Bad Bugs and No Drugs: Activity of Colistin as Waging War against Emerging Metallo-β-Lactamases Producing Pathogens

Inter-hospital and intra-hospital dissemination of metallo-β-lactamase (MβL) producing strains possess significant therapeutic challenges. Objective: This study was carried out to evaluate the efficacy of Colistin against MβL producers. Material and Methods: This cross-sectional study was conducted in Microbiology Laboratory, Allama Iqbal Medical College, Lahore, Pakistan from 1stJuly 2016 to 25th February 2017. A total of 12126 clinical samples were collected from patients presenting to Jinnah Hospital, Lahore. Every sample was processed for bacterial culture. Bacterial identification was performed according to standard guidelines. Every gram-negative isolate was further processed for antimicrobial susceptibility testing by modified Kirby Baur disc diffusion method. Zone sizes were interpreted according to CLSI 2016 guidelines. Next day every carbapenem-resistant isolate were further processed for MβL detection by EDTA method, zone size of Carbapenem disc only and Carbapenem disc impregnated with EDTA was compared ( >7 mm increase MβL positive, 0-5 mm increase MβL-negative). Results: Out of total 12126 samples, 35.9% (n=4361) were culture positive and only 40.5% (n=1770) were Gram negative rods. Of these 9.6% (n=170) were Carbapenem-resistant isolates with 47% (n=80) MβL producers. Briefly 51.7% (n=30) Acinetobacter species were MβL positive, Pseudomonas species 38.5% (n=22), Escherichia coli 69.5% (n=16), Klebsiella species 37.0% (n=10), Proteus 66.6% (n=2) and 0% Citrobacter sppwere MβL positive. 32.5% MβL positive isolates were from ICU, 21.2% were from OPD, 12.5%were from Surgical Units, 12.5% were from Medical Unit, 17.5% were from Orthopedic Unit, and 3.7% were from Pulmonology ward. Almost 100% resistant was observed in MβL positive isolates for Imipenem,Piperacillin+ Tazobactum, Ceftriaxone, Co-amoxyclav, Cefoperazone+Sulbactam, Ciprofloxacin, and Amikacin, Doxycycline, and Gentamicin showed 91.2%, 94.0%, and 97.5% resistant rate respectively. No resistance was observed against Colistin. Conclusion: MβL producing Gram negative rods are rising in clinical setups. They are becoming a nightmare for clinicians to treat such infections. Colistin remains the only choice of drug for MβL positive and Negative isolates with 0% resistant rate except for Proteus species, to which it is intrinsically resistant.