Prevalence of Mex-mediated resistance in Pseudomonas aeruginosa isolates from patients with ventilator-associated pneumonia in 4 Belgian hospitals

Abstract number: 1733_855

Dediste A., Van Laethem Y., Jacobs F., Struelens M., De Vos D., Pirnay J., Van Bambeke F., Tulkens P., Mesaros N., Glupczynski Y., Pierard D.

Objectives: Efflux mediated resistance is difficult to detect in Pseudomonas aeruginosa (Pa) by routine susceptibility testing. Yet, it may confer cross-resistance to unrelated classes of drugs and contribute to selection of other resistance mechanisms. Our aim was to determine the prevalence of Mex efflux pumps in Pa isolates obtained from patients with ventilator-associated pneumonia (VAP).

Methods: Pa isolates were collected as pairs from each patient (first isolate before initiation of antibiotic treatment [pre]; second isolate, after 5 to 10 days of treatment [post]). In three hospitals (A-C), isolates were collected consecutively from all eligible patients; in the 4th hospital (D), isolates were selected on the basis of compatible resistance phenotypes. mexA and mexX transscription levels were quantified by real time PCR; mexC and mexE transcription was detected by semi-quantitative PCR (their basal expression being undetectable in wild-type strains). Isolates typing was performed by fAFLP.

Results: The table shows the number of isolates in which overexpression of mex genes was detected (pre and post) by hospital. DNA-based typing globally confirmed the clonality of the sucessive isolates in each patient, and excluded the occurrence of epidemic strains in the non-selected isolates.

Hospitala (no. of pairs)No. of strains showing gene overexpression
Random sampling
A (n = 9)01100047
B (n = 7)01562313
C (n = 6)00000000
Total (n = 22)026623510
Strains collected on the basis of compatible resistance phenotype
D (n = 17)28450479
aA, AZ-Vrije Universiteit Brussels, B, CHU Saint-Pierre; C, Hôpital Erasme; D, Clinique universitaire UCL Mont-Godinne.

Conclusions: A variable prevalence of Mex efflux pumps is found before treatment in clinical isolates, and increases in several cases following antibiotic exposure, particularly for MexX. In samples collected based on antibiograms, prevalence was very high, confirming the value of the interpretive algorithms used to detect mechanisms of efflux resistance. These data highlight the need of detecting efflux-mediated resistance in Pa clinical isolates originating from hospitalised ICU patients.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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