Peña C, Suarez C, Tubau F, Juan C, Moya B, Dominguez MA, Oliver A, Pujol M, Ariza J
Nosocomial outbreak of a cefepime-nonsusceptible ceftazidime-susceptible Pseudomonas aeruginosa strain overexpressing MexXY-OprM and producing an integron-borne PSE-1 ss-lactamase. [JOURNAL ARTICLE]
J Clin Microbiol 2009 Jun 3.
Cefepime (FEP) and ceftazidime (CAZ) are broad-spectrum cephalosporins that display similar MICs for wild-type Pseudomonas aeruginosa. Recently in our hospital, P. aeruginosa isolates showing susceptibility discordance of CAZ versus FEP have been noted and a clustering was suspected. During the study period (March-December 2007), 51 patients, particulary those in intensive care unit (ICU) [29 (57%)], with at least one P. aeruginosa FEP-nonsusceptible/CAZ-susceptible (FEP(NS)/CAZ(S)) phenotype strain were detected. 23 (45%) were infected and respiratory tract was the most frequent infection. Changes in the consumption of antimicrobials in the ICUs were observed over time: a progresive reduction in carbapenems (247 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 piperacillin-tazobactam use (42 DDD/1,000 patient-days in 2004 to 200 DDD/1,000 patient-days in 2007; p<0.001). A single clone of P.aeruginosa FEP(NS)/CAZ(S) phenotype strain, associated with the hyperexpression of MexXY-OprM and the production of an integron-borne PSE-1 ss-lactamase, was identified by pulsed-field gel electrophoresis analysis throughout the whole period. In conclusion, we identified an epidemic P. aeruginosa clone of FAP(NS)/CAZ(S) phenotype strain involving 51 patients, particulary ICU patient. The combination of overexpressing 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 emergence and spread of this P. aeruginosa strain.
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