Strain differentiation in methicillin-resistant Staphylococcus aureus

Area of Science:

• Microbiology
• Infectious Diseases
• Epidemiology

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) is a significant cause of hospital-acquired infections.
• Cross-infection by MRSA poses a substantial challenge in healthcare settings, particularly in New South Wales (NSW).
• Understanding the strain diversity of MRSA is crucial for effective infection control.

Purpose of the Study:

• To determine the strain diversity of MRSA isolates responsible for cross-infections in NSW hospitals.
• To evaluate the utility of biochemical tests and phage typing in differentiating MRSA strains.
• To identify novel phage typing methods for improved MRSA strain characterization.

Main Methods:

• Analysis of 236 MRSA isolates from NSW hospitals.
• Application of biochemical testing methods.
• Phage typing using the Basic International Set of phages at 100x routine test dilution (RTD).
• Isolation and characterization of five new phages for improved typing.

Main Results:

• Biochemical tests provided limited discriminatory power for MRSA strains.
• Phage typing indicated the presence of multiple MRSA strains, with a predominant type (83A/85/95/90/88).
• A significant proportion of isolates were not typable with the standard phage set, and results were often difficult to interpret.
• Newly isolated phages yielded easily identifiable patterns at RTD, enhancing typing accuracy.

Conclusions:

• Multiple MRSA strains contribute to hospital cross-infections in NSW.
• Standard phage typing methods have limitations in characterizing MRSA diversity.
• The development of new phages significantly improves the ability to differentiate and track MRSA strains, aiding infection control efforts.