Acquisition of carbapenem resistance in multiresistant Klebsiella pneumoniae strains harbouring blaCTX-M-15, qnrS1 and aac(6')-Ib-cr genes.

Three closely related Klebsiella pneumoniae strains isolated from the same patient harboured bla(CTX-M-15), bla(OXA-1), bla(SHV-11), qnrS1, aac(6')-Ib-cr, oqxAB, aac(3)-II and aph(3')-Ia genes. Two of the isolates were recovered after treatment with meropenem and showed resistance to carbapenems. Sequencing of ompK35 and ompK36 porin genes of the carbapenem-resistant strains revealed the presence of premature stop codons in both, and OmpK35 and OmpK36 porins were not detected by SDS-PAGE. One carbepenem-resistant strain showed a high amount of LamB protein and did not express OmpK26 porin whereas the other strain expressed OmpK26 but not LamB. The lack of major porins apparently causes changes in the expression of other, specific, porins.