JAC Advance Access originally published online on November 12, 2003
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Journal of Antimicrobial Chemotherapy (2003) 52, 899-903
© 2003 The British Society for Antimicrobial Chemotherapy
Outer membrane protein alterations and blaTEM-1 variants: their role in ß-lactam resistance in Klebsiella pneumoniae
1 Department of Medical Microbiology, University of Cape Town, Cape Town; 2 National Health Laboratory Service, Cape Town, South Africa
Received 28 August 2003; returned 15 September 2003; revised 24 September 2003; accepted 27 September 2003
Objectives: The aim of the study was to characterize the genetic basis of resistance to selected ß-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 ß-lactams in two clinical isolates of K. pneumoniae was due to interplay between the expression of OMPs and TEM-1.
Keywords: cefuroxime, ß-lactamase, IS1, Pa/Pb
* Correspondence address. Department of Medical Microbiology, Medical School, University of Cape Town, Anzio Road, Observatory 7925, Cape Town, South Africa. Tel: +27-21-4066378; Fax: +27-21-4488153; E-mail: gelisha{at}curie.uct.ac.za
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