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Journal of Clinical Microbiology, August 2009, p. 2381-2387, Vol. 47, No. 8
0095-1137/09/$08.00+0     doi:10.1128/JCM.00094-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Nosocomial Outbreak of a Non-Cefepime-Susceptible Ceftazidime-Susceptible Pseudomonas aeruginosa Strain Overexpressing MexXY-OprM and Producing an Integron-Borne PSE-1 ß-Lactamase{triangledown}

C. Peña,1* C. Suarez,1 F. Tubau,2,3 C. Juan,4 B. Moya,4 M. A. Dominguez,2 A. Oliver,4 M. Pujol,1 and J. Ariza1

Infectious Diseases Service,1 Microbiology Service, IDIBELL, Hospital de Bellvitge, University of Barcelona, Barcelona, Spain,2 Ciber de Enfermedades Respiratorias, ISCIII, Madrid, Spain,3 Microbiology Service, Hospital Son Dureta, Palma de Mallorca, Spain4

Received 16 January 2009/ Returned for modification 13 March 2009/ Accepted 29 May 2009

Cefepime (FEP) and ceftazidime (CAZ) are broad-spectrum cephalosporins that display similar MICs for wild-type Pseudomonas aeruginosa strains. Recently, P. aeruginosa isolates showing a discordance in susceptibility to CAZ and FEP have been noted at the Hospital de Bellvitge in Barcelona, Spain, and a clustering was suspected. During the study period (March to December 2007), 51 patients, particularly those in an intensive care units (ICUs) (n = 29 [57%]), infected or colonized with at least one P. aeruginosa non-FEP-susceptible and CAZ-susceptible (Fepns Cazs) phenotype strain were detected. Twenty-three (45%) patients were infected, and the respiratory tract was the most frequent site of infection. Changes in the consumption of antimicrobials in the ICUs were observed over time: a progressive reduction in the levels of consumption of carbapenems (247 defined daily doses [DDD]/1,000 patient days to 66 DDD/1,000 patient days; P = 0.008), after restriction of its use in 2006, and an expected increase in the rate of piperacillin-tazobactam use (42 DDD/1,000 patient days in 2004 to 200 DDD/1,000 patient days in 2007; P < 0.001). Throughout the whole study period, only a single clone of a P. aeruginosa Fepns Cazs phenotype strain was identified by pulsed-field gel electrophoresis analysis to be associated with the hyperexpression of MexXY-OprM and the production of an integron-borne PSE-1 ß-lactamase. In conclusion, we identified an epidemic P. aeruginosa clone of an Fepns Cazs phenotype strain involving 51 patients, in particular, ICU patients. The combination of the overexpression of an efflux pump and PSE-1 ß-lactamase production is associated with the multidrug-resistant phenotype. The dominant use of a single class of antibiotics could have provided the selective pressure required for the emergence and spread of this P. aeruginosa strain.

* Corresponding author. Mailing address: Infectious Diseases Service, Hospital de Bellvitge, Feixa Llarga s/n, 08907 L'Hospitalet de Llobregat, Barcelona, Spain. Phone: 34-932607625. Fax: 34-932607637. E-mail: cpena{at}csub.scs.es

{triangledown} Published ahead of print on 3 June 2009.

Journal of Clinical Microbiology, August 2009, p. 2381-2387, Vol. 47, No. 8
0095-1137/09/$08.00+0     doi:10.1128/JCM.00094-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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