Antimicrobial Resistance and the Prevalence of the Panton-Valentine Leukocidin Gene among Clinical Isolates of Staphylococcus aureus in Lithuania

This study aimed to determine resistance to antimicrobials of Staphylococcus aureus strains isolated from clinical specimens in Lithuanian hospitals and to identify the genes conferring resistance and virulence. The study was carried out from June 2019 to September 2021. S. aureus strains were isolated from skin, soft tissues, blood, lower respiratory tract, urine and other specimens. Antibiotic susceptibility testing was performed using the disc diffusion method according to EUCAST guidelines. All isolates were analyzed for detection of the ermA, ermC, mecA, mecC, tetK, tetM, and lukF-PV genes by multiplex real-time PCR. The 16S rRNA coding sequence was applied as an internal PCR control. Altogether, 745 S. aureus strains were analyzed. Antimicrobial susceptibility testing revealed that all isolates were susceptible to rifampin and vancomycin. Of the 745 strains, 94.8% were susceptible to tetracycline, 94.5% to clindamycin, and 88.3% to erythromycin. The lowest susceptibility rate was found for penicillin (25.8%). Six percent of the tested strains were methicillin-resistant S. aureus (MRSA). The majority of methicillin-resistant strains were isolated from skin and soft tissues (73.3%), with a smaller portion isolated from blood (17.8%) and respiratory tract (8.9%). The ermC gene was detected in 41.1% of erythromycin-resistant S. aureus strains, whereas ermA was detected in 32.2% of erythromycin-resistant S. aureus strains. 69.2% of tetracycline-resistant S. aureus strains had tetK gene, and 28.2% had tetM gene. 7.3% of S. aureus isolates harbored lukF-PV gene. The frequency of the pvl gene detection was significantly higher in MRSA isolates than in methicillin-susceptible S. aureus isolates (p < 0.0001).