Evaluation of electrophoretic methods for typing methicillin-resistant Staphylococcus aureus

Area of Science:

• Microbiology
• Epidemiology
• Molecular Typing

Background:

• Accurate typing of methicillin-resistant Staphylococcus aureus (MRSA) is crucial for epidemiological surveillance and outbreak investigation.
• Established methods like phage typing have limitations in discriminating between closely related MRSA strains.

Purpose of the Study:

• To evaluate and compare the discriminatory power and interpretability of three electrophoretic typing methods for MRSA: plasmid profiles (PP), whole-cell protein profiles (WCPP), and immunoblotting profiles (IP).
• To assess the consistency and comparability of these methods with traditional phage typing in outbreak settings.

Main Methods:

• Plasmid profiles (PP), whole-cell protein profiles (WCPP), and immunoblotting profiles (IP) were performed on MRSA isolates from 12 outbreaks.
• Results were compared within and between outbreaks to assess consistency.
• Comparison was also made against established phage typing results and a reference London epidemic MRSA strain.

Main Results:

• Good overall agreement was observed between the four typing methods, though concordance varied across outbreaks.
• Whole-cell protein profiles (WCPP) showed more bands and subtle differences than phage typing, while immunoblotting profiles (IP) had fewer, more easily interpretable bands.
• Phage typing and WCPP demonstrated the highest discriminatory power when comparing index strains and the London epidemic MRSA strain, yielding nine distinct patterns each.

Conclusions:

• Both whole-cell protein profiles (WCPP) and immunoblotting profiles (IP) provide valuable epidemiological data for MRSA.
• Immunoblotting profiles (IP) are the most straightforward electrophoretic method to interpret for MRSA strain typing.
• Electrophoretic methods offer complementary information to phage typing, particularly for detecting minor strain variations.