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Year : 2003  |  Volume : 21  |  Issue : 4  |  Page : 289--290

In vitro activity of linezolid in staphylococcus aureus

N Gupta, Aparna, S Saini, B Kumar, DR Arora 
 Department of Microbiology, Pt. BD Sharma Post Graduate Institute of Medical Sciences, Rohtak - 124 001, Haryana, India

Correspondence Address:
D R Arora
Department of Microbiology, Pt. BD Sharma Post Graduate Institute of Medical Sciences, Rohtak - 124 001, Haryana

How to cite this article:
Gupta N, Aparna, Saini S, Kumar B, Arora D R. In vitro activity of linezolid in staphylococcus aureus.Indian J Med Microbiol 2003;21:289-290

How to cite this URL:
Gupta N, Aparna, Saini S, Kumar B, Arora D R. In vitro activity of linezolid in staphylococcus aureus. Indian J Med Microbiol [serial online] 2003 [cited 2021 Jan 22 ];21:289-290
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Dear Editor,

Linezolid is the first drug of a new class of antibiotics, the oxazolidinones, introduced recently to therapy.[1] Linezolid, unlike other protein synthesis inhibitors, acts early in translation by disrupting the interaction of formyl-methionine transfer RNA with the 50S ribosomal subunit during formation of the pre-initiation complex.[2] The aim of this study was to investigate the in vitro activity of linezolid against Staphylococcus aureus isolated from patients suffering from various community and hospital acquired infections.

A total of 100 S.aureus were isolates collected from various clinical specimens (skin and soft tissue infections, sputum and tracheobronchial fluids, blood, pharynx and urine) and sensitivity was determined to various commonly used antibiotics and vancomycin by disc diffusion method [Table:1]. The oxacillin salt agar (6 g/mL of oxacillin in Mueller Hinton agar with 4% NaCl) screening plate procedure was used for the detection of Oxacillin resistant S.aureus (ORSA) and then linezolid was tested against ORSA and Oxacillin sensitive S.aureus (OSSA) by both disc diffusion and agar dilution method in the concentration ranging from 0.12 to 16 mg/L. The recommendations of NCCLS were followed.[3]

Out of 100 S.aureus, 28 (28.0%) were ORSA and 80 (80%) were multiply resistant to more than 3 antimicrobials. Sensitivity of ORSA to tetracycline, erythromycin, cefazolin, amikacin and cefuroxime was quite low while 57.1% and 100% strains were sensitive to clindamycin and vancomycin respectively. By disc diffusion method 99% were linezolid sensitive. The MIC range for ORSA was 0.5-4mg/L with MIC50 2mg/L and MIC90 2mg/L. The MIC range for OSSA was 1-2 mg/L with MIC50 2mg/L and MIC90 2mg/L. The single isolate resistant by disc diffusion was ORSA with MIC 4 mg/L. Overall sensitivity of S.aureus to Linezolid was 100% by agar dilution method.

Linezolid is rapidly and completely absorbed after oral administration with a mean bioavailability of approximately 100%. Linezolid is indicated for adults in the treatment of nosocomial (i.e. hospital acquired) pneumonia, community acquired pneumonia, complicated and uncomplicated skin and skin structure infections and vancomycin resistant Enterococcus (VRE) infections. Other indications are gram positive complicated UTI, febrile neutropenia, osteomyelitis, endocarditis, and surgical prophylaxis in major surgery.[2] The oxazolidinones have a unique mechanism of action and do not exhibit cross resistance with existing agents.[4] Linezolid has good activity against staphylococci, including strains resistant to methicillin, glycopeptides and other antibacterial agents. It is also active against ciprofloxacin susceptible and resistant strains of multidrug resistant S.aureus.[2]

Our study shows that the activity of linezolid against a variety of multiply resistant S.aureus isolates is excellent. Also MIC study indicates that 100% S.aureus isolates (ORSA and OSSA) are linezolid susceptible. Our results are consistent with those reported by other groups.[1],[5] Thus linezolid is a promising therapeutic option in an era of rapidly growing antibiotic resistance.


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3National Committee for Clinical Laboratory standards. Methods for Dilution Antimicrobial Susceptibility tests for Bacteria that grow aerobically. 7th ed. Approved Standard, M7-A2. NCCLS, Villanova, PA, 2000.
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