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.

[Listeriosis in Tunis: seven cases reports]. / Les infections à Listeria monocytogenes à Tunis: à propos de sept cas.

Listeria monocytogenesis a Gram positive facultative intracellular bacterium that can be responsible for severe infections, affecting essentially pregnant women, immunocompromised patients at the early and later stages of life. In Tunisia, invasive L. monocytogenes infections are thought to be exceptional and limited data are available about listeriosis. We reported seven cases (five newborn children and two infants) of human listeriosis that occurred in Tunis from 2000 to 2008. The newborn children were hospitalized for suspicion of maternofoetal infections. The two infants were hospitalized for fever associated with digestive signs in one case and neurological signs in the other. L. monocytogenes-was isolated from culture of cerebrospinal fluid in four cases, peripheral samples in two cases and from blood culture in one case. Isolates identification was based on conventional methods. Antimicrobial susceptibility was realized according to the recommendation of the "Comité de l'antibiogramme de la Société française de microbiologie". All L. monocytogenes isolates were sensitive to amoxicillin and aminoside but resistant to 3rd generation cephalosporins. Investigations of the immune system were realized for the two infants including phenotypic analysis of peripheral blood cells by flow cytometry, lymphocyte proliferation assays, phagocytic cell functions and measurement of immunoglobulins as well as complement. All these explorations were normal for both infants. The outcome was fatal in only one case (a newborn child), and all the other patients recovered after adapted antibiotic treatment. In conclusion, our study shows that listeriosis is not exceptional in Tunis. Thus, it is necessary to know how to evoke this diagnosis, at any age, in order to establish an early and adapted antibiotic treatment and to avoid fatal outcome.