Current status of Glycopeptide intermediate and heterogenous Glycopeptide intermediate Staphylococcus aureus and their prevailing susceptibility pattern at two tertiary care hospitals of Pakistan

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Background: Glycopeptides have been used widely to treat methicillin resistant Staphylococcus aureus (MRSA) infections. Until recently vancomycin resistance among gram-positive bacteria had been thought to be uncommon but Glycopeptide intermediate S. aureus (GISA) and heterogenous GISA (hGISA) have been reported from various parts of world. Strains of hGISA have MICs considered to be in the susceptible range (≤2.0 μg/ml) but contain a subset of the bacterial population that expresses the resistance phenotype.This study has been done to evaluate the current status of glycopeptides intermediate and heterogenoiously 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 ≥ 1μg/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.