Effect of oral spiramycin on the faecal and oral bacteria in human volunteers.

Six healthy adult volunteers were treated with 1 g of oral spiramycin twice daily for five days, and their oral and faecal microbial flora were studied. Mean saliva and serum concentrations of the antibiotic never exceeded 2.1 +/- 1.1 mg/l. The number of volunteers whose oral cavity was colonized by Enterobacteriaceae, group D streptococci, staphylococci, and fungi remained unchanged following treatment. The mean count of anaerobic faecal bacteria was 10.3 +/- 0.6 log10 cfu/g initially. This did not change significantly during the treatment, nor did the composition of the predominant anaerobic flora. Mean counts of group D streptococci were 1000 times lower than those of anaerobes before treatment, and also remained unchanged during therapy. No overgrowth of fungi, staphylococci, or Pseudomonas aeruginosa was observed. No significant modifications occurred in the mean total count of faecal Enterobacteriaceae (7.9 +/- 0.4 versus 7.4 +/- 1.0 log10 cfu/g of faeces before and during treatment respectively). However, faecal concentrations of highly spiramycin-resistant Enterobacteriaceae (MIC greater than or equal to 512 mg/l) increased from 4.8 +/- 1.2 to 7.0 +/- 1.8 log10 cfu/g during treatment. The MIC50 value of spiramycin for anaerobes, Enterobacteriaceae, and group D streptococci were 0.125, 64, and 0.5 mg/l respectively before treatment, and these increased to 1024, 512 and 1024 mg/l respectively during treatment. This was attributed to the rise in the faecal concentrations of spiramycin, which reached 689 +/- 48 micrograms/g of faeces on the fifth day of treatment. These concentrations decreased rapidly on cessation of treatment.