Verification of molecular characterization of coagulase positive Staphylococcus from bovine mastitis with matrix-assisted laser desorption ionization, time-offlight mass spectrometry (MALDI-TOF MS) mass spectrometry

Besides Staphylococcus aureus, other coagulase-positive Staphylococcus (CPS) species such as Staphylococcus hyicus and Staphylococcus intermedius are implicated in bovine mastitis etiology. These species are often misdiagnosed as S. aureus. Also, some atypical S. aureus isolates can test negative for coagulase production and consequently be misdiagnosed as coagulase-negative Staphylococcus (CNS). Several currently available methods for the identification of Staphylococcus spp., including molecular techniques, are widely used worldwide. Recently, matrix-assisted laser desorption ionization, time-offlight mass spectrometry (MALDI-TOF MS) has been attracting attention for its fast and precise identification of several microorganisms at the species level. The present work evaluated the efficiency of a protocol for S. aureus characterization using PCR and M-PCR procedures. MALDI-TOF was considered the gold standard test to evaluate the sensitivity and specificity of the proposed identification protocol. Seventy-two Staphylococcus spp., isolates were evaluated. All samples were submitted to PCR for coa, nuc and 23S rDNA. Out of 33 isolates, genotypically charac-terized as S. aureus and confirmed by MALDI-TOF MS, 2 (6.1%) tested negative for coagulase production. Three isolates were identified as S. hyicus (2) and S. intermedius (1) by MALDI-TOF MS. The proposed molecular identification schedule achieved 100% sensitivity and specificity as compared to MALDI-TOF MS.