Adaptations of carbapenem resistant (CRAB) in the hospital environment causing sustained outbreak.

Carbapenem resistance in () is an emerging global threat. The adaptation strategies of for this emergence as a nosocomial pathogen has been less studied. This prospective study analysed a sustained outbreak of carbapenem resistant (CRAB) in the intensive care unit (ICU) with reference to antimicrobial resistance and virulence in the colonizing and pathogenic isolates under carbapenem stress. The CRAB isolates from initial and sustained outbreak were found harbouring multiple carbapenemase genes. These genes included , and . From NICU environment three phenotypically carbapenem susceptible isolates were found carrying , genes. Prior imipenem therapy was one of the risk factors (=0.0016). The outbreak was polyclonal. Under imipenem stress, outbreak isolates showed no loss of carbapenemase genes against stress free conditions (23.7±1.33 days). Biofilm formation increased with imipenem concentration, with outbreak isolates producing highest biomass. While the pathogens showed a slow growth rate on imipenem exposure, the colonisers grew rapidly ( <0.0001). Sustained outbreak of CRAB was identified in the ICU (July 2015 to December 2017). Risk factors for acquisition of CRAB was studied. isolates were also collected from the environments of ICU and neonatal ICU (NICU) and blood cultures of septic neonates. Isolates were characterized based on antimicrobial susceptibility, genetic profile, integrons carriage and clonality. Biofilm formation and growth kinetics were studied under varying carbapenem stress. Intense carbapenem exposure in the ICU facilitates persistence of CRAB by several adaptations causing sustained outbreaks.