Plasmid pattern analysis of Staphylococcus species isolated from bovine mammary secretions

Plasmid profiles of staphylococci isolated from bovine mammary secretions were heterogeneous as shown by the study of 94 isolates representing six species. Plasmids were identified in 19 of 94 staphylococcal isolates. Number of plasmids per isolate varied from 1 to 4. Size of plasmids ranged from 1.2 to 45 MDa; however, most were between 1.8 and 4.8 MDa. Some isolates with identical plasmid profiles were observed within and between species. Plasmid profiles observed in this study suggest that no specific plasmid pattern occurs within a species. Ability to differentiate isolates was not enhanced when antibiograms were used in conjunction with plasmid profiles. Plasmid pattern analysis does not appear to be an adequate method for discriminating between isolates of a species and would likely provide limited epidemiological information regarding staphylococci of bovine origin.