Abstract

Sensitivity tests with 12 antibiotics on 1,018 strains of Gram-negative bacilli isolated in a burns unit between 1969 and 1971 showed some important differences from results in similar tests on a series of strains isolated between 1965 and 1967. These changes included the emergence of a large proportion of kanamycin-resistant strains of Klebsiella aerogenes, Proteus mirabilis, and Escherichia coli and of smaller proportions of trimethoprim- and gentamicin-resistant strains; also the complete replacement of Proteus mirabilis with dissociated resistance to ampicillin by strains showing linked resistance to ampicillin and carbenicillin. The probable relationship of these changes to the emergence of an R factor determining resistance to tetracycline, kanamycin, carbenicillin, ampicillin, and cephaloridine in Enterobacteria and Pseudomonas aeruginosa is discussed.