Aims and objectives: Pseudomonas aeruginosa [PA] and Acinetobacter baumannii [AB] are important nosocomial pathogens in health care settings. Treatment is complicated by multi-drug resistance [MDR]. Increasing resistance to carbapenems mediated by metallobetalactamase [MBL] and other mechanisms is a cause for concern because they adversely affect clinical outcomes and add to treatment costs. This study was undertaken to determine the prevalence of MBL production in carbapenem-resistant isolates and to study the factors influencing the clinical outcomes of infections.
Methods: Fifty-five carbapenem-resistant nosocomial isolates of PA (30) and AB (25) were included for the study. Multidrug resistance was defined as being resistant to all classes of antibiotics including carbapenems. This was determined by disc diffusion method in accordance with CLSI. Minimum inhibitory concentration [MIC] to imipenem and meropenem was done by agar dilution method. MBL production was detected using ethylene diamine tetraacetic acid [EDTA] as inhibitor both by disc diffusion and MIC testing. Risk factors related to hospital and ICU stay were analysed. Outcomes were followed up. Proportions were compared using Chi square test to determine the factors influencing the outcome. Differences were considered significant if P was < 0.05.
Results: All isolates exhibited moderate to high degree of resistance to carbapenems. Their MIC ranged from 8-2048 mcg/ml. Crossresistance to cephalosporins, fluoroquinolones, aminoglycosides and beta lactam-betalactamase combination was seen in all isolates. Ninety two percent were susceptible to polymyxins. MBL was detected in 44 isolates [PA-29, AB-15], while 11 isolates were negative. The common site of isolation was the respiratory tract (41.8%) followed by urinary tract (25.5%), wound (20%) and blood (12.7%). Colonisation from infection was deliniated based on clinical and laboratory criteria. Death occured in 57% of patients. Factors contributing to mortality were length of hospital and ICU stay (P = 0.001), intubation (P = 0.0005), usage of multiple invasive devices and presence of a focal or a generalized infection (P = 0.001). Administration of multiple antibiotics did not affect the mortality
Conclusions: MBL-mediated carbapenem resistance in PA and AB is a significant threat in hospitalised patients. It should be addressed with infection control measures, surveillance and alternative new therapeutic strategies.