Dynamics of Staphylococcus Aureus Antibiotic Resistance to Fluoroquinolones in Vitro

Introduction. S. aureus is the main pathogen of skin, soft tissues and otorhinolaryngological infections as well as the cause of osteomyelitis, meningitis and endocarditis. In recent years the importance of S. aureus mediated infections has grown not only because of their spreading, but also due to their antibiotic resistance. Recent obser­vations showed that the resistance is developed to each new antibacterial agent after 5 years of its intensive use. Based on the studies conducted in Ukraine, it is known that the resistance of S. aureus to fluoroquinolones varies in different regions and ranges from 4.00-6.00 % to gatifloxacin to 45.20-49.00 % to norfloxacin and pefloxacin. Considering that in the overwhelming majority of cases antibacterials are prescribed empirically, an important background for successful antibiotic therapy is taking into account the regional and mostly the local antimicrobial resistance patterns. The aim of the study was to evaluate the antibiotic resistance profile of S. aureus isolates to fluoroquinolones and its changing during 2011-2016. Materials and methods. 355 S. aureus strains isolated from adult patients who were treated in Uzhgorod med­ical institutions due to bacterial tonsillitis or pharyngitis during 2011-2016 were included in the study. After isolation of a pure culture, susceptibilities were tested by using the disk diffusion method. The following antimicrobial disks were tested on Muller-Hinton agar (Biolife, Italy): ofloxacin (5.0 pg), ciprofloxacin (5.0 pg), levofloxacin (5.0 pg), gatifloxacin (5.0 pg), Sparfloxacin (10.0 pg), pefloxacin (10.0 pg), and norfloxacin (10.0 pg). Research methods were used with respect for human rights, according to the current legislation in Ukraine in accordance to international ethical requirements and do not violate the ethical standards in science and standards for conducting biomedical research. Results. Analysis of S. aureus resistance to fluoroquinolones found that this parameter remained at a relatively low level and, in majority of cases, did not exceed 12.00 %. However, constant increasement of antimicrobial re­sistance was noticed during 2011-2016. Thus, the S. aureus resistance to norfloxacin, levofloxacin and ciprofloxacin increased significantly from 0.00 %, 0.00 % and 1.54 % in 2011 to 11.76 %, 13.73 % and 9.80 % in 2016 respec­tively. Resistance to ofloxacin and gatifloxacin in 2011-2016 rised from 3.08 % and 0.00 % to 11.76 % and 1.96 %, respectively, but this difference was not statistically significant. The S. aureus susceptibility to fluoroquinolones fluctuated within 80.00-90.00 % during 2011-2016 and gradually decreased. For instance, susceptibility to norfloxacin, ofloxacin and levofloxacin decreased significantly from 93.85 %, 96.92 % and 100.00 % to 80.39 %, 88.24 % and 84.31 % respectively over the past 6 years. However, for pefloxacin there was a significant increase in susceptibili­ty from 90.77 % to 100.00 % during the investigated period. The prevalence rates of intermediate resistant S. aureus isolates during the study period was negligible and in majority of cases this type of strains were not detected at all. Conclusions. Relatively low rates of resistance and high rates of susceptibility allowed to recommend fluoro­quinolones for the empirical therapy of S. aureus caused infections. However, the gradual increase of resistance to these antibiotics, requires strict compliance with the antimicrobial stewardship