Molecular surveillance of European quinolone-resistant clinical isolates of Pseudomonas aeruginosa and Acinetobacter spp. using automated ribotyping

Abstract

Nosocomial isolates of Pseudomonas aeruginosa and Acinetobacter spp. exhibit high rates of resistance to antibiotics and are often multidrug resistant. In a previous study (D. Milatovic, A. Fluit, S. Brisse, J. Verhoef, and F. J. Schmitz, Antimicrob. Agents Chemother. 44:1102-1107, 2000), isolates of these species that were resistant to sitafloxacin, a new advanced-generation fluoroquinolone with a high potency and a broad spectrum of antimicrobial activity, were found in high proportion in 23 European hospitals. Here, we investigate the clonal diversity of the 155 P. aeruginosa and 145 Acinetobacter spp. sitafloxacin-resistant isolates from that study by automated ribotyping. Numerous ribogroups (sets of isolates with indistinguishable ribotypes) were found among isolates of P. aeruginosa (n = 34) and Acinetobacter spp. (n = 16), but the majority of the isolates belonged to a limited number of major ribogroups. Sitafloxacin-resistant isolates (MICs > 2 mg/liter, used as a provisional breakpoint) showed increased concomitant resistance to piperacillin, piperacillin-tazobactam, ceftriaxone, ceftazidime, amikacin, gentamicin, and imipenem. The major ribogroups were repeatedly found in isolates from several European hospitals; these isolates showed higher levels of resistance to gentamicin and imipenem, and some of them appeared to correspond to previously described multidrug-resistant international clones of P. aeruginosa (serotype O:12) and Acinetobacter baumannii (clones I and II). Automated ribotyping, when used in combination with more discriminatory typing methods, may be a convenient library typing system for monitoring future epidemiological dynamics of geographically widespread multidrug-resistant bacterial clones.

FIG. 1

Overview of the 52 distinct PvuII ribotypes obtained after ribotyping of 203 P. aeruginosa clinical isolates, including 155 sitafloxacin-resistant isolates. The number of isolates falling in each ribogroup and the number of centers where a ribogroup was collected are indicated only when the numbers were >1. The serotype(s) determined for one or more strains within each ribogroup is indicated. Several isolates were serotyped only for ribogroups 210-88-5, 210-87-3, and 210-87-2. For cluster analysis, UPGMA was used based on the matrix of Pearson correlation coefficients. In the dendrogram scale, correlation levels were converted to percent similarity levels. Four dominant ribogroups, with 15 to 43 isolates, were found, with the most prevalent one being 210-87-3, which corresponds to the widespread genotype serotype O:12 (31, 41). NT, nontypeable; nd, not determined.

FIG. 2

Overview of the 21 distinct EcoRI ribotypes obtained after the ribotyping of 159 Acinetobacter spp. clinical isolates, including 145 sitafloxacin-resistant isolates. The number of isolates falling in each ribogroup is indicated only when the number was >1. The DG or taxonomic species of reference strains analyzed for comparison are given on the right of the ribogroup to which they belong. Ribotypes of outbreak clones I and II (18) are indicated. Strain ATCC 19606^T, the type strain of A. baumannii, fell in ribogroup 210-52-7. The asterisks indicate that the species or DG was deduced based on the correspondence of patterns with those published previously (21, 43). DG 13TU, DG 13 sensu Tjernberg and Ursing (51). For cluster analysis, UPGMA was used based on the matrix of Pearson correlation coefficients. In the dendrogram scale, correlation levels were converted to percent similarity levels.