Emergence of ceftriaxone-resistant strains of Pseudomonas aeruginosa in cystic fibrosis patients

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Abstract
Cystic fibrosis patients with Pseudomonas aeruginosa chest infections were treated with ceftriaxone alone or ceftriaxone plus tobramycin. P. aeruginosa strains isolated before and after treatment were studied for changes in sensitivity to ceftriaxone. After therapy with either the single agent or the combination six strains from five patients were found to be resistant to ceftriaxone. No resistant strains were isolated before therapy. Resistance was mediated by excess production of Id β-lactamase which in five of six strains was permanently derepressed. Bacterial resistance appearing during therapy reduces the value of this antibiotic in cystic fibrosis chest infections.