ABSTRACT
The membrane of methicillin-resistant Staphylococcus aureus (MRSA) contains penicillin-binding proteins (PBPs) in the phospholipidic bilayer, with the protein PBP2a being linked with the resistance mechanism. In this work we confirm the role of PBP2a with molecular-level information obtained with Langmuir monolayers as cell membrane models. The MRSA cell membrane was mimicked with a mixed monolayer of dipalmitoyl phosphatidyl glycerol (DPPG) and cardiolipin (CL), also incorporating PBP2a. The surface pressure-area isotherms and the Brewster angle microscopy (BAM) images for these mixed monolayers were significantly affected by the antibiotic meropenem, which is PBP2a inhibitor. The meropenem effects were associated with the presence of PBP2a, as they were absent in the Langmuir monolayers without PBP2a. The relevance of PBP2a was confirmed with results where the antibiotic methicillin, known to be unsuitable to kill MRSA, had the same effects on mixed DPPG/CL and DPPG/CL-PBP2a monolayers since it prevented PBP2a from incorporating in the monolayer. The biological implication of the findings presented here is that a successful antibiotic against MRSA should be able to interact with PBP2a, but in the membrane.
Subject(s)
Methicillin-Resistant Staphylococcus aureus , Anti-Bacterial Agents/metabolism , Anti-Bacterial Agents/pharmacology , Bacterial Proteins/metabolism , Meropenem/metabolism , Meropenem/pharmacology , Methicillin/pharmacology , Microbial Sensitivity Tests , Penicillin-Binding Proteins/metabolism , Penicillin-Binding Proteins/pharmacologyABSTRACT
Objetivo: Determinar si existe asociación entre genes implicados en la codificación de PBP2a con la expresión fenotípica de resistencia a meticilina en cepas de Staphylococcus spp. Diseño: Descriptivo Transversal. Metodologias: e determinó la resistencia y sensibilidad de 67 aislamientos, mediante pruebas fenotípicas (difusión en disco, concentración inhibitoriamínima CIM, producción de PBP2a y pruebas genotípicas para detectar los genes mecA y sus reguladores mecR1 y mecI por Reacción em Cadena de la Polimerasa (PCR). Resultados: De 9 cepas de S. aureus resistentes por difusión en disco solo 1 fue sensible por CIM. De 7 cepas resistentes por CIM, fueron sensibles por difusión en disco. Por el contrario las 7 cepas de Staphylococcus coagulasa negativo sensibles por difusión en disco fueron resistentespor CIM.En cuanto a la prueba de producción de PBP2a, los resultados fueron discordantes con la prueba de difusión en disco en 20..
Objective: Determining the association between genes involved in the codifi cation of Penicillin Binding Proteins 2A (PBP2A) with the phenotypic expression of methicillin resistance in Staphylococcus spp. Strains Design: Descriptive cross sectional Methodology: The sensitivity of 67 isolates was determined by means of a phenotypic test (disk diffusion, minimum inhibitory concentration CIM, production of PBP2a) and genotype tests to detect the mecA gene and its regulatory mecR1 and mecI by Polymerase Chain Reaction (PCR). Results: From 9 S. aureus resistant strains by disk diffusion 1 was sensitive by CIM, 7 CIM resistant strains were sensitive by disk diffusion. The 7 coagulase negative (CNS) sensitive strains by disk diffusion were resistant by CIM. By production of PBP2a, the results were discordant with the disk diffusion test in 20% and 34%with CIM. The genotype, reveals that, from 60 S.aureus strains 10(17%), and 7 S. coagulase negative strains 4 (57%) carry the mecA gene. From 10 S. aureus mecA positive strains, 5 carry the mecR1 gene and 7 carry the mecI gene. Of the 4 strains of S.coagulase negative mecA positive 2 carry the mecR1 and 2 carry the mecI gene. Conclusion: There is no association between genotype and phenotype in Staphylococcus spp. methicillin resistant strains, since, the resistance is due to many factors that the classical phenotypic test does not include.