Original article / research
In-vitro Susceptibility of Linezolid and Teicoplanin in Methicillin-resistant Staphylococcus aureus by E-test
Dr. Burle Gowtham,
Senior Resident, Department of Microbiology, NRI Institute of Medical Sciences, Sangivalasa, Visakhapatnam, Andhra Pradesh, India.
Introduction: Staphylococcus aureus (S. aureus) is a ubiquitous pathogen causing various infections in humans. The emergence of drug resistance in S. aureus, especially methicillin resistance, has made treating these infections increasingly tricky, with only a few antibiotics being effective. Vancomycin, teicoplanin, and linezolid are the antibiotics of choice for treating Methicillin-resistant Staphylococcus aureus (MRSA) infections, though occasional resistance to these antibiotics has also been reported.
Aim: To know the prevalence of MRSA and subject the MRSA isolates to linezolid and teicoplanin susceptibility testing by Epsilometer test (E-test).
Materials and Methods: This was a cross-sectional study done between April 2021 to March 2022. A total of 210 consecutive S. aureus isolates from various clinical samples were isolated and processed in the Department of Microbiology, Andhra Medical College, Visakhapatnam, Andhra Pradesh, India. Screening for methicillin resistance was done by cefoxitin disc diffusion testing and Chromogenic agar (CHROMagar) MRSA, with American Type Culture Collection (ATCC) S. aureus 25923 strain as a negative control and a known inhouse strain was used as a positive control. All the MRSA isolates were tested for linezolid and teicoplanin susceptibility for the E-test to determine the Minimum Inhibitory Concentration (MIC). Data were entered into Microsoft excel 2019, and International Business Machines (IBM) Statistical Package for the Social Sciences (SPSS) version 20.0 was used for analysis.
Results: Out of 210 S. aureus, 100 (47.6%) were MRSA isolates. MRSA was predominantly isolated from pus (58%), sputum (19%) and urine (9%) samples. Higher resistance was observed against cotrimoxazole (72%), ciprofloxacin (54%) and amikacin (37%). Teicoplanin and linezolid were both susceptible in all of the isolates. MIC50 and MIC90 against linezolid and teicoplanin was 0.5 and 1 mcg/mL and 0.5 and 0.75 μg/mL respectively.
Conclusion: The MRSA isolates are increasingly becoming resistant to multiple antibiotics. Linezolid and glycopeptides are still the mainstays for treating MRSA infections, as most isolates are susceptible to these drugs.
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