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Minimum Inhibitory Concentrations of Vancomycin and Daptomycin Against Methicillin-resistant Staphylococcus Aureus

Vinay Kumar Moses1, Venkataramana Kandi2, Sanjeev Kumar D Rao3

  • 1Microbiology, Government Medical College, Siddipet, IND.

Cureus
|March 7, 2020
PubMed

Insights

Methicillin-resistant Staphylococcus aureus (MRSA) infections show rising vancomycin resistance, with many strains becoming vancomycin-intermediate sensitive Staphylococcus aureus (VISA). Daptomycin remains effective against all tested MRSA strains, offering a viable treatment option.

Area of Science:

  • Microbiology
  • Infectious Diseases
  • Clinical Pharmacy

Background:

  • Staphylococci, including Staphylococcus aureus (S. aureus), are common human and animal colonizers.
  • S. aureus causes various infections and is transmitted easily, leading to hospital- and community-associated infections.
  • Methicillin-resistant S. aureus (MRSA) presents treatment challenges, with vancomycin as a primary choice, but vancomycin-intermediate sensitive S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA) are emerging.

Purpose of the Study:

  • To evaluate the minimum inhibitory concentrations (MICs) of vancomycin and daptomycin against MRSA strains.
  • To assess the prevalence of vancomycin resistance and intermediate sensitivity in MRSA isolates from clinical specimens.

Main Methods:

  • Analysis of 115 MRSA isolates collected over 26 months (July 2010-September 2012) from various human clinical specimens.
  • Confirmation of MRSA using the Kirby-Bauer disk diffusion method with cefoxitin.
  • Determination of vancomycin and daptomycin MICs using agar dilution and E-test methods, respectively, following CLSI guidelines.

Main Results:

  • Out of 115 S. aureus isolates, 7 (6.08%) were VRSA and 53 (46.08%) were VISA based on new CLSI breakpoints.
  • Daptomycin showed an MIC of ≤1 µg/ml for all tested MRSA isolates, indicating consistent effectiveness.

Conclusions:

  • A concerning trend of increasing vancomycin MICs among MRSA isolates was observed.
  • A significant proportion of MRSA strains exhibited intermediate sensitivity to vancomycin (VISA).
  • Daptomycin demonstrated universal effectiveness against the studied MRSA isolates, highlighting its potential as an alternative treatment.
Keywords:
daptomycinmethicillin-resistant staphylococcus aureusminimum inhibitory concentration (mic)mrsas. aureusstaphylococcus aureusvancomycin

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