Sensitivity of Respiratory Strains of Pseudomonas Aeruginosato Carbenicillin

The MIC of carbenicillin for 111 strains of Pseudomonas aeruginosa isolated from the sputum of patients with chronic respiratory infections was estimated. For 72 strains it corresponded to that reported for strains isolated from nonrespiratory sites (25−> 100 µg per ml), but for 39 strains it ranged from 6 µg per ml to <0.7 µg per ml.

About half of the strains were typed serologically, by bacteriophages and by pyocine production. No evidence for cross-infection between the patients was found, nor was there any correlation between sensitivity to carbenicillin and any particular type of organism.

There was no evidence that strains with an abnormally low MIC were more virulent in the respiratory tract than were strains with an “ordinary” MIC; nor did it appear that coexistence with enterobacteria in the respiratory tract affected the carbenicillin resistance of P. aeruginosa.