Compensatory Evolution of pbp Mutations Restores the Fitness Cost Imposed by ß-Lactam Resistance in Streptococcus pneumoniae
Andrea G. Albarracín Orio, Germán E. Piñas, Paulo R. Cortes, Melina B. Cian, José Echenique*
Departamento de Bioquímica Clínica - CIBICI (CONICET), Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina
Abstract
The prevalence of antibiotic resistance genes in pathogenic bacteria is a major challenge to treating many infectious diseases. The spread of these genes is driven by the strong selection imposed by the use of antibacterial drugs. However, in the absence of drug selection, antibiotic resistance genes impose a fitness cost, which can be ameliorated by compensatory mutations. In Streptococcus pneumoniae, ß-lactam resistance is caused by mutations in three penicillin-binding proteins, PBP1a, PBP2x, and PBP2b, all of which are implicated in cell wall synthesis and the cell division cycle. We found that the fitness cost and cell division defects conferred by pbp2b mutations (as determined by fitness competitive assays in vitro and in vivo and fluorescence microscopy) were fully compensated by the acquisition of pbp2x and pbp1a mutations, apparently by means of an increased stability and a consequent mislocalization of these protein mutants. Thus, these compensatory combinations of pbp mutant alleles resulted in an increase in the level and spectrum of ß-lactam resistance. This report describes a direct correlation between antibiotic resistance increase and fitness cost compensation, both caused by the same gene mutations acquired by horizontal transfer. The clinical origin of the pbp mutations suggests that this intergenic compensatory process is involved in the persistence of ß-lactam resistance among circulating strains. We propose that this compensatory mechanism is relevant for ß-lactam resistance evolution in Streptococcus pneumoniae.
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Citation: Albarracín Orio AG, Piñas GE, Cortes PR, Cian MB, Echenique J (2011) Compensatory Evolution of pbp Mutations Restores the Fitness Cost Imposed by ß-Lactam Resistance in Streptococcus pneumoniae. PLoS Pathog 7(2): e1002000. doi:10.1371/journal.ppat.1002000
Editor: Bruce Levin, Emory University, United States of America
Received: November 1, 2010; Accepted: December 10, 2010; Published: February 17, 2011
Copyright: © 2011 Albarracín Orio et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. |
