Transferable Resistance to Antibiotics in Gram-Negative Bacteria Isolated in a Hospital for Infectious Diseases: I. Occurrence and Multiple Origin of R Factors

Abstract

The occurrence and origin of R factors was studied in multiple antibiotic-resistant gram-negative bacteria isolated from in-patients at Roslagstull Hospital, Stockholm. During a 2-month period 148 polyresistant strains were found among a total of 511 gram-negative strains tested. A frequency of R factors of 29% was found. In 7 out of 8 species investigated transfer of antibiotic resistance to E. coli C was observed. Of the 42 R factor-carrying strains 9 transferred resistance to tetracycline only. One E. coli strain transferred simultaneously resistance to 7 antibiotics. Transfer of resistance to tetracycline and sulfonamide was most frequently observed whereas transfer of furantoin resistance was very uncommon. On the basis of the many different combinations of drug resistance transferred and the different influences of the R factors on the sensitivity of their host to phages it is concluded that the R factors found in this hospital were of multiple origins. Transferable resistance is now studied from an epidemiological point of view.