Drug resistance and plasmid mediated transfer of drug resistance in Escherichia coli isolated from various districts of the human organism. A possible relationship with the antimicrobial drug concentrations during therapy.

The study of the prevalence of drug resistances and of the frequency of R factors among resistant strains, in E. coli isolated respectively from the respiratory, intestinal and urinary tracts of patients, during 1976, has shown that the frequency of drug resistances is highest among E. coli strains isolated from the respiratory tract and lowest among the E. coli strains isolated from urines. The frequency of R factors, among resistant strains, follows an exactly opposite distribution. This behaviour could be related to the gradient of antimicrobial drug concentrations achieved in the various compartments during ordinary antimicrobial therapy.