Selective pressure of tetracyclines on the faecal flora. A comparison between tetracycline and doxycycline.

The aerobic faecal flora was studied in two groups of healthy adult persons, each group consisting of 18 individuals, before a course of either doxycycline or tetracycline HCI, at the cessation of therapy and 5 weeks afterwards. The main object of this study was to evaluate the effect of antibacterial treatment on the occurrence of mutagenic resistant and plasmid carried resistant strains in the faecal flora, and in particular development of resistant E. coli. The frequency of resistant strains increased after treatment with both of the drugs without significant differences.