Antimicrobial resistance and the prevalence of the Panton-Valentine Leukocidin gene among clinical isolates of Staphylococcus aureus in Lithuania

Abstract

Abstract Background Staphylococcus aureus is one of the most frequently identified pathogens causing nosocomial infections worldwide and, in many cases, exhibits resistance to multiple antimicrobials. However, there is a lack of data about the prevalence of S. aureus resistance to antimicrobials in major hospitals in Vilnius city, Lithuania. Therefore, the aim of this study was to determine the resistance to antimicrobials of Staphylococcus aureus strains isolated from clinical specimens in Lithuanian hospitals and to identify the genes conferring resistance and virulence. Methods This study was carried out from June 2019 to September 2021. S. aureus strains were isolated from clinical specimens. Antibiotic susceptibility testing was performed by the disc diffusion method according to EUCAST guidelines. All our collected isolates were analysed 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. Results A total of 745 S. aureus strains isolated from clinical specimens were analysed. A total of 69.0% of strains were isolated from the skin and soft tissues, 14.5% from blood, 11.7% from the lower respiratory tract, 2.7% from urine and 2.1% from other specimens. Antimicrobial susceptibility testing revealed that all 745 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 to 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 the 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. A total of 69.2% of tetracycline-resistant S. aureus strains had the tetK gene, and 28.2% had the tetM gene. A total of 7.3% of S. aureus isolates harboured the lukF-PV gene. The frequency of pvl gene detection was significantly higher in the MRSA isolates than in the methicillin-susceptible S. aureus (MSSA) isolates (p < 0.0001). Conclusions All tested strains were susceptible to rifampicin and vancomycin. A total of 6% of the strains were MRSA. The lowest susceptibility rate was found to penicillin. The tetK gene was predominant among S. aureus strains resistant to tetracycline, and the ermC gene was predominant among erythromycin-resistant strains. Seven percent of S. aureus isolates harboured the lukF-PV gene, which was more prevalent in methicillin-resistant strains.