title: The Role of OmpK35, OmpK36 Porins, and Production of β-Lactamases on Imipenem Susceptibility in Klebsiella pneumoniae Clinical Isolates, Cairo, Egypt.
abstract: BACKGROUND
  OmpK35 and OmpK36 are the major outer membrane porins of Klebsiella pneumoniae. We aimed to study the effect of combined porin loss and production of extended-spectrum β-lactamases (ESBLs) on imipenem susceptibility among K. pneumoniae clinical isolates.
  
  
  METHODS
  This study included 91 suspected ESBL-producing K. pneumoniae clinical isolates, isolated from different patient specimens at the Cairo University hospital from January to June 2010. All isolates were subjected to genotypic analysis of the outer membrane protein gene expression using reverse transcription-PCR (RT-PCR) and analysis of OmpK35/36 of 38 isolates by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).
  
  
  RESULTS
  By RT-PCR, loss of Omp35 was detected in 78 (85.7%) isolates, loss of Omp36 was detected in 64 (70.32%), and loss of both porins was detected in 62 (68.1%). Out of 91 isolates, 45 (49.5%) were resistant to cefoxitin, and 17 (18.7%) were confirmed as derepressed AmpC producers. Omp35 was lost in all FOX-resistant isolates, whereas Omp36 was lost in 42 (93.3%) (p-value 0.002). The mean of ceftazidime inhibition zone diameter was significantly decreased among ESBL-producing isolates with loss of Omp35/36 (p-value 0.041 and 0.006), respectively. The mean of imipenem minimal inhibitory concentration (MIC) was markedly increased to 8.55 μg/ml among AmpC-producing isolates with Omp35/36 loss, while the mean of imipenem MIC among the 66 confirmed ESBL producers was 0.32 μg/ml.
  
  
  CONCLUSIONS
  Imipenem MIC was markedly increased among K. pneumoniae isolates showing AmpC production with loss of both porins OmpK35/36. Meanwhile, the association of porin OmpK35/36 loss with ESBL production was not a direct cause of resistance to imipenem.
authors.affiliation: Department of Clinical and Chemical Pathology, Faculty of Medicine, Cairo University , Cairo, Egypt .
authors.forename: Mona
authors.initials: M
authors.lastname: Wassef
authors.affiliation: Department of Clinical and Chemical Pathology, Faculty of Medicine, Cairo University , Cairo, Egypt .
authors.forename: Mona
authors.initials: M
authors.lastname: Abdelhaleim
authors.affiliation: Department of Clinical and Chemical Pathology, Faculty of Medicine, Cairo University , Cairo, Egypt .
authors.forename: Eiman
authors.initials: E
authors.lastname: AbdulRahman
authors.affiliation: Department of Clinical and Chemical Pathology, Faculty of Medicine, Cairo University , Cairo, Egypt .
authors.forename: Doaa
authors.initials: D
authors.lastname: Ghaith
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002440:Cefoxitin / Q000494:pharmacology; D004534:Egypt / Q000453:epidemiology; D015964:Gene Expression Regulation, Bacterial; D006785:Hospitals, University; D006801:Humans; D015378:Imipenem / Q000494:pharmacology; D007710:Klebsiella Infections / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology; D007711:Klebsiella pneumoniae / Q000187:drug effects / Q000201:enzymology / Q000235:genetics* / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D018272:Porins / Q000172:deficiency / Q000235:genetics*; D018440:beta-Lactam Resistance / Q000235:genetics*; D001618:beta-Lactamases / Q000235:genetics* / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; C119261:OmpK35 porin, Klebsiella pneumoniae; C092233:OmpK36 protein, Klebsiella pneumoniae; D018272:Porins; D002440:Cefoxitin; D015378:Imipenem; C048795:AmpC beta-lactamases; D001618:beta-Lactamases