Synergistic Effects of Antibiotic Combinations against Staphylococcus aureus in Clinical Samples from Inpatients at a Tertiary Care Facility in Hyderabad, India

Abstract

Background Staphylococcus aureus infections are commonly caused by bacteria in community and hospital settings. The basis of modern medicine is at risk due to the worldwide problem of antibiotic resistance and the need to discover viable antimicrobials. One way to tackle antibiotic resistance (AMR) is by combination therapy. Due to their promising efficacy against bacteria, the current research focuses on combining antibiotics. Objective This study aimed to study the synergistic effects of antibiotic combinations against Staphylococcus aureus from clinical samples of inpatients at a tertiary care hospital in Hyderabad, India Materials and Methods Staphylococcus aureus (S. aureus) was isolated from the in-house clinical samples and was further subjected to antimicrobial susceptibility testing. Minimum Inhibitory Concentration (MIC) by broth microdilution method was determined against four antimicrobials. Biofilm formation and time-kill analysis were performed for combination antibiotics. The checkerboard test for fractional inhibition (FIC) was used to evaluate the synergistic effect of both agent combinations. Results A total of 3663 clinical samples, with 185 identified as S. aureus. Methicillin-resistant S. aureus (MRSA) were confirmed by phenotypic and genotypic methods showing positive for 84 isolates (45\%). The prevalence was high in male patients at 51\% and in the critical care wards at 30\%, and blood samples scoring 43\%. The highest antibiotic resistance was against the cephalosporin group, followed by quinolones and macrolides. The MIC results showed that amikacin and azithromycin had a value of 4 µg/ ml, whereas levofloxacin MIC was 2 µg/ ml. FIC concentration with a borderline of ≤ 0.5 showed synergistic activity against MRSA strains with a combination of amikacin and levofloxacin. Conclusion An antibiotic combination therapy of amikacin and levofloxacin produces a synergistic effect against MRSA, thereby significantly increasing anti-biofilm efficacy and feasibility of preventing or delaying the formation of resistance.