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

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Rising vancomycin use has driven the emergence of vancomycin-intermediate Staphylococcus aureus (VISA).
• Understanding the genetic mechanisms underlying VISA development is critical for combating antibiotic resistance.

Purpose of the Study:

• To investigate the genetic mutations associated with the development of vancomycin intermediate resistance in Staphylococcus aureus.
• To identify key genes involved in the in vitro induction and evolution of VISA.

Main Methods:

• Induction of vancomycin non-susceptibility in methicillin-susceptible and resistant Staphylococcus aureus strains through 60-day in vitro vancomycin treatment.
• Determination of Minimum Inhibitory Concentrations (MICs) using agar dilution and E-test methods.
• Sequencing of six key genes (rpoB, vraS, graR, graS, walK, walR) to identify mutations in VISA strains.

Main Results:

• Twenty-nine out of 42 induced strains developed vancomycin intermediate resistance (MIC ≥ 12 μg/mL).
• Seven missense mutations, including four novel ones (in rpoB, graS, walK, and walR), were frequently detected in VISA strains.
• Mutations in rpoB, graS, walK, and walR were identified as more significant in VISA development compared to vraS and graR.

Conclusions:

• Specific mutations in rpoB, graS, walK, and walR play a significant role in the development and evolution of vancomycin intermediate resistance in Staphylococcus aureus.
• The identified mutations contribute to VISA phenotypes but are not fully stable upon removal of vancomycin pressure.