Abstract
In Gram-negative bacteria, the permeability of the outer membrane governs rates of antibiotic uptake and thus the efficacy of antimicrobial treatment. Hydrophilic drugs like β-lactam antibiotics depend on diffusion through pore-forming outer membrane proteins to reach their intracellular targets. In this study, we investigated the distribution of porin genes in more than 2,700 Klebsiella isolates and found a widespread loss of OmpK35 functionality, particularly in those strains isolated from clinical environments. Using a defined set of outer-membrane-remodeled mutants, the major porin OmpK35 was shown to be largely responsible for β-lactam permeation. Sequence similarity network analysis characterized the porin protein subfamilies and led to discovery of a new porin family member, OmpK38. Structure-based comparisons of OmpK35, OmpK36, OmpK37, OmpK38, and PhoE showed near-identical pore frameworks but defining differences in the sequence characteristics of the extracellular loops. Antibiotic sensitivity profiles of isogenic Klebsiella pneumoniae strains, each expressing a different porin as its dominant pore, revealed striking differences in the antibiotic permeability characteristics of each channel in a physiological context. Since K. pneumoniae is a nosocomial pathogen with high rates of antimicrobial resistance and concurrent mortality, these experiments elucidate the role of porins in conferring specific drug-resistant phenotypes in a global context, informing future research to combat antimicrobial resistance in K. pneumoniaeIMPORTANCEKlebsiella pneumoniae is a pathogen of humans with high rates of mortality and a recognized global rise in incidence of carbapenem-resistant K. pneumoniae (CRKP). The outer membrane of K. pneumoniae forms a permeability barrier that modulates the ability of antibiotics to reach their intracellular target. OmpK35, OmpK36, OmpK37, OmpK38, PhoE, and OmpK26 are porins in the outer membrane of K. pneumoniae, demonstrated here to have a causative relationship to drug resistance phenotypes in a physiological context. The data highlight that currently trialed combination treatments with a carbapenem and β-lactamase inhibitors could be effective on porin-deficient K. pneumoniae Together with structural data, the results reveal the role of outer membrane proteome remodeling in antimicrobial resistance of K. pneumoniae and point to the role of extracellular loops, not channel parameters, in drug permeation. This significant finding warrants care in the development of phage therapies for K. pneumoniae infections, given the way porin expression will be modulated to confer phage-resistant-and collateral drug-resistant-phenotypes in K. pneumoniae.