Minimum Inhibitory Concentration of Vancomycin against Methicillin Resistant Staphylococcus aureus Strains Isolated from a Tertiary Care Hospital DC01-DC05
Dr. Subi Das,
SUJA, C.R. Iyyunni Road, Chembukkavu, Thrissur, Kerala, India.
Introduction: Methicillin Resistant Staphylococcus aureus (MRSA) is one major healthcare associated infection. Prevalence of MRSA and its antibiotic susceptibility changes from time to time. Disc diffusion method remains the most widely used antibiotic susceptibility method in routine clinical laboratories but MIC detection is essential for checking susceptibility to Vancomycin.
Aim: To detect MRSA isolates both by disc diffusion method and Minimum Inhibitory Concentration (MIC) method using E-test, their susceptibility to common antibiotics.
Materials and Methods: A cross-sectional study was conducted on different samples for culture and sensitivity in the microbiology laboratory of a tertiary care centre for six months. Antibiotic susceptibility testing was done in Staphylococcus aureus isolates by disc diffusion method in Mueller Hinton agar. Cefoxitin and Vancomycin MICs of different isolates were detected. Frequencies of MRSA isolates from different clinical samples and their susceptibility to various common antimicrobial agents such as Penicillin (10 units), Cefoxitin (30 μg), Erythromycin (15 μg), Clindamycin (2 μg), Cotrimoxazole (1.25/23.75 μg) and Linezolid (30 μg) were determined. Data were analysed using the IBM SPSS version 23. Descriptive statistics were used.
Results: Total 353 S.aureus isolated over six months period, 100 were Methicillin Resistant (28.3%). A 66% were from males and 34% were from females. MIC50 of Cefoxitin was found to be 16 while the Vancomycin MIC50 was 0.38 and Vancomycin MIC90 was 0.25.
Conclusion: Percentage of MRSA out of S. aureus isolates was 28.3%. Pus swabs were the major sample. All the MRSA isolates had a Vancomycin MIC ≤1.5 μg/mL. E-test has the advantage of detecting even minor changes in MIC.