Characterization of Dutch Staphylococcus aureus from bovine mastitis using a Multiple Locus Variable Number Tandem Repeat Analysis

Current typing methods for Staphylococcus aureus have important drawbacks. We evaluated a Multiple Locus Variable Number Tandem Repeat Analysis (MLVA) scheme with 6 loci which lacks most drawbacks on 85 bovine mastitis isolates from The Netherlands. For each locus the number of repeat units (RU) was calculated. Each combination of repeat units was assigned a MLVA-type (MT). We compared the MLVA typing result with Multi Locus Sequence Typing (MLST), spa-typing and Pulsed-Field Gel Electrophoresis (PFGE). MLVA typing resulted in 18 MTs, although 3 loci could not always be amplified. Spa-typing distinguished 10 spa-types including 3 dominant and 2 new types. PFGE showed 5 dominant profiles with 15 related profiles and 6 unique profiles. MLST showed 4 dominant STs. Some types appeared to be bovine specific. The Simpson's Indices of diversity for PFGE, MLST, spa-typing and MLVA were 0.887, 0.831, 0.69 and 0.781, respectively, indicating that discriminatory power of MLVA was between MLST and spa-typing, whereas PFGE displayed the highest discriminatory power. However, MLVA is fast and cheap when compared to the other methods. The Adjusted Rand index and Wallace's coefficient indicated that MLVA was highly predictive for spa-type, but not vice versa. Analysis of the region neighboring SIRU05 showed a difference in the genetic element bordering the repeats of SIRU05 that explained the negative SIRU05 PCRs. PFGE, MLST, and MLVA are adequate typing methods for bovine-associated S. aureus.