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The effects of orally administered penicillin and tetracycline on the composition of the normal throat flora and its interference with the growth of group A streptococci were evaluated by throat culture and an agar overlay technique. Tetracycline caused only a slight, transient quantitative decrease in the composition of the flora and interference activity. Penicillin caused significant quantitative and qualitative decreases in both the composition of the flora and interference activity. The diminution in interference activity persisted up to 3 weeks after therapy. The differences observed between the antibiotic regimens correlated with differences in initial susceptibility of the flora to the antibiotic used and emergence of the resistance during therapy. Results indicated that although effects of antibiotics on the composition of the flora are transient, effects on its ability to interfere with group A streptococci may persist long after therapy is discontinued. It is thus possible that penicillin therapy may enhance susceptibility of certain individuals to subsequent infection with group A streptococci.

1. The effect of tetracyclines on the isolated dog ureter is dependent on: (a) the tetracyclines used-mepicycline and doxycycline antagonizing, and tetracycline and rolitetracycline increasing the contractor action of barium chloride; (b) the percentage of 4-epiderivatives in the tetracyclines used-the higher the epiderivative concentration, the smaller the effect of mepicycline or doxycycline, and the greater the action of tetracycline or rolitetracycline.2. In vivo the addition of the antibiotics into the renal pelvis shows no significant differences between the various tetracyclines or different 4-epiderivative concentrations on the intra-ureteral flow of the dog or guinea-pig.3. Intravenous injection of mepicycline or doxycycline does not induce a significant change in the intra-ureteral flow, while intravenous administration of tetracycline or rolitetracycline produces a triphasic response: (a) a marked decrease of the intra-ureteral flow for a few minutes; (b) a return to the control condition for 30-60 min; and (c) a lesser but persistent decrease in flow for 60-120 minutes. In the first phase the ureteral smooth muscle is directly affected by the antibiotics circulating in the blood, while in the third phase the tetracyclines act via the intra-ureteral mucosa.4. Neurogenic effects on the ureter-bladder junction in vivo are not affected by the tetracyclines tested.

The faeces from 100 children under 14 years receiving no antibiotic or steroid therapy were examined for Candida spp. The proportion (8%) of positive isolates is compared with the number of Candida spp. isolated from the faces of 50 children receiving oral tetracycline (14%) and 59 children on phenoxymethyl penicillin (10%) for complaints other than gastrointestinal infections. The use of selective media is described and the significance of the greatly increased numbers of Candida spp. found by these methods is discussed. In this series no clinical manifestations of candidiasis were observed, although slightly more Candida spp. were recovered from the two groups of children on oral antibiotics than from those not on such therapy. It is suggested that, in children at least, there is a need to re-assess the significance of the presence of Candida in the bowel during the administration of oral antibiotics. The almost complete absence of active tetracycline from the faeces and the small proportion of tetracycline-sensitive bowl organisms, coupled with the low incidence of change in bowel flora in these patients, suggest that this is not the reason for proliferation of Candida in the cases that do occasionally occur.