Abstract
Background: Methicillin Resistant Staphylococcus aureus (MRSA) has evolved as a serious threat to public health. Objectives: The objectives of the present study were to determine the antibiotics susceptibility patterns of S. aureus and the minimum inhibitory concentration (MIC) of vancomycin to MRSA isolated from different clinical samples at the Colombo South Teaching Hospital (CSTH) in Sri Lanka. Methodology: A total 72 isolates of S. aureus, obtained from different clinical samples at the CSTH, from January to May 2017 were included in the study. S. aureus isolates were identified by Gram stain, colony morphology, catalase, slide/tube coagulase tests. The antibiotic susceptibility tests were carried as per Clinical Laboratory Standards Institute (CLSI) guidelines. MRSA isolates were detected using the cefoxitin (30 μg) disk diffusion test. Inducible clindamycin resistance (MLSB i) was detected by the disk approximation (D test) test. The vancomycin MICs were determined by the E-test method with a 0.5 McFarland standard inoculum. The MIC clinical breakpoints were defined according to the CLSI guidelines (susceptible, ≤2 μg/ml; intermediate, 4–8 μg/ml; and resistant, ≥16 μg/ml). Results: Of the 72 S. aureus clinical isolates, 29 (40.2%) were MRSA. Inducible clindamycin resistance was detected in 16% of the MRSA isolates. Minimum inhibitory concentrations of vancomycin to the isolates of MRSA ranged from 0.125 μg/ml to 2 μg/ml. Conclusions: The rate of isolation of MRSA was high and it has emerged as a serious public health threat to Sri Lanka. The Minimum Inhibitory Concentration (MIC) of all the MRSA isolates were ≤2 μg/ml. None of the MRSA isolates were found to be intermediate-sensitive or vancomycin resistant. Therefore, vancomycin can be used as the drug of choice for treatment of infections caused by MRSA.
Highlights
Methicillin Resistant Staphylococcus aureus (MRSA) has evolved as a serious threat to public health
Inducible clindamycin resistance was detected in 16% of the MRSA isolates
The rate of isolation of MRSA was high and it has emerged as a serious public health threat to Sri Lanka
Summary
Methicillin Resistant Staphylococcus aureus (MRSA) has evolved as a serious threat to public health. Vancomycin is regarded as the drug of choice for the treatment of infections caused by MRSA 4-8. There are some reported cases of treatment failure of the infections caused by MRSA having MIC of vancomycin just below cutoff value. The increasing trends of decreased susceptibility of the strains of MRSA to vancomycin reported from a community study conducted in Sri Lanka, indicated the need of more research in the field. High vancomycin MIC for MRSA which are susceptible to vancomycin may indicate the drug resistance to many antibiotics 13-14. The objectives of the present study were to determine the antibiotics susceptibility patterns of S. aureus and the minimum inhibitory concentration (MIC) of vancomycin to MRSA isolated from different clinical samples at the Colombo South Teaching Hospital (CSTH) in Sri Lanka
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