In vivo selection of porin-deficient mutants of Klebsiella pneumoniae with increased resistance to cefoxitin and expanded-spectrum-cephalosporins

Abstract

Four Klebsiella pneumoniae isolates (LB1, LB2, LB3, and LB4) with increased antimicrobial resistance were obtained from the same patient. The four isolates were indistinguishable in biotype, plasmid content, lipopolysaccharide, and DNA analysis by pulse-field gel electrophoresis. Isolate LB1 made TEM-1 and SHV-1 beta-lactamases. Isolates LB2, LB3, and LB4 produced SHV-5 in addition to TEM-1 and SHV-1. MICs of cefoxitin, ceftazidime, and cefotaxime against LB1 were 4, 1, and 0.06 micrograms/ml, respectively. MICs of ceftazidime against K. pneumoniae LB2, LB3, and LB4 were > 256 micrograms/ml, and those of cefotaxime were 2, 4, and 64 micrograms/ml, respectively. MICs of cefoxitin against K. pneumoniae LB2 and LB3 were 4 micrograms/ml, but that against K. pneumoniae LB4 was 128 micrgrams/ml. K. pneumoniae LB4 could transfer resistance to ceftazidime and cefotaxime, but not that to cefoxitin, to Escherichia coli. Isolate LB4 and cefoxitin-resistant laboratory mutants lacked an outer membrane protein of about 35 kDa whose molecular mass, mode of isolation, resistance to proteases, and reaction with a porin-specific antiserum suggested that it was a porin. MICs of cefoxitin and cefotaxime reverted to 4 and 2 micrograms/ml, respectively, when isolate LB4 was transformed with a gene coding for the K. pneumoniae porin OmpK36. We conclude that the increased resistance to cefoxitin and expanded-spectrum cephalosporins of isolate LB4 was due to loss of a porin channel for antibiotic uptake.

Linkage of ciprofloxacin resistance with a single genotypic cluster of Klebsiella pneumoniae

“…The same finding has been suggested in another study [14]. However, the exact nature of the protein has not been established, and the assumption that the involved proteins were porins was largely based on their molecular masses [15].…”

Occurrence of plasmidic AmpC type β-lactamase-mediated resistance in Escherichia coli: report from the SENTRY Antimicrobial Surveillance Program (North America, 2004)

“…Five E. coli isolates showing a positive 3D AmpC test and a negative ESBL confirmatory test failed to generate PCR products. These isolates may produce enzymes not covered by the selected PCR primer sets or may have additional mutations affecting porin channels for antimicrobial uptake [13]. The three remaining strains had a negative 3D AmpC test and only an isolated elevation of the ceftazidime MIC (2 mg/L), the latter indicating a lack of specificity at this ESBL screening concentration [5].…”

Risk Factors of Nosocomial Infection with Extended-Spectrum Beta-Lactamase-Producing Bacteria in a Neonatal Intensive Care Unit in China

“…This is in consistence with reports that some clinical isolates of ESBL-producing K. pneumoniae were found to be less susceptible to beta-lactam-beta-lactamase inhibitor combinations because of hyperproduction of ESBLs [37,38]. In addition, ESBL-producing K. pneumoniae can develop resistance to cefoxitin and expanded-spectrum-cephalosporins in vitro or in vivo by loss or decreased expression of porin channels for beta-lactamase inhibitor entry into the bacteria, indicating that other factors may interfere with susceptibility of bacteria to beta-lactamase inhibitor in addition to production of ESBLs [39]. Therefore, the role of beta-lactamase inhibitor therapy in severe neonatal nosocomial infection warrants further investigations.…”