sarA inactivation reduces vancomycin-intermediate and ciprofloxacin resistance expression by Staphylococcus aureus

Abstract

It is known that multiple genome-wide transcriptional changes often accompany the development of antimicrobial resistance and occur in response to challenge with antimicrobial agents. We now show that inactivation of the staphylococcal accessory gene regulator sarA, which controls at least tens of genes in Staphylococcus aureus, leads to dramatic reductions in vancomycin and ciprofloxacin resistance in vancomycin-intermediate and ciprofloxacin-resistant strains of S. aureus. This is particularly evident when judged by antimicrobial-gradient plate analysis or population analysis profiles. Whilst the intact sarA cistron is required for full vancomycin resistance expression by vancomycin-intermediate S. aureus (VISA), sarA expression as determined by real-time polymerase chain reaction was found to be VISA strain-dependent. Reductions in vancomycin resistance expression levels following sarA inactivation do not necessarily include an alteration in autolysis. Expression of sarR, the negative regulator of sarA, was downregulated in two VISA mutants, and transcription of the alternative sigma factor sigB was downregulated in one VISA strain. This study contributes to a growing body of evidence demonstrating the importance of loci previously identified to control virulence in the regulation of clinically relevant antibiotic resistance mechanisms.

The msaABCR Operon Regulates Resistance in Vancomycin-Intermediate Staphylococcus aureus Strains

“…The population analysis profile of the mutant strain displayed a homogeneously sensitive population structure. Similarly, in a study by LamichaneKhadka et al (38), the sarA insertion mutant of BB270V 15 showed a MIC of 3 g/ml in agar dilution analysis, while the wild-type strain showed a vancomycin MIC of 8 g/ml. In the population analysis profile, the mutant displayed a homogeneously sensitive population structure.…”

“…Several studies have demonstrated that global regulators such as sarA and sigB are involved in vancomycin resistance (38,51); however, the mechanism of regulation is not yet understood (26,52). Because msaABCR is a positive regulator of sarA and a negative regulator of autolysis and, as mentioned earlier, both the expression of sarA and a decreased rate of autolysis have been shown to be important for the VISA phenotype, we attempted to understand the effect of the msaABCR operon on vancomycin resistance in VISA strains.…”

“…Collectively, these studies have resulted in a set of phenotypes that are commonly observed in VISA strains. Several studies have also used a variety of approaches to identify specific genes that are associated with vancomycin resistance; these include expression studies (e.g., microarray analysis) (26,27,52) and comparisons of isogenic resistant and sensitive strains in targeted mutagenesis experiments (1,24,32,38,51,64,65). Collectively, these studies have identified the following regulator genes as critical to intermediate vancomycin resistance in S. aureus: pbp4, sigB, walKR, graS, graR, mprF, dltA, vraS, vraR, and sarA.…”

“…Although the mechanism is not yet clear, there is evidence that suppressed autolysis leads to resistance against multiple cell wall-active antibiotics (37). Additionally, in-activation of the sarA gene has been shown to lead to decreases in the vancomycin MICs of laboratory-derived VISA strains (38). These findings led us to investigate the role of the msaABCR operon in the mechanism of resistance of S. aureus strains to cell wall-active antibiotics.…”

Antimicrobial Resistance and Virulence: a Successful or Deleterious Association in the Bacterial World?

“…Several studies have associated the resistance of S. aureus to ciprofloxacin (mutations in DNA gyrase) with the sarA gene regulator (see "Alternative Sigma Factor B " below) (129,130). However, the use of subinhibitory concentrations of ciprofloxacin to treat infections caused by S. aureus strains not only selects for highly resistant strains but also induces the production of virulence factors such as fibronectinbinding proteins, which may promote persistent infection among drug-resistant survivors (131).…”