Porins are bacterial outer membrane proteins which facilitate the diffusion of small hydrophilic molecules across the lipid membrane. In Klebsiella pneumoniae, two highly abundant major porins, OmpK35 and OmpK36, are responsible for general nutrient import, but have also been shown to allow the passage of various antibiotics, in particular β-lactams including carbapenems. Hence, as a mechanism to decrease antimicrobial influx, multidrug resistant clinical isolates often lack one or both major porins. To compensate for the simultaneous decrease in nutrient diffusion and waste efflux, alternative porins are commonly upregulated.
As the effectiveness of antimicrobial treatment is directly affected by the pore properties of the expressed porins, we investigate how major and alternative porins regulate antibiotic uptake. By expressing a set of porins (OmpK35, OmpK36, OmpK37, OmpK26, PhoE or LamB) in K. pneumoniae and measuring the minimal inhibitory concentration of various antibiotics, we are able to determine the individual diffusion properties of each channel. Together with structural information, these experiments elucidate the role of porins in drug-resistant phenotypes in K. pneumoniae.