Evaluation of an antibiogram-resistogram typing scheme for methicillin-resistant Staphylococcus aureus

Area of Science:

• Clinical Microbiology
• Infectious Diseases
• Hospital Epidemiology

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant threat in healthcare settings.
• Effective strain typing is crucial for controlling MRSA transmission and outbreaks.
• Existing typing methods may have limitations in speed or discriminatory power.

Purpose of the Study:

• To evaluate the utility of an antibiogram-resistogram (AR) typing scheme for characterizing MRSA populations.
• To assess the scheme's ability to differentiate MRSA strains during a defined study period in a hospital group.
• To determine if AR typing can identify specific outbreaks and track strain importation.

Main Methods:

• A modified Stokes' disk diffusion technique was used to determine AR patterns for 22 antibiotics and chemicals.
• MRSA isolates collected between December 1992 and August 1993 were analyzed.
• AR patterns were compared with phage typing, plasmid profiling, and restriction endonuclease analysis.

Main Results:

• The AR typing scheme classified the MRSA population into 31 types, with 90% belonging to seven common types.
• The most frequent types (AR 13 and 14) were distinguishable only by lincomycin/clindamycin susceptibility.
• AR typing revealed variations in type incidence across hospitals and over time, and identified specific outbreaks and imported strains.

Conclusions:

• The AR typing scheme is a valuable tool for differentiating MRSA strains in a clinical laboratory setting.
• The method provides rapid results (within 24 hours) and can distinguish between local and imported MRSA strains.
• AR typing aids in understanding MRSA epidemiology, including outbreak detection and strain surveillance.