The effect of amoxycillin on vaginal colonization resistance and normal vaginal flora in monkeys

Previous studies have shown that vaginal colonization resistance in monkeys can be eliminated by amoxycillin and restored by flushing vaginal flora from a healthy monkey into the vagina of a monkey colonized with Escherichia coli. The hypothesis that the effect of amoxycillin resulted from elimination of parts of the normal flora was tested in the present study. Nine monkeys were flushed vaginally with amoxycillin daily for six days. The number of anaerobic bacteria decreased during amoxycillin administration, as did the number of species isolated. The most obvious effects were observed among the genera Bacteroides and Peptostreptococcus, while Lactobacillus spp. were less affected. Restoration of the flora after amoxycillin administration was slow in most of the monkeys. During amoxycillin administration, all monkeys became colonized spontaneously with E. coli. This was not, however, associated with increased adherence in vitro. The colonization persisted throughout the study period (29 days). It was concluded that amoxycillin disturbs vaginal colonization resistance by eliminating at least part of the normal vaginal flora, thereby promoting periurethral colonization with enterobacteria.