The evolution of multidrug resistance in Klebsiella species in response to selective pressure and the extent to which this may be reversible is not fully understood. Since the spread of carbapenem-resistant Enterobacteriaceae (CRE) is considered a public health threat by the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC), more studies are needed to understand the evolution of antibiotic resistance mechanisms to determine if it is possible to reverse this trend.
A clinical Klebsiella quasipneumoniae isolate called FK688, which caused a bloodstream infection in a hospital patient, is resistant to multiple antibiotics, including third-generation cephalosporins and carbapenems. Analysis of the complete FK688 genome, machine learning and enzymatic analysis revealed no carbapenemase-encoding genes and that epistatic changes are necessary for FK688 to reflect a CRE phenotype.
Evolution experiments demonstrated the fitness burden associated with the antimicrobial resistance determinants and the reversion to a carbapenem susceptible phenotype in an antibiotic-free environment. Fitness assays showed that a low concentration of ceftazidime selects for a β-lactamase gene and can potentiate evolution to carbapenem resistance by a single-step mutation in the porin OmpK36. The experiments in this study demonstrated the importance of epistatic events and how variation in drug exposure can shape the evolutionary pathway to antibiotic resistance.