Biological cost and compensatory evolution in fusidic acid-resistant Staphylococcus aureus.
ABSTRACT Fusidic acid resistance resulting from mutations in elongation factor G (EF-G) of Staphylococcus aureus is associated with fitness costs during growth in vivo and in vitro. In both environments, these costs can be partly or fully compensated by the acquisition of secondary intragenic mutations. Among clinical isolates of S. aureus, fusidic acid-resistant strains have been identified that carry multiple mutations in EF-G at positions similar to those shown experimentally to cause resistance and fitness compensation. This observation suggests that fitness-compensatory mutations may be an important aspect of the evolution of antibiotic resistance in the clinical environment, and may contribute to a stabilization of the resistant bacteria present in a bacterial population.
Article: Fusidic acid resistance among clinical isolates of methicillin-resistant Staphylococcus aureus in a Taiwanese hospital.[show abstract] [hide abstract]
ABSTRACT: The prevalence of resistance to fusidic acid of methicillin-resistant Staphylococcus aureus (MRSA) was increased each year in a Taiwan hospital. Thirty-four MRSA clinical isolates collected in 2007 and 2008 with reduced susceptibility to FA were selected for further evaluation the presence of resistance determinants. The most common resistance determinant was fusC, found in 25 of the 34 MRSA isolates. One of the 25 fusidic acid-resistant MRSA harboured both fusB and fusC, which is the first time this has been identified. Mutations in fusA were found in 10 strains, a total of 3 amino-acid substitutions in EF-G (fusA gene) were detected. Two substitutions with G556S and R659L were identified for the first time. Low-level resistance to fusidic acid (MICs, ≤32 μg/ml) was found in most our collection. All collected isolates carried type III SCCmec elements. MLST showed the isolates were MRSA ST239. PFGE revealed nine different pulsotypes in one cluster. Our results indicate that the increase in the number of fusidic acid resistant among the MRSA isolates in this hospital is due mainly to the distribution of fusC determinants. Moreover, more than one fusidic acid-resistance mechanism was first detected in a same stain in our collection.BMC Microbiology 01/2011; 11:98. · 3.04 Impact Factor
Article: Fitness of Escherichia coli strains carrying expressed and partially silent IncN and IncP1 plasmids.[show abstract] [hide abstract]
ABSTRACT: Understanding the survival of resistance plasmids in the absence of selective pressure for the antibiotic resistance genes they carry is important for assessing the value of interventions to combat resistant bacteria. Here, several poorly explored questions regarding the fitness impact of IncP1 and IncN broad host range plasmids on their bacterial hosts are examined; namely, whether related plasmids have similar fitness impacts, whether this varies according to host genetic background, and what effect antimicrobial resistance gene silencing has on fitness. For the IncP1 group pairwise in vitro growth competition demonstrated that the fitness cost of plasmid RP1 depends on the host strain. For the IncN group, plasmids R46 and N3 whose sequence is presented for the first time conferred remarkably different fitness costs despite sharing closely related backbone structures, implicating the accessory genes in fitness. Silencing of antimicrobial resistance genes was found to be beneficial for host fitness with RP1 but not for IncN plasmid pVE46. These findings suggest that the fitness impact of a given plasmid on its host cannot be inferred from results obtained with other host-plasmid combinations, even if these are closely related.BMC Microbiology 04/2012; 12:53. · 3.04 Impact Factor
Article: Structure and function of FusB: an elongation factor G-binding fusidic acid resistance protein active in ribosomal translocation and recycling.[show abstract] [hide abstract]
ABSTRACT: Fusidic acid (FA) is a bacteriostatic antibiotic that locks elongation factor G (EF-G) to the ribosome after GTP hydrolysis during elongation and ribosome recycling. The plasmid pUB101-encoded protein FusB causes FA resistance in clinical isolates of Staphylococcus aureus through an interaction with EF-G. Here, we report 1.6 and 2.3 Å crystal structures of FusB. We show that FusB is a two-domain protein lacking homology to known structures, where the N-terminal domain is a four-helix bundle and the C-terminal domain has an alpha/beta fold containing a C4 treble clef zinc finger motif and two loop regions with conserved basic residues. Using hybrid constructs between S. aureus EF-G that binds to FusB and Escherichia coli EF-G that does not, we show that the sequence determinants for FusB recognition reside in domain IV and involve the C-terminal helix of S. aureus EF-G. Further, using kinetic assays in a reconstituted translation system, we demonstrate that FusB can rescue FA inhibition of tRNA translocation as well as ribosome recycling. We propose that FusB rescues S. aureus from FA inhibition by preventing formation or facilitating dissociation of the FA-locked EF-G-ribosome complex.Open biology. 03/2012; 2(3):120016.