AUTHOR=Wang Yubing , Li Xiaoli , Jiang Libo , Han Wentao , Xie Xiangming , Jin Yi , He Xiaoqing , Wu Rongling 

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

JOURNAL=Frontiers in Microbiology

VOLUME=7

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2016.02163

DOI=10.3389/fmicb.2016.02163

ISSN=1664-302X

ABSTRACT=<p>Increased use of vancomycin has led to the emergence of vancomycin-intermediate <italic>Staphylococcus aureus</italic> (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 <italic>in vitro</italic> for 60 days. MICs were determined by the agar dilution and <italic>E</italic>-test methods. Vancomycin was then removed to assess the stability of VISA strains and mutations. Following 60 days of vancomycin treatment <italic>in vitro</italic>, 29/42 VISA strains were generated. The complete sequences of <italic>rpoB, vraS, graR, graS, walK</italic>, and <italic>walR</italic> were compared with those in the parental strains. Seven missense mutations including four novel mutations (L466S in <italic>rpoB</italic>, R232K in <italic>graS</italic>, I594M in <italic>walk</italic>, and A111T in <italic>walR</italic>) 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 <italic>rpoB, graS, walk</italic>, and <italic>walR</italic> are more important than <italic>vraS</italic> and <italic>graR</italic> in VISA development.</p>