Species-level identification of staphylococci isolated from bovine mastitis in Brazil using partial 16S rRNA sequencing

- 95% of the Staphylococcus spp. isolates were identified at the species level.
- Thirteen different Staphylococcus species were identified.
- S. chromogenes, S. aureus and S. epidermidis were identified most frequently.
- The species S. agnetis and S. devriesei were identified in the present study.
- Six coagulase-negative S. aureus isolates were identified in the present study.

Staphylococci isolated from bovine milk and not classified as Staphylococcus aureus represent a heterogeneous group of microorganisms that are frequently associated with bovine mastitis. The identification of these microorganisms is important, although it is difficult and relatively costly. Genotypic methods add precision in the identification of Staphylococcus species. In the present study, partial 16S rRNA sequencing was used for the species identification of coagulase-positive and coagulase-negative staphylococci isolated from bovine mastitis. Two hundred and two (95%) of the 213 isolates were successfully identified at the species level. The assigning of an isolate to a particular species was based on ≥99% identity with 16S rRNA sequences deposited in GenBank. The identified isolates belonged to 13 different Staphylococcus species; Staphylococcus chromogenes, S. aureus and Staphylococcus epidermidis were the most frequently identified species. Eight isolates could not be assigned to a single species, as the obtained sequences showed 99% or 100% similarity to sequences from two or three different Staphylococcus species. The relatedness of these isolates with the other isolates and reference strains was visualized using a cladogram. In conclusion, 16S rRNA sequencing was an objective and accurate method for the proper identification of Staphylococcus species isolated from bovine mastitis. Additional target genes could be used in non-conclusive cases for the species-level identification of these microorganisms.