P-011. Serotype Identification of Listeria monocytogenes Colombian Isolates by Multiplex PCR

M. C. Vanegas, A. J. Martinez;
Univ. de los Andes, Bogota, COLOMBIA.

Background: Listeria monocytogenes is an important food borne microorganism due to its high mortality rate 30%. A serotyping method based on variation in the somatic (O) and flagellar (H) antigens have divided this microorganism in at least 14 different serotypes. The1/2a, 1/2b, and 4b serotypes represent more than 95% of the human listeriosis cases. This procedure is not performed routinely in Colombian laboratories and recent reports have stated conventional serotyping may lead to occasional misclassification. In this study we amplified virulence-specific genes related to the mayor serotypes of L.monocytogenes of Colombian isolates and compare it with its conventional serotype. Methods: A multiplex PCR was used in order to determine the molecular serotype of 56 L.monocytogenes strains from RTE products and food processing plants. Conventional serotyping was done by a reference laboratory in Colombia. Results: Molecular serotyping results revealed a 4b/4d serotype for 45 isolates, one isolate amplified for the 1/2a serotype and two isolates amplified for the 1/2c serotype. Only two isolates classified as 4b by conventional serotype correlated with the molecular serotyping results and 25 isolates classified as 4a by conventional serotype give a 4b/4d molecular serotype instead. Conclusions: These results show that virulence specific serotype genes can be used for detection and differentiation of principal L. monocytogenes serotypes since forty five isolates analyzed in this study yielded a specific serotype. This procedure is not performed routinely in microbiological food laboratories in our country therefore this technique will provide our country relevant results since a deep sub-registry situation on L. monocytogenes exists.