Molecular epidemiology, virulence and antimicrobial resistance of Bulgarian methicillin resistant Staphylococcus aureus isolates.

Background: Severe infections of virulent methicillin-resistant Staphylococcus aureus (MRSA) are a serious health problem. The present study aimed to investigate clonal spread, virulence and antimicrobial resistance rates of Bulgarian MRSA isolates in 2016-2020.

Methods: Molecular identification and mecA gene detection were performed with PCR. Clonal relatedness was evaluated by RAPD PCR and MLST. MRSA epidemiology, virulence and resistance patterns were investigated by PCR.

Results: All 27 isolates were identified as S. aureus and were mecA positive, and all were susceptible to linezolid, tigecycline and vancomycin. The toxin genes hlg (in 92.6% of isolates), seb (77.8%), sei (77.8%), seh (59.3%), sej (55.6%), and seg (48.1%), were frequently found among the isolates. Epidemiological typing by RAPD identified 4 clones (16 isolates) and 11 were with a unique profile. MLST analysis of the same MRSA isolates showed five MLST clonal complexes and 11 ST types, including CC5 (33.3%) (ST5, ST221, ST4776), CC8 (22.2%) (ST8, ST239, ST72), CC15 (ST582), CC22 (14.8%) (ST217, ST5417), CC30 (ST30) CC398 (ST398), and CC59 (ST59). The isolates from CC5 showed higher virulence potential and almost all were macrolide resistant (ermB or ermC positive). CC8 isolates showed higher level of resistance.

Conclusion: To the best of our knowledge, this study is the first describing the clonal spreading of Bulgarian MRSA and the association with their virulence and resistance determinants. Monitoring of MRSA epidemiology, resistance and virulence profile can lead to better prevention and faster therapeutic choice in cases of severe infections.