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Journal of Clinical Microbiology, September 2000, p. 3299-3305, Vol. 38, No. 9
Servicio de Microbiología, Hospital
Ramón y Cajal, 28034 Madrid,1 and
Servicio de Microbiología, Hospital de Bellvitge,
CSUB, Barcelona,2 Spain
Received 1 February 2000/Returned for modification 3 April
2000/Accepted 22 June 2000
From February to November 1997, 29 inpatients at Ramón y
Cajal Hospital, Madrid, Spain, were determined to be either colonized or infected with imipenem- and meropenem-resistant Acinetobacter baumannii (IMRAB) strains (MICs, 128 to 256 µg/ml). A wide
antibiotic multiresistance profile was observed with IMRAB strains. For
typing IMRAB isolates, pulsed-field gel electrophoresis was used. For comparative purposes, 30 imipenem- and meropenem-susceptible A. baumannii (IMSAB) strains isolated before, during, and after the outbreak were included in this study. The molecular-typing results showed that the outbreak was caused by a single IMRAB strain (genotype A). By cloning experiments we identified a class D
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Copyright © 2000, American Society for Microbiology. All rights reserved.
Characterization of a Nosocomial Outbreak Caused by a
Multiresistant Acinetobacter baumannii Strain with a
Carbapenem-Hydrolyzing Enzyme: High-Level Carbapenem Resistance in
A. baumannii Is Not Due Solely to the Presence of
-Lactamases
-lactamase (OXA-24) encoded in the chromosomal DNA of this IMRAB strain which showed carbapenem hydrolysis. Moreover, the outer membrane profile of
the IMRAB strain showed a reduction in the expression of two porins at
22 and 33 kDa when compared with genetically related IMSAB isolates. In
addition no efflux mechanisms were identified in the IMRAB strains. In
summary, we report here the molecular characterization of a nosocomial
outbreak caused by one multiresistant A. baumannii epidemic
strain that harbors a carbapenem-hydrolyzing enzyme. Although
alterations in the penicillin-binding proteins cannot be ruled out, the
reduction in the expression of two porins and the presence of this
OXA-derived
-lactamase are involved in the carbapenem resistance of
the epidemic nosocomial IMRAB strain.
*
Corresponding author. Present address: Laboratory of
Viral Immunology, Department of Immunology and Division of Infectious Diseases, 200 First St., Guggenheim 516 SW, Mayo Clinic, Rochester, MN
55905. Phone: (507) 284-9646. Fax: (507) 284-3757. E-mail: germanbou{at}mailcity.com.
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