In vitro antimicrobial activity of colistin in combination with rifampicin against carbapenem-resistant Acinetobacter baumannii

Abstract

intermediate strains of MRSA. Suscpetibility pattern has also been studied to formulate an effective, inexpensive and easily administered empirical therapy for GISA and hGISA. Methods: Three hundred and Forty seven MRSA isolated from the clinical specimens of Allied hospitals of AMC/NUST and PAEC General Hospital, Pakistan were subjected to the determination of Vancomycin minimum inhibitory concentration (MIC) and isolates having vancomycin MIC ≥ 1g/ml were subjected to determination of Glycopeptide resistance detection (GRD) using Etest. Susceptibility pattern of all the isolates were recorded using Kirby baur disc diffusion method and MIC for linezolid, daptomycin, chloramphenicol, minocycline and tigecycline using E-strips. MIC 50 and MIC 90 were calculated Results: All isolates were sensitive to vancomycin but 197 isolates showed higher MICs and 6 turned out to be heterogenous Glycopeptide intermediate (h GISA) strains. All the isolated organisms were highly susceptible to linezolid (98.3%), daptomycin (100%), chloramphenicol (96%), minocycline (95.7%) and tigecycline (94.8%). Conclusion: Significant number of isolates having MIC of vancomycin equal to or more than 1 ug/ml have been isolated and these can turn out to be GISA/h GISA. Vancomycin Susceptibility breakpoints as indicated by CLSI should be reevaluated because that doesn't cover GISA/h GISA isolates. This study suggests that linezolid, chloramphenicol, minocycline, daptomycin and tigecycline have high in vitro efficacy for MRSA infections. Prescribing antibiotics other than glycopeptides for MRSA infections will minimize the chances of emergence of GISA. Good hospital infection control measures prove to be the main stay against these infections because antibiotics can never be an effective alternative to good medical practice.