OmpK36 and TraN facilitate conjugal transfer of the Klebsiella pneumoniae carbapenem resistance plasmid pKpQIL

We investigated the mechanism of conjugal transfer of the endemic Klebsiella pneumoniae carbapenem resistance plasmid, pKpQIL. Transfer efficiency of this plasmid was found to be dependent on the expression of the major outer membrane porin, OmpK36, in recipient cells. We also found that conjugal uptake is reduced in recipients expressing an OmpK36 isoform associated with the globally pervasive K. pneumoniae ST258 clade (OmpK36ST258). This reduction was attributed to a glycine-aspartate insertion in loop 3 of OmpK36ST258, which constricts the pore by 26%. Deletion of finO, which encodes an RNA-binding protein, de-repressed transfer of pKpQIL and enabled visualisation of the conjugation pilus and OmpK36-dependent conjugation in real time. While deletion of traN abolished pKpQIL conjugation, substituting traN in pKpQIL with its homologue from R100-1 circumvented OmpK36 dependency. These results suggest that OmpK36 in recipient K. pneumoniae and the pKpQIL-encoded TraN in donor bacteria cooperate to facilitate plasmid transfer. This is the first report since 1998 to suggest a novel recipient cell receptor for IncF plasmid transfer and supports the idea that TraN mediates receptor specificity for plasmids belonging to this incompatibility group.