The Development of Disinfectant Tolerance in Klebsiella pneumoniae.

Disinfectants are a critical infection control measure that are relied upon globally in a range of settings including healthcare, food production, and domestic environments. However, bacteria have been shown to survive disinfectant treatments when harboured in dry surface biofilms or when disinfectants are used ineffectively. This provides an opportunity for organisms to develop low-level tolerance to various disinfectants. The capability of bacteria to develop adaptations to non-antibiotic antimicrobial agents is often overlooked. This study investigates the ability of Klebsiella pneumoniae NDM-1 strain NCTC 13443 to adapt to a range of common chemical disinfectants (benzalkonium chloride, didecyldimethylammonium chloride, polyhexamethylene biguanide, chlorocresol and bronopol) via serial passage exposure method. After long-term adaptation K. pneumoniae developed tolerance to all tested disinfectants, exhibiting a minimum inhibitory concentration increase of between 30-413% compared to the untreated parent samples. Characterisation of disinfectant cross-tolerance showed that while cross-tolerance can occur, most adapted samples became more susceptible to the second disinfectant treatment, likely because of the fitness cost of adaptation. Observed cross-tolerance/increased susceptibility was not always reciprocated between disinfectant-tolerant samples, indicating that the order of disinfectant exposure is important during tolerance development. This has significant implications for disinfectant cleaning routines, and is likely due to variations in the underpinning tolerance mechanisms, even when the disinfectants display similar mechanisms of action. This study reports the capability and readiness of clinically relevant K. pneumoniae to adapt to common disinfectants that are relied upon every day across the world, delivering much-needed insights into an often-overlooked aspect of antimicrobial resistance.