Novel Mutation Sites in the Development of Vancomycin- Intermediate Resistance in Staphylococcus aureus

Abstract

Increased use of vancomycin has led to the emergence of vancomycin-intermediate Staphylococcus aureus (VISA). To investigate the mechanism of VISA development, 39 methicillin-susceptible strains and 3 MRSA strains were treated with vancomycin to induce non-susceptibility, and mutations in six genes were analyzed. All the strains were treated with vancomycin in vitro for 60 days. MICs were determined by the agar dilution and E-test methods. Vancomycin was then removed to assess the stability of VISA strains and mutations. Following 60 days of vancomycin treatment in vitro, 29/42 VISA strains were generated. The complete sequences of rpoB, vraS, graR, graS, walK, and walR were compared with those in the parental strains. Seven missense mutations including four novel mutations (L466S in rpoB, R232K in graS, I594M in walk, and A111T in walR) were detected frequently in strains with vancomycin MIC ≥ 12 μg/mL. Jonckheere-Terpstra trend test indicated these mutations might play an important role during VISA evolution. After the vancomycin treatment, strains were passaged to vancomycin-free medium for another 60 days, and the MICs of all strains decreased. Our results suggest that rpoB, graS, walk, and walR are more important than vraS and graR in VISA development.

Education to improve vancomycin use: the perspectives of educators and education recipients

“…Suboptimal dosing practices can result in treatment failure or toxicity . Furthermore, inappropriate dosing practices have accelerated the development of resistant strains, and consequently, vancomycin is becoming a less‐effective treatment option …”

Phenotypic Plasticity of Staphylococcus aureus in Liquid Medium Containing Vancomycin

“…The growth curves of untreated and 2 μg/ml vancomycin-treated cells were plotted to test the growth plasticity of S. aureus in vancomycin (Figures 1A,B). In total, 41 strains (S1’–S9’ and S11’–S42’) were obtained by 60-day in vitro vancomycin treatment in our previous study (Wang et al, 2016). In the absence of antibiotics, 40 S. aureus strains grew well, but S6’ grew slowly and had a modest exponential period.…”

“…All S. aureus strains were obtained by 60-day in vitro vancomycin treatment in our previous study (Wang et al, 2016). Strains’ background is listed in Supplementary Table S1; 41 parental strains from 12 sequence types were treated with vancomycin for 60 days as described (Wang et al, 2016).…”

“…All S. aureus strains were obtained by 60-day in vitro vancomycin treatment in our previous study (Wang et al, 2016). Strains’ background is listed in Supplementary Table S1; 41 parental strains from 12 sequence types were treated with vancomycin for 60 days as described (Wang et al, 2016). Each parental strain (S1–S9 and S11–S42) was incubated on brain heart infusion (BHI) (Oxoid, Basingstoke, United Kingdom) agar plates with vancomycin (Sigma–Aldrich, St. Louis, MO, United States) of 50% initial minimum inhibitory concentration (MIC) at 37°.…”

Synergistic Potential of Antimicrobial Combinations Against Methicillin-Resistant Staphylococcus aureus

“…In addition, recently, a new theory of collateral susceptibility in antimicrobial agents may inspire a novel insight for the synergism of vancomycin combined with oxacillin. Previous studies reported the oxacillin MICs of S. aureus strains decreased after vancomycin treatment (Wang et al, 2017), so called "see-saw phenomenon" occurring in certain stages of vancomycin resistance promotion, suggesting that upon acquisition of vancomycin resistance or VISA evolution, some strains show a concomitant decrease in oxacillin resistance (Bhateja et al, 2006). It was reported that mutated graR may impair oxacillin resistance (Neoh et al, 2008).…”