Vancomycin Activates σB in Vancomycin-Resistant Staphylococcus aureus Resulting in the Enhancement of Cytotoxicity

Abstract

The alternative transcription factor σB is responsible for transcription in Staphylococcus aureus during the stress response. Many virulence-associated genes are directly or indirectly regulated by σB. We hypothesized that treatment with antibiotics may act as an environmental stressor that induces σB activity in antibiotic-resistant strains. Several antibiotics with distinct modes of action, including ampicillin (12 µg/ml), vancomycin (16 or 32 µg/ml), chloramphenicol (15 µg/ml), ciprofloxacin (0.25 µg/ml), and sulfamethoxazole/trimethoprim (SXT, 0.8 µg/ml), were investigated for their ability to activate this transcription factor. We were especially interested in the stress response in vancomycin-resistant S. aureus (VRSA) strains treated with vancomycin. The transcription levels of selected genes associated with virulence were also measured. Real-time quantitative reverse transcription PCR was employed to evaluate gene transcription levels. Contact hemolytic and cytotoxicity assays were used to evaluate cell damage following antibiotic treatment. Antibiotics that target the cell wall (vancomycin and ampicillin) and SXT induced σB activity in VRSA strains. Expression of σB-regulated virulence genes, including hla and fnbA, was associated with the vancomycin-induced σB activity in VRSA strains and the increase in cytotoxicity upon vancomycin treatment. These effects were not observed in the sigB-deficient strain but were observed in the complemented strain. We demonstrate that sub-minimum inhibitory concentration (sub-MIC) levels of antibiotics act as environmental stressors and activate the stress response sigma factor, σB. The improper use of antibiotics may alter the expression of virulence factors through the activation of σB in drug-resistant strains of S. aureus and lead to worse clinical outcomes.

Modulation of Staphylococcus aureus Biofilm Matrix by Subinhibitory Concentrations of Clindamycin

“…As subinhibitory concentrations of antibiotics can induce a general stress response (38,55), gene expression of the alternative sigma factor B ( B ) was investigated in our biofilm model and showed an upregulation of 3-and 7-fold in response to 0.03 and 0.06 g/ml clindamycin, respectively (Fig. 3B).…”

Knockout of Extracytoplasmic Function Sigma Factor ECF-10 Affects Stress Resistance and Biofilm Formation in Pseudomonas putida KT2440

“…Since recent studies have demonstrated a role for ECF sigma factors in antibiotic resistance (36,37), we investigated the impact of the ECF-10 sigma factor knockout on the susceptibility of P. putida KT2440 to different classes of antibiotics. As shown in Table 2, the ECF-10 mutant exhibited a 2-to 4-fold increase in resistance to ciprofloxacin, meropenem, chloramphenicol, nalidixic acid, and sulfamethoxazole compared to that of the wild-type strain.…”

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

“…In S. aureus, alternative sigma factor B controls the expression of multiple genes, including virulence determinants such as ␣-hemolysin (encoded by hla), fibronectin-binding protein A (encoded by fnbA), and global regulators (SarA and/or Agr locus); it also promotes capsule production (395) and increases the resistance levels of methicillinresistant S. aureus (MRSA) and glycopeptide-intermediate S. aureus (GISA) strains (396,397). It has recently been shown that inactivation of the staphylococcal factor B -controlled yabJspoVG operon, which codes for B. subtilis YabJ and SpoVG sequence homologs, significantly reduces the level of transcription of the cap operon and impedes capsule formation in capsular polysaccharide-producing strains (398).…”