Antibiotic Resistance and R Factors in Gram-Negative Bacteria Isolated in a Hospital for Infectious Diseases: III. The Effect of Antibacterial Treatment on the Incidence of R Factor-Mediated Antibiotic Resistance

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Abstract
A survey of the incidence of antibiotic-resistant and R factor-carrying enteric bacteria in the intestinal flora of healthy subjects in Stockholm is presented. A total of 377 strains were isolated from 266 individuals; 169 of them carried one or more resistant strains. Of these strains 135 were classified as Escherichia coli. Resistant E. coli dominated the faecal flora in 101 persons. Only about 50% of the resistant strains were multiresistant, i.e. resistant to more than two antibiotics. R factors were found in 24% of all resistant strains and in 47% of the multiresistant ones. After treatment with antibiotics the frequency of resistant enteric bacteria was increased significantly when either sulfaisodimidine, ampicillin, erythromycin, or tetracycline was given. The incidence of R factor-mediated resistance was significantly increased only in strains isolated from persons treated with tetracycline.