collected in the markets of Tunis were analysed in our study. Five strains of Listeria monocytogenes responsible for human listeriosis isolated in hospital of Tunis were included. Multiplex PCR serogrouping and pulsed field gel electrophoresis (PFGE) applying the enzyme AscI and ApaI were used for the characterization of isolates of L. monocytogenes. We have developed a rapid microarray-based assay to a reliable discrimination of species within the Listeria genus. RESULTS: The prevalence of Listeria spp. in food samples was estimated at 14% by using classical biochemical identification. Two samples were assigned to L. monocytogenes and 12 to L. innocua. DNA microarray allowed unambiguous identification of Listeria species. Our results obtained by microarray-based assay were in accordance with the biochemical identification. The two food L. monocytogenes isolates were assigned to the PCR serogroup IIa (serovar 1/2a). Whereas human L. monocytogenes isolates were of PCR serogroup IVb, (serovars 4b). These isolates present a high similarity in PFGE. Food L. monocytogenes isolates were classified into two different pulsotypes. These pulsotypes were different from that of the five strains responsible for the human cases. CONCLUSION: We confirmed the presence of Listeria spp. in variety of food samples in Tunis. Increased food and clinical surveillance must be taken into consideration in Tunisia to identify putative infections sources.

[Hepatitis A virus detection in shellfish from Tunisia by reverse transcription-nested PCR--investigation of a correlation between viral and bacterial contamination]. / Détection du virus de l'hépatite A dans les coquillages en Tunisie par reverse transcription-nested PCR - recherche de corrélation entre la contamination virale et bactérienne.

OBJECTIVES: We aimed at evaluating the contamination by hepatitis A virus (HAV) of 54 shellfish samples collected from five Tunisian shellfish harvesting areas and finding a correlation between bacterial and viral contamination. MATERIAL AND METHODS: Fifty-four shellfish samples were analysed in our study. Two methods of viral extraction were evaluated by reverse transcription-nested PCR. The first one was based on elution by glycine solution and the second one used a beef extract solution. Bacteriological determination (Samonella and E. coli) was carried out for all shellfish samples. RESULTS: Glycine extraction showed a higher detection rate of HAV compared to the saline beef extraction method. The hepatitis A virus was detected in 32 % of shellfish samples analysed. None of the samples revealed the presence of Samonella. From 17 samples positive for HAV, we found six samples showing a number of E. coli below the European legislation. CONCLUSION: An important HAV contamination was observed in our study. No correlation between bacterial and viral contamination was found.