Molecular characterization of pbp genes in beta-lactamic resistant pneumococcal strains.

ALBARRACIN ORIO AG; CORTES PR; TREGNAGHI M; PIÑAS GE; ECHENIQUE J

Cataratas Iguazu

Congreso; XL Reunión Anual de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular; 2004

The target for β-lactamic (βL) antibiotics are enzymes involved in the cell-wall biosynthesis, known as PBPs (penicillin-binding proteins). The βL-resistant strains present altered PBPs that reduce their affinity to β-lactamics. The goal of this work was to characterize at molecular level the pbp gene mutations of clinical pneumococci circulating in Cordoba City. From twenty four βLresistant strains isolated at Public Children Hospitals, we selected ten with the higher βL resistance. To identify the pbp mutations that confer βL resistance, these genes were amplified and PCR products and transformed to an uncapsulated βL-susceptible strain. For transformants with pbp1a or pbp2b altered genes, a two-fold increase was obtained using as reference the wild-type penicillin MIC, whereas pbp2x altered genes produced changes ranging from one to three-fold increase. For cefotaxime, pbp2x or pbp2b altered genes produced two- to three-fold increase in its MIC value. We could not find individual altered pbp genes able to confer MIC values equal to those from the original strain. To characterize these altered pbp genes, genetic polymorphisms were investigated by RFLP analysis. Two types for pbp1a/pbp2b and four types for pbp2x were detected. All clinical strains were genotyped by PCR-BOX, and four different box patterns were identified. We found no close relationship between pbp and box types, indicating that the βLresistance spreading was caused by different strains, but harbouring a few pbp gene patterns that were transferred between them.