blaVIM-2-carrying integron among Enterobacteriaceae isolates in Mexico: report from the SENTRY Antimicrobial Surveillance Program

Abstract number: P901

Deshpande L., Jones R., Morfin-Otero R., Rodriguez E., Sader H.

Objectives: To characterise metallo-b-lactamase (MBL)-producing Enterobacteriaceae (ENT) strains isolated in a Mexican hospital and to evaluate the genetic context of the MBL-encoding genes. Carbapenems are generally very active against ENT but resistance has been emerging and has increased rapidly in some geographic areas due to the dissemination of MBL-carrying integrons.

Methods: ENT collected as part of the SENTRY Antimicrobial Surveillance Program were susceptibility (S) tested against >25 antimicrobials by CLSI broth microdilution methods. Isolates with imipenem and/or meropenem MIC at geqslant R: gt-or-equal, slanted2 mg/L were screened for MBL production by the disk approximation test; positive isolates were further characterised by PCR and gene sequencing. Primers targeting the class 1 integron conserved structures anchoring MBL genes were used to reveal integron structure. Amplicons generated were sequenced on both strands and MBL-producing isolates were evaluated for possible clonality by PFGE.

Results: Three isolates, all from one hospital in Mexico, exhibited positive MBL-screening test results. Two E. cloacae (2005 and 2007) and one K. oxytoca (2006) yielded a PCR product with blaVIM primers. The MBL gene was embedded in a 2.8-Kb class 1 integron in all strains. Sequencing revealed that blaVIM-2 was located in the first position of the integron followed by 2 gene cassettes: an open reading frame (orf) and an aminoglycoside acetyl transferase gene (aacA7). The 400-bp orf showed low homology with other DNA sequences; however the deduced amino acid sequence showed active domains of a chorismate mutase enzyme from Pseudomonas fluorescens. The degree of carbapenem resistance varied significantly among these VIM-2-producing isolates. The E. cloacae isolates were epidemiologically unrelated and one strain was S to both imipenem and meropenem (ertapenem also S; 0.12 or 0.25 mg/L) based on current CLSI breakpoints of leqslant R: less-than-or-eq, slant4 mg/L (see Table).

Conclusions: The finding of distinct ENT strains over a period of 3 years harbouring the same blaVIM-2-carrying integron indicates that this mobile genetic structure has become locally endemic. MBL-producing ENT may not be detected by clinical microbiology laboratories due to S-level carbapenem and other b-lactam MIC results, requiring new detection strategies or revised S breakpoints.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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