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


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.
Nelson
E C
EC
Department of Medical Microbiology, University of Cape Town, Cape Town, South Africa.
Segal
Heidi
H
Elisha
B Gay
BG
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial; D004591:Electrophoresis, Polyacrylamide Gel; D005798:Genes, Bacterial / Q000235:genetics; D006801:Humans; D007710:Klebsiella Infections / Q000382:microbiology; D007711:Klebsiella pneumoniae / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics; D008826:Microbial Sensitivity Tests; D010641:Phenotype; D018272:Porins / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D001618:beta-Lactamases / Q000235:genetics*; D047090:beta-Lactams / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D004269:DNA, Bacterial; D018272:Porins; D047090:beta-Lactams; D001618:beta-Lactamases; C034413:beta-lactamase TEM-1