Outbreak of extended-spectrum beta-lactamase VEB-1-producing isolates of Acinetobacter baumannii in a French hospital

Abstract

Twelve clonally related and multidrug-resistant Acinetobacter baumannii isolates were recovered during a 4-month period from 12 patients hospitalized at the Valenciennes Hospital in France. Antibiograms determined by the double-disk diffusion technique on cloxacillin-containing plates detected a clavulanic acid-inhibited extended-spectrum beta-lactamase (ESBL). PCR and sequencing identified the gene encoding the Ambler class A ESBL VEB-1. This gene was located on the chromosome and was part of a class 1 integron identical to that previously identified in Pseudomonas aeruginosa isolates from Thailand. Additionally, seven clonally related bla(VEB-1)-positive A. baumannii strains were identified in the immediate environment of the hospitalized patients. This is the first report of the ESBL VEB-1 in Acinetobacter spp. and the first description of VEB-1-producing strains as a source of an outbreak occurring outside Southeast Asia. This report underlines the difficulty of the identification of ESBLs in A. baumannii.

FIG. 1.

Double-disk synergy test with bla_VEB-1-positive A. baumannii strain AYE. MH agar plates contained either no cloxacillin (A) or 200 μg of cloxacillin per ml (B). The disks tested contained ceftazidime (CAZ), cefuroxime (CXM), ticarcillin-clavulanic acid (TCC), cefoxitin (FOX), and cefepime (FEP).

FIG. 2.

Schematic representation of the veb-1 gene cassette-containing integron found in A. baumannii AYE. Gene cassettes are shown as boxes, with arrows indicating the orientation of transcription and black circles indicating the 59-base element. The 5′ conserved segment contains the intI1 gene, which encodes integrase; and the 3′ conserved segment, downstream of the gene cassettes, includes the qacEΔ1 gene, an antiseptic resistance determinant. The IS1999 inverted repeats are indicated by filled and empty triangles.

FIG. 3.

(A) PFGE profiles of I-CeuI-digested whole-cell DNA of three A. baumannii strains. Lanes 1, A. baumannii AYE (bla_VEB-1 positive); lanes 2, A. baumannii isolate 13 (bla_VEB-1 negative); lanes 3, A. baumannii reference strain CIP7034^T (bla_VEB-1 negative); lane M, bacteriophage lambda DNA ladder. Southern hybridization was done with a 16S-23S rRNA gene-specific probe (B) and a bla_VEB-1-specific internal probe (C).

FIG. 4.

PFGE profiles of ApaI-digested whole-cell DNA of 21 A. baumannii isolates. Lane 0, A. baumannii reference strain CIP7034^T; lanes 1 to 20, A. baumannii isolates 1 to 20 (clinical isolates 1 to 13 and environmental isolates 14 to 20, respectively). Clinical isolate 3 is also referred as AYE throughout the text. Lane M, bacteriophage lambda DNA ladder.