Transferable antibiotic resistance in enteropathogenic Escherichia coli between 1948 and 1968

Enteropathogenic strains of Escherichia coli which had been isolated in the United Kingdom during three periods between 1948 and 1968, namely 1948 to 1951, 1957 to 1960, and 1967 to 1968, were tested for susceptibility to ampicillin, streptomycin, tetracycline, chloramphenicol, and sulphonamides. Antibiotic-resistant strains were tested for their ability to transfer antibiotic resistance to an antibiotic-susceptible strain of E. coli K-12. A relatively high proportion of strains isolated between 1948 and 1951 was resistant to ampicillin, streptomycin, or sulphonamides. None of these strains transferred ampicillin or streptomycin resistance, but sulphonamide resistance was R-factor-mediated in three out of 14 sulphonamide-resistant strains. Resistance to tetracycline and chloramphenicol was rare before 1951 but had become common among enteropathogenic E. coli by 1957. Much of the antibiotic resistance of bacteria isolated between 1957 and 1960 was R-factor-mediated, and transferable resistance was about as prevalent among E. coli isolated between 1957 and 1960 as among strains isolated in 1967 and 1968. Nevertheless, there was no appreciable increase in the overall incidence of antibiotic resistance among these enteropathogenic strains of E. coli between 1957 and 1968, although transferable antibiotic resistance was common during this period. These results do not suggest that the emergence of transferable antibiotic resistance will inevitably lead to the rapid development of antibiotic resistance among this group of bacteria.