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Journal of Clinical Microbiology, August 2005, p. 4129-4138, Vol. 43, No. 8
0095-1137/05/$08.00+0 doi:10.1128/JCM.43.8.4129-4138.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Laboratoire de Microbiologie, Faculté de Pharmacie, EA 525, Université de Bordeaux 2, Bordeaux, France,1 Laboratoire d'Analyses Médicales, Villenave d'Ornon, France2
Received 3 March 2005/ Returned for modification 23 March 2005/ Accepted 12 April 2005
Over a 6-year period, 24 extended-spectrum ß-lactamase (ESBL)-producing isolates of Pseudomonas aeruginosa were collected from 18 patients living in a nursing home. These isolates had a delayed development of a red pigment and exhibited a similar antibiotype (resistance to all ß-lactams except for imipenem and to gentamicin, tobramycin, netilmicin, ciprofloxacin, and rifampin) associated with the production of the TEM-21 ß-lactamase and a type II 3'-N-aminoglycoside acetyltransferase [AAC(3)-II] enzyme. Surprisingly, serotyping showed that these isolates belonged to four successive serotypes (P2, P16, P1, and PME), although molecular typing by PCR methods and pulsed-field gel electrophoresis yielded identical or similar profiles. Moreover, in all isolates the blaTEM-21 gene was part of a chromosomally located Tn801 transposon truncated by an IS6100 element inserted within the resolvase gene, and the aac(3)-II gene was adjacent to this structure. During the same period, 17 ESBL-producing isolates of enterobacteria were also collected from 10 of these patients. These isolates harbored a similar large plasmid that contained the blaTEM-21 and the aac(3)-II genes and that conferred additional resistance to sulfonamides and chloramphenicol, as well as to kanamycin, tobramycin, netilmicin, and amikacin, conveyed by an AAC(6')-I enzyme. The blaTEM-21 gene was part of the Tn801 transposon disrupted by IS4321. Thus, a single clone of P. aeruginosa that had undergone a progressive genetic drift associated with a change in serotype appeared to be responsible for an outbreak of nosocomial infections in a nursing home. This strain has probably acquired the blaTEM-21-encoding plasmid that was epidemic among the enterobacteria at the institution, followed by chromosomal integration and genomic reorganization.
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