Antimicrobial susceptibility against metronidazole and carbapenem in clinical anaerobic isolates from Pakistan

Globally metronidazole and carbapenem resistance in anaerobic organisms is increasing necessitating continuous surveillance to guide selection of empirical treatment. In this study we have determined metronidazole resistance in anaerobes using MIC Evaluator strips (M.I.C.E strips). Carbapenem resistance was evaluated only in metronidazole resistant isolates. The study was conducted at the Aga Khan University (AKU) Hospital laboratory, Karachi, Pakistan (2014-2017). Metronidazole and imipenem resistance was evaluated using M.I.C.E strips and minimum inhibitory concentrations (MICs) were interpreted using Clinical Laboratory Standards Institute (CLSI) criteria. Clinical details including demographics, prolonged hospital stay, malignancy, transplant, dialysis, diabetes, site of infection and outcome were analyzed for association with metronidazole resistance. Of the 223 clinically significant isolates, 39 (17.5%) were metronidazole resistant (excluding the inherently resistant organisms; for example species). Imipenem resistance was determined in 29 metronidazole resistant isolates and of these 7 (24.1%) were found to be resistant. Proportion of metronidazole resistant strains was highest amongst species. A significant increase in metronidazole resistance from 12.3% in 2010-2011 to 17.5% in the current study was found. Carbapenem resistance also emerged in the period 2014-2017.Isolates from malignancy and transplant patients showed lower odds of developing metronidazole resistance (0.003(95% CI: 1.7-17.9)). Prolonged hospital stay was not associated with metronidazole resistance (1.1((95% CI: 0.5-2.5)). The rising trend of metronidazole resistance and emergence of carbapenem resistance in anaerobic bacteria is alarming. Continued surveillance with strengthening of laboratory capacity regarding anaerobic susceptibility testing is urgently needed in Pakistan.