# Molecular mechanisms of disinfectant resistance in Klebsiella pneumoniae

## TL;DR

This study explores how Klebsiella pneumoniae develops resistance to common disinfectants, revealing molecular mechanisms that could help improve infection control strategies.

## Contribution

The study identifies specific molecular adaptations in Klebsiella pneumoniae that confer resistance to multiple disinfectants, including cross-resistance mechanisms.

## Key findings

- Adaptation to BAC, DDAC, and PHMB involves lipid A modification, reducing the bacterial surface's negative charge and disinfectant affinity.
- Chlorocresol resistance is linked to increased efflux pump activity and biofilm formation.
- Bronopol resistance involves biofilm promotion and thioredoxin upregulation, with NemA potentially degrading bronopol.

## Abstract

Chemical disinfectants are critical for infection control in healthcare environments and beyond, as exemplified by their vital role during the COVID-19 pandemic. Despite research repeatedly demonstrating that bacteria can develop adaptations that mitigate the efficacy of chemical disinfectants, the underlying molecular mechanisms remain poorly characterized. This study investigates the mechanisms that underpin resistance demonstrated by disinfectant-adapted Klebsiella pneumoniae NCTC 13443 samples.

Resistant samples have previously undergone long-term in vitro adaptation via serial passage in increasing concentrations of common disinfectants benzalkonium chloride (BAC), didecydimethylammonium chloride (DDAC), polyhexamethylene biguanide (PHMB), chlorocresol or bronopol. A multi-omics approach was used to conduct in-depth molecular analyses of the adaptations that contribute to resistance.

K. pneumoniae adaptation to BAC, DDAC and PHMB was associated with the modification of lipid A causing the reduction of the net-negative charge of the outer surface, lowering the affinity of cationic disinfectants. This mechanism is also used for polymyxin and colistin resistance, highlighting a potential cross-resistance risk. Chlorocresol-adapted K. pneumoniae samples demonstrated increased expression of efflux pumps and expression changes linked to biofilm formation. Bronopol resistance was associated with promoting biofilm formation and increased thioredoxin expression to alleviate oxidative stress. Results indicate the potential role of N-ethylmaleimide reductase NemA in bronopol resistance via enzymatic degradation.

These findings provide novel insights into how causative pathogens of healthcare-associated infections can adapt to and mitigate the effectiveness of common chemical disinfectants that are relied on globally every day as a critical infection control measure.