Resistance of Pseudomonas aeruginosa to gentamicin.

The resistance to gentamicin 4 mug./ml. of 250 Pseudomonas aeruginosa isolates was measured by a proportion method. Twenty-eight (11.2%) of the cultures fell into the most resistant group, in whose populations between 10 and 100% of the organisms were resistant. A relatively high percentage of urinary isolates and a comparatively low percentage of isolates from respiratory sources occurred in this group. Three of the 28 were resistant to carbenicillin 150 mug./ml. and 6 of 18 tested were as resistant to gentamicin 8 mug./ml. as they were to 4 mug./ml. The distribution of Ps. aeruginosa isolates between the different grades of resistance did not change significantly during the 10 months in which the survey was performed.