Genetic structure at the origin of acquisition of blaOXA-18 gene, encoding an emerging class D clavulanic-acid inhibited extended-spectrum b-lactamase

Abstract number: O209

Naas T., Bogaerts P., Namdari F., Huang T., Glupczynski Y., Nordmann P.

Objectives:Pseudomonas aeruginosa (Pa) is an important nosocomial pathogen that may acquire resistance to expanded-spectrum cephalosporins mostly by overproducing its cephalosporinase and/or acquiring Ambler class A, B and D b-lactamases. Several clavulanic acid-inhibited Ambler class A extended-spectrum b-lactamases (ESBLs) and extended-spectrum class D enzymes (OXA-ESBLs) have been isolated in Pa. OXA-18 is a peculiar OXA-ESBL, since it is not a point mutant derivative of broad-spectrum OXA enzymes and is well inhibited by clavulanic acid. It was initially reported along with OXA-20 in Pa MUS from France in 1996, and very recently in several Pa isolates involved in an outbreak in Tunisia.

Methods: Genetic structures surrounding the blaOXA-18 gene of the prototype Pa MUS strain were characterised by cloning, PCR analysis and sequencing and compared with those found in three Pa isolates from Belgium. The strains were analysed by plasmid extraction, conjugation and electroporation assays, and by PFGE.

Results: The three Belgian isolates originated from sputum and blood specimens of three patients hospitalised in different wards over a six-month period. The presence of ESBLs detected by double-disk diffusion tests on cloxacillin-containing plates, and PCR followed by sequencing revealed the presence of blaOXA-18 and blaOXA-20 genes. Both were chromosomally-encoded and PCR mapping revealed identical genetic environments for Pa MUS and the Belgian isolates. While most oxacillinases are integron located, blaOXA-18 lacked gene cassette specific sequences but was inserted into an aac6' Ib gene cassette. In addition, it was bracketed by two novel insertion sequences of ISCR family. It is likely that these ISs were at the origin of the blaOXA-18 gene mobilisation. Furthermore, detailed analysis of an 8.5-kb cloned genomic fragment containing blaOXA-18 gene revealed co-linearity of the blaOXA-18 gene and the integron containing blaOXA-20 gene. PFGE defined genetic relatedness between the three Belgian Pa isolates and Pa MUS strain. The recently identified OXA-18-producing Pa isolates from Tunisia were blaOXA-20-negative (but positive for either TEM-1 or SHV-1), genetically different from Pa MUS, thus suggesting that at least two OXA-18-producing Pa clones are currently spreading.

Conclusion: This report characterised the genetic elements at the origin of blaOXA-18 ESBL in Pa and suggests the emergence of this type of ESBLs in Pa in Belgium.

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:
Back to top