CrrB Positively Regulates High-Level Polymyxin Resistance and Virulence in Klebsiella pneumoniae
Thomas H. McConville, Medini K. Annavajhala, Marla J. Giddins, Nenad Maćešić, Carmen M. Herrera, Felix D. Rozenberg, Gitanjali Bhushan, Danielle Ahn, Filippo Mancia, M. Stephen Trent, Anne‐Catrin Uhlemann
Abstract
Polymyxin resistance (PR) threatens the treatment of carbapenem-resistant Klebsiella pneumoniae (CRKP) infections. PR frequently arises through chemical modification of the lipid A portion of lipopolysaccharide. Various mutations are implicated in PR, including in three two-component systems-CrrA/B, PmrA/B, and PhoP/Q-and the negative regulator MgrB. Few have been functionally validated. Therefore, here we adapt a CRISPR-Cas9 system to CRKP to elucidate how mutations in clinical CRKP isolates induce PR. We demonstrate that CrrB is a positive regulator of PR, and common clinical mutations lead to the addition of both 4-amino-4-deoxy-L-arabinose (L-Ara4N) and phosophethanolamine (pEtN) to lipid A, inducing notably higher polymyxin minimum inhibitory concentrations than mgrB disruption. Additionally, crrB mutations cause a significant virulence increase at a fitness cost, partially from activation of the pentose phosphate pathway. Our data demonstrate the importance of CrrB in high-level PR and establish important differences across crrB alleles in balancing resistance with fitness and virulence.