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JAC Advance Access published online on November 12, 2003
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkg486
© 2003 by The British Society for Antimicrobial Chemotherapy
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© 2003 The British Society for Antimicrobial Chemotherapy

Original article

Outer membrane protein alterations and blaTEM-1 variants: their role in {beta}-lactam resistance in Klebsiella pneumoniae

E. C. Nelson 1 , Heidi Segal 1 , and B. Gay Elisha 2 *

1 Department of Medical Microbiology, University of Cape Town, Cape Town;
2 Department of Medical Microbiology, University of Cape Town, Cape Town; National Health Laboratory Service, Cape Town, South Africa

* Corresponding author. E-mail: gelisha{at}curie.uct.ac.za.

Received 28 August 2003 ; revised 24 September 2003 ; accepted 27 September 2003

Abstract

Objectives: The aim of the study was to characterize the genetic basis of resistance to selected {beta}-lactam antibiotics in two clinical isolates of Klebsiella pneumoniae.

Methods and results: K. pneumoniae strains were isolated from two hospitalized patients. One of the strains was resistant to amoxicillin, co-amoxiclav, cefuroxime, piperacillin and cefoxitin but susceptible to all the other cephalosporins tested. The second strain displayed a similar phenotype except that it was resistant to piperacillin/tazobactam and susceptible to cefoxitin. PCR assays and DNA sequencing showed that the cefoxitin-susceptible strain contained a novel blaTEM-1 variant downstream of the strong Pa/Pb promoter. SDS-PAGE analysis of the outer membrane proteins (OMPs) did not identify OmpK35 and suggested reduced expression of OmpK36 in this strain. Following passage in non-selective media, expression of OmpK36 was restored with a concomitant increase in cefuroxime susceptibility. A similar experimental approach identified blaTEM-1C in the cefoxitin-resistant K. pneumoniae strain. This strain was deficient in OmpK35 and OmpK36; absence of the latter protein was due to the presence of IS1 in the ompK36 regulatory region.

Conclusions: Resistance to selected {beta}-lactams in two clinical isolates of K. pneumoniae was due to interplay between the expression of OMPs and TEM-1.

Keywords: cefuroxime, {beta}-lactamase, IS1, Pa/Pb
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