Comparison of MALDI-TOF mass spectrometry with phenotypic methods for identification and characterization of Staphylococcus aureus causing mastitis.

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) infection is one of the greatest threats to both animal and human health. Our investigation was aimed to identify and differentiate between MRSA and methicillin-sensitive Staphylococcus aureus (MSSA) recovered from mastitic milk using MALDI-TOF mass spectrometry compared with phenotypic methods and studying their susceptibility to various antibiotics. Four hundred milk samples from mastitic animals (cows, sheep, goats, and dromedary camels) were investigated. Phenotypic identification of S. aureus was made through MASTASAPH Latex test, STAPH ID 32, and Vitek 2 system. The proteomic characterization of S. aureus was done by MBT. The Kirby Bauer method was accomplished to detect the resistance of S. aureus strains to antibiotics. The results of the MASTASAPH Latex test, revealed that 54 (46%) were recognized as S. aureus. All S. aureus isolates were identified by MBT with a score of more or equal 2.00. Several peaks were identified in the mass of 4590 Da, 4863 Da, and 4938 Da for MSSA and in the mass of 2636 Da and 3009 Da for MRSA. The MSP dendrogram demonstrated that the S. aureus isolates were classified into one group with a distance level of less or equal 400. The percentage of S. aureus resistance against carbenicillin, erythromycin and kanamycin was 94.4%, 38.88%, and 33.33%, respectively. In conclusion, S. aureus bacteria are among the key triggers for mastitis in Saudi Arabia. MBT is reported to be not only the rapid tool to identify S. aureus but also able to discriminate MRSA from MSSA.