Occurrence of antipseudomonal beta-lactams and aminoglycosides resistance in Pseudomonas aeruginosa during therapy.

Four strains of Pseudomonas aeruginosa clinical isolates were studied for resistance to antipseudomonal beta-lactams and aminoglycosides. Two of these strains were isolated from two different patients before antibiotic treatment, the other two strains, isolated during therapy, developed resistance to many of antipseudomonal beta-lactams and, in addition, to aminoglycoside antibiotics. All the strains produced a constitutive chromosomal beta-lactamase, while the latter two showed a significant reduction in permeability coefficient. Thus, a permeability change may be the major factor involved in the resistance to most antipseudomonal beta-lactams and may be responsible for development of cross-resistance to aminoglycosides.