From May 1996 to September 1997, 615 Pseudomonas aeruginosa strains isolated from patients in intensive care units collected from different Italian laboratories were studied. The susceptibility of piperacillin/tazobactam, in comparison with other antipseudomonal antibiotics, to their NCCLS breakpoints was evaluated: amikacin 79.6%, carbenicillin 67.0%, ceftazidime 73.4%, ciprofloxacin 55.8%, imipenem 64.1%, piperacillin 88.1%, piperacillin/tazobactam 92.4% and ticarcillin/clavulanic acid 69.0%. Seventy-three strains were selected because of their resistance to piperacillin and the mechanisms underlying such a resistance were investigated. Isoelectric focusing and hydrolysis assays revealed the presence of 15 plasmid-mediated β-lactamases. Chromosomal β-lactamase derepression was demonstrated in 34 isolates. The remaining 24 piperacillin-resistant strains did not produce β-lactamases and an 'intrinsic mechanism' of resistance was inferred. The piperacillin/tazobactam combination restored resistance in 25 piperacillin strains. Nine of these were derepressed for chromosomal β-lactamase, 8 showed impermeability and 8 showed plasmid enzymes.
In vitro activity of piperacillin/tazobactam against 615 Pseudomonas aeruginosa strains isolated in intensive care units
FRANCESCHINI, Nicola;PERILLI, MARIAGRAZIA;AMICOSANTE, Gianfranco;
1998-01-01
Abstract
From May 1996 to September 1997, 615 Pseudomonas aeruginosa strains isolated from patients in intensive care units collected from different Italian laboratories were studied. The susceptibility of piperacillin/tazobactam, in comparison with other antipseudomonal antibiotics, to their NCCLS breakpoints was evaluated: amikacin 79.6%, carbenicillin 67.0%, ceftazidime 73.4%, ciprofloxacin 55.8%, imipenem 64.1%, piperacillin 88.1%, piperacillin/tazobactam 92.4% and ticarcillin/clavulanic acid 69.0%. Seventy-three strains were selected because of their resistance to piperacillin and the mechanisms underlying such a resistance were investigated. Isoelectric focusing and hydrolysis assays revealed the presence of 15 plasmid-mediated β-lactamases. Chromosomal β-lactamase derepression was demonstrated in 34 isolates. The remaining 24 piperacillin-resistant strains did not produce β-lactamases and an 'intrinsic mechanism' of resistance was inferred. The piperacillin/tazobactam combination restored resistance in 25 piperacillin strains. Nine of these were derepressed for chromosomal β-lactamase, 8 showed impermeability and 8 showed plasmid enzymes.Pubblicazioni consigliate
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