Successive emergence of extended-spectrum beta-lactamase-producing and carbapenemase-producing Enterobacter aerogenes isolates in a university hospital.
Sixty-two clinical isolates of Enterobacter aerogenes resistant to expanded-spectrum cephalosporins were collected between July 2003 and May 2005. Among these isolates, 23 (37.1%) were imipenem (IPM) susceptible, and 39 (62.9%) were IPM insusceptible, of which 89.7% (35/39) were resistant and 10.3% (4/39) were intermediate. Isolate genotypes were compared by pulsed-field gel electrophoresis. Of 62 isolates, 48 belonged to epidemic pulsotype A (77.4%). This pulsotype included 37.5% and 58.4% of beta-lactam phenotypes b and a, respectively. Nine isolates (14.5%) belonged to pulsotype E, which included 22.3% and 77.7% of phenotypes b and a, respectively. The beta-lactamases with pIs of 5.4, 6.5, 8.2, and 8.2 corresponded to extended-spectrum beta-lactamases (ESBLs) TEM-20, TEM-24, SHV-5, and SHV-12, respectively. Of 39 IPM-insusceptible E. aerogenes isolates, 26 (66.6%) were determined to be metallo-beta-lactamase producers, by using a phenotypic method. Of these isolates, 24 harbored a bla(IMP-1) gene encoding a protein with a pI of >9.5, and two carried the bla(VIM-2) gene encoding a protein with a pI of 5.3, corresponding to beta-lactamases IMP-1 and VIM-2, respectively. The remaining 13 (33.4%) isolates were negative for the bla(IMP-1) and bla(VIM-2) genes but showed an alteration of their outer membrane proteins (OMPs). Ten of these isolates produced the two possible OMPs (32 and 42 kDa), with IPM MICs between 8 and 32 microg/ml, and three others produced only a 32-kDa OMP with IPM MICs >32 microg/ml. This work demonstrates that, in addition to resistance to expanded-spectrum cephalosporins, IPM resistance can occur in ESBL-producing E. aerogenes isolates by carbapenemase production or by the loss of porin in the outer membrane.
Biendo
M
M
Laboratoire de Bactériologie-Hygiène, CHU Nord-Place Victor Pauchet-80054 Amiens, Cedex 1, France. Biendo.Maurice@chu-amiens.fr
Canarelli
B
B
Thomas
D
D
Rousseau
F
F
Hamdad
F
F
Adjide
C
C
Laurans
G
G
Eb
F
F
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D018550:Cephalosporin Resistance; D021902:Enterobacter aerogenes / Q000187:drug effects / Q000201:enzymology / Q000302:isolation & purification*; D004756:Enterobacteriaceae Infections / Q000453:epidemiology* / Q000382:microbiology; D005260:Female; D005602:France / Q000453:epidemiology; D006785:Hospitals, University; D006801:Humans; D007525:Isoelectric Focusing; D008297:Male; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D018272:Porins / Q000032:analysis; D017422:Sequence Analysis, DNA; D001618:beta-Lactamases / Q000096:biosynthesis* / Q000235:genetics
D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D018272:Porins; D001618:beta-Lactamases; C063912:carbapenemase