Resistance to extended-spectrum β-lactams by the emergence of SHV-12 and the loss of OmpK35 in Klebsiella pneumoniae and Escherichia coli in Malaysia
Selvi Palasubramaniam, Sekaran Muniandy, Parasakthi Navaratnam
Department of Medical Microbiology and Department of Molecular Medicine, University of Malaya, Kuala Lumpur; and School of Medicine and Health Sciences, Monash University Malaysia, Petaling Jaya, Malaysia
Received: June 18, 2007 Revised: August 2, 2007 Accepted: November 3, 2007
Background and purpose:
In addition to β-lactamase production, loss of porins confers resistance to extended-spectrum β-lactams in Klebsiella pneumoniae and Escherichia coli infection. This study describes the detection of SHV-12 extended-spectrum β-lactamase (ESBL) subtype and the loss of OmpK35 porin in 4 strains of K. pneumoniae and E. coli.
Isoelectric focusing was performed to detect β-lactamases in 4 strains of K. pneumoniae and E. coli. The presence of the SHV gene in the 4 isolates was characterized by polymerase chain reaction, DNA sequencing, and DNA hybridization. Loss of porin in these strains was analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blot analysis.
The strains of K. pneumoniae and E. coli were confirmed to be ESBL producers and were resistant to cefoxitin, with minimal inhibitory concentration values of 512 μg/mL. All 4 strains had β-lactamases with an isoelectric value of 8.2. The SHV gene from these strains was characterized to be the SHV-12 subtype and was plasmid-borne. The deduced amino acid sequence showed that the SHV-12 β-lactamase was a derivative of the more common ESBL, SHV-5 subtype. All the strains showed absence of the OmpK35 porin.
Resistance of the strains towards extended-spectrum β-lactams was a result of a dualmechanism — the production of SHV-12 enzymes and loss of the OmpK35 porin.
beta-Lactamase SHV-12; Escherichia coli; Klebsiella pneumoniae; OmpK35 porin, Klebsiella pneumoniae
J Microbiol Immunol Infect. 2009;42:129-133.