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By in vitro tests on 12 strains of Pseudomonas aeruginosa, sputum from patients with cystic fibrosis sharply increased the minimal bactericidal concentrations of polymyxin B and neomycin. Sputum had a lesser effect on tests with gentamicin and tobramycin and essentially none on tests with carbenicillin.
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Davis et al. (1978) studied this question.