Pseudomonas aeruginosa isolates from different medical institutions.

Patients screened for antibiotic resistance at three different medical institutions yielded 1,597 isolates of Pseudomonas aeruginosa. Most of the isolates were sensitive to amikacin (92.8%), tobramycin (70.6%), gentamicin (59.1%) neomycin (89.4%), azlocillin (84.6%), mezlocillin (83.9%), piperacillin (85.7%), cefsulodin (83.8%) and colistin (98.5%); only 43.8% were sensitive to carbenicillin. In a rehabilitation hospital the frequency of isolates resistant to most of these antibiotics was twice as high than in the two other institutions. The frequency of phenotypes resistant to the combination of carbenicillin and gentamicin was twice as high in the rehabilitation hospital isolates (47.3%) than in the general hospital isolates (28.5%). The frequency of isolates resistant to the combination of aminoglycosides and the new beta-lactam antibiotics is relatively lower than in the former combinations. Serogroup 11 is predominant in the isolates from all three institutions (44%). In carbenicillin- and gentamicin-resistant isolates, 61% were of serogroup 11. On the other hand, in the carbenicillin- and gentamicin-sensitive isolates, serogroup 11 accounted for only 27.2%.