Multiple-locus variable number tandem repeat analysis is superior to spa typing and sufficient to characterize MRSA for surveillance purposes

Aim: Assess the best approach to type methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcal protein A (spa) typing, multiple-locus variable number tandem repeat analysis (MLVA) or both. Materials & methods: Discriminatory power of spa typing and MLVA was determined using 20,771 MRSA isolates. Results: There were twice as many MLVA types (MTs) as spa types present in the collection. Among the top 70% of the isolates, 37 spa types and 139 MTs were found. MLVA diversity among the top-10 spa types was high (diversity index 0.96), while spa diversity among the top-10 MTs was much lower (diversity index 0.83). The probability that two MRSA isolates with the same spa type also had the same MT was low (Wallace's coefficient 0.27). By contrast, most MRSA isolates yielding the same MT also had the same spa type (Wallace's coefficient 0.90). Conclusion: MLVA is superior to spa typing and will suffice to characterize MRSA isolates for surveillance.