Multifocal Detection of Multidrug-Resistant Pseudomonas aeruginosa Producing the PER-1 Extended-Spectrum β-Lactamase in Northern Italy

ABSTRACT

Forty-four nonreplicate clinical isolates of Pseudomonas aeruginosa that were resistant to extended-spectrum cephalosporins (ceftazidime and cefepime) and aztreonam, that putatively produced an acquired extended- spectrum β-lactamase (ESBL), according to the results of a double-disk synergy test, and that had been involved in nosocomial outbreaks were obtained from six different hospitals in northern Italy and screened for the presence of bla_PER ESBL determinants. Twenty isolates, associated with nine independent outbreaks that occurred in five hospitals in the Milan area and its surroundings during 1995-2000, were found to carry an acquired bla_PER-1 gene. PER-1 producers representative of the nine outbreaks exhibited a multidrug resistance (MDR) phenotype, including resistance to extended-spectrum cephalosporins, aztreonam, meropenem, aminoglycosides, and in most cases, imipenem and ciprofloxacin. An analysis of macrorestriction profiles of their genomic DNAs by pulsed-field gel electrophoresis revealed an overall clonal diversity of the PER-1 producers, although interhospital clonal spread was also observed. The bla_PER-1 gene was not transferable and appeared to be chromosomally located. An analysis of the EcoRI and EcoRV restriction fragment length polymorphisms of the bla_PER-1 locus revealed identical patterns for all isolates, and the characterization of a 1.9-kb region containing bla_PER-1 revealed a conserved structure in representatives of the various clonal lineages. The present findings indicate that MDR P. aeruginosa clones producing the PER-1 ESBL are endemic to this area of northern Italy, where they have been circulating since the mid-1990s and have been associated with several nosocomial outbreaks.