Application of pulsed-field gel electrophoresis and binary typing as toolsin veterinary clinical microbiology and molecular epidemiologic analysis of bovine and human Staphylococcus aureus isolates

Thirty-eight bovine mammary Staphylococcus aureus isolates from diverse cli nical, temporal, and geographical origins were genotyped by pulsed-field ge l electrophoresis (PFGE) after SmaI digestion of prokaryotic DNA and by mea ns of binary typing using 15 strain-specific DNA probes. Seven pulsed-field types and four subtypes were identified, as were 16 binary types. Concorda nt delineation of genetic relatedness was documented by both techniques, ye t based on practical and epidemiological considerations, binary typing was the preferable method. Genotypes of bovine isolates were compared to 55 pre viously characterized human S. aureus isolates through cluster analysis of binary types. Genetic clusters containing strains of both human and bovine origin were found, but bacterial genotypes were predominantly associated wi th a single host species. Binary typing proved an excellent tool for compar ison of S. aureus strains, including methicillin-resistant S. aureus, deriv ed from different host species and from different databases. For 28 bovine S. aureus isolates, detailed clinical observations in vivo were compared to strain typing results in vitro, Associations were found between distinct g enotypes and severity of disease, suggesting strain-specific bacterial viru lence. Circumstantial evidence furthermore supports strain-specific routes of bacterial dissemination. We conclude that PFGE and binary typing can be successfully applied for genetic analysis of S. aureus isolates from bovine mammary secretions. Binary typing in particular is a robust and simple met hod and promises to become a powerful tool for strain characterization, for resolution of clonal relationships of bacteria within and between host spe cies, and for identification of sources and transmission routes of bovine S . aureus.