Sequence-Based spa Typing as a Rapid Screening Method for the Areal and Nosocomial Outbreaks of MRSA

Methicillin-resistant Staphylococcus aureus (MRSA) is the leading cause of nosocomial infection and MRSA outbreaks have become a major problem. Therefore, the rapid and accurate typing of MRSA isolates is important for epidemiological surveys and nosocomial infection control. Pulsed-field gel electrophoresis (PFGE) is considered as the gold standard technique for MRSA typing, because of its high discriminatory power, but its procedure is rather complicated and time-consuming. The spa gene encodes a cell wall component of Staphylococcus aureus protein A, and exhibits polymorphism. Sequencing the spa gene is expected superior to PFGE in speed and data interpretation. In the present study, we evaluated whether spa typing of MRSA is useful for nosocomial outbreak analysis and epidemiological investigations. We analyzed 19 nosocomial outbreak isolates from 4 separate hospitals and 26 isolates from outpatients of Toyama University Hospital. Either PFGE or spa typing revealed a single nosocomial strain that appears unique to each hospital. Indeed, spa typing confirmed the four different strains, but PFGE demonstrated only 3 strains. With the total 45 isolates, PFGE showed 16 different patterns and spa typing showed 12 patterns. Moreover, we were able to analyze the spa gene in about 2 days, from sampling to obtaining the results, whereas it took about 7 days with PFGE. In conclusion, sequence-based spa typing shows comparable sensitivities to PFGE, and is a rapid and easy handling method. The sequence-based spa typing can be used as the rapid screening test when MRSA outbreak is suspected in areas and hospitals.