Antibiotic resistance and biofilm production among the strains of Staphylococcus aureus isolated from pus/wound swab samples in a tertiary care hospital in Nepal

BACKGROUND: The increasing drug resistance along with inducible clindamycin resistance, methicillin resistance and biofilm production among the strains of Staphylococcus aureus are present as the serious problems to the successful treatment of the infections caused by S. aureus. So, the main objectives of this study were to determine the antimicrobial susceptibility patterns along with the rates of inducible clindamycin resistance, methicillin resistance and biofilm production among the strains of S. aureus isolated from pus/wound swab samples. METHODS: A total of 830 non-repeated pus/wound swab samples were processed using standard microbiological techniques. The colonies grown were identified on the basis of colony morphology, Gram’s stain and biochemical tests. Antimicrobial susceptibility testing was performed by Kirby–Bauer disc diffusion technique. Detection of inducible clindamycin resistance was performed by D test, while detection of methicillin resistant S. aureus (MRSA) was performed by determination of minimum inhibitory concentration of oxacillin by agar dilution method. Similarly, detection of biofilm formation was performed by microtiter plate method. Strains showing resistance to three or more than three different classes of antibiotics were considered multidrug resistant. RESULTS: Total 76 samples showed the growth of S. aureus, among which 36 (47.4%) contained MRSA and 17 (22.4%) samples were found to have S. aureus showing inducible clindamycin resistance. Among the S. aureus isolated from outpatients, 41.9% were MRSA. Highest rates of susceptibility of S. aureus were seen toward linezolid (100%) and vancomycin (100%). Similarly, S. aureus isolated from 35 (46.1%) samples were found to be biofilm producers. Higher rate of inducible clindamycin resistance was seen among MRSA in comparison to methicillin susceptible S. aureus (MSSA). Similarly, higher rates of multidrug resistance and methicillin resistance were found among biofilm producing strains in comparison to biofilm non producing strains. CONCLUSIONS: The rate of isolation of MRSA from community acquired infections was found to be high in Nepal. Increased rate of inducible clindamycin resistance as compared to previous studies in Nepal was noted. So for the proper management of the infections caused by S. aureus, D test for the detection of inducible clindamycin resistance should be included in the routine laboratory diagnosis. Further, detection of biofilm production should also be included in the routine tests. Linezolid and vancomycin can be used for the preliminary treatment of the serious infections caused by S. aureus.