Approches génétique et bioinformatique pour la prédiction de la structure 3D de la PLP2a du gène mecA de Staphylococcus aureus.

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is a major public health problem, causing both nosocomial and community-acquired infections worldwide. Methicillin resistance is generally due to the mecA gene which encodes an additional penicillin binding protein (PBP2a) with low affinity for methicillin and all beta-lactam antibiotics. The first part of our thesis, consists in identifying 65 isolates of S. aureus, collected from different pathological samples in Constantine, by MALDI-TOF MS. Our results showed a high reliability and rapid identification of S. aureus by proteomics technology MALDI-TOF MS compared to phenotypic and genotypic techniques (sequencing of the 16S rDNA). Resistance to methicillin in these strains was detected by the cefoxitin disk diffusion method in Mueller-Hinton agar, accompanied by the search for the mecA gene by RT-PCR. The comparison between these two methods revealed a high degree of correlation. The second part of our thesis, consists of the prediction of the secondary and tertiary structures of PBP2a in sillico by the use of appropriate bioinformatics tools. The knowledge of the 3D structure of PBP2a has allowed us to better understand its function as well as the resistance mechanism of MRSA to methicillin. Alignment of our tertiary structures of PLP2a of LISC8 and PMC1 isolates generated by MODELLER shows a mutation in positions 124 and 182 where asparagine ""N"" is substituted by lysine ""K"".