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The faecal excretion of short-chain fatty acids (SCFAs) has been measured in groups of six healthy subjects before, during, and after they received the antibiotics clindamycin, ampicillin, or metronidazole perorally for 6 days. Intake of clindamycin reduced the median total concentration of SCFAs from 62.9 mmol/kg faeces (wet weight) to 7.3 mmol/kg (p less than 0.05). During therapy the relative amounts of acetic acid increased from 50% to 90% of the total concentration (p less than 0.05). Ampicillin reduced the median SCFAs concentration from 62.4 mmol/kg to 47.8 mmol/kg (p less than 0.05), whereas metronidazole did not change the SCFAs concentrations significantly. The SCFAs concentrations returned to normal within 5 weeks after the treatment in all subjects. Clindamycin was detected in high concentrations in faeces during therapy. Ampicillin was detected in only one faecal sample, which was from the only subject in the ampicillin group without detectable beta-lactamase activity in faeces. Metronidazole could not be detected in faeces from any subjects receiving this drug. Clindamycin and ampicillin, but not metronidazole, induce pronounced changes in faecal SCFAs, most likely reflecting severe changes in the colonic ecosystem. An antibiotic's influence on the colonic microflora may in part depend on its antimicrobial spectrum and the concentration of antimicrobially active drug in the gut.

This report presents a new approach to the study of the colonization of the digestive tract after birth. We have examined the development of four microflora associated characteristics, MACs, defined as the recording of any anatomical structure, biochemical or physiological function in the macroorganism, which has been influenced by the microflora. These MACs may create a basis for later investigations into the impact of diarrheal diseases and antibiotic therapy. The following biochemical characteristics were studied in feces from children of 0-61 months of age: conversion of cholesterol to coprostanol and bilirubin to urobilins, inactivation of trypsin and degradation of mucin. These results indicate establishment of microbes capable of converting bilirubin to urobilins within the second year of life. The mucin degrading and cholesterol converting microbes are established in most of the children during the same period. Tryptic activity was found to be absent in meconium, present in feces from all children up to 21 months of age, and absent in 6 out of 15 children in the age group 46-61 months. The study indicates that the establishment of the MACs in the digestive tract is a remarkably long drawn out process.

The intestinal microbial conversion of cholesterol to coprostanol has been measured in groups of healthy subjects before, during and after they received the antibiotics ampicillin, bacitracin, clindamycin, co‐trimoxazole, doxycycline, erythromycin, metronidazole, nalidixic acid, ofloxacin or vancomycin orally for 6 days. Before they received antibiotics, the subjects demonstrated two distinct patterns of cholesterol conversion. One pattern was characterised by extensive conversion of cholesterol, the other by little or no conversion. Intake of bacitracin, clindamycin, erythromycin, metronidazole and vancomycin significantly reduced the conversion to coprostanol. In the groups receiving ampicillin or doxycycline, marked reductions were found in most of the subjects. No alterations were found in the groups receiving co‐trimoxazole, nalidixic acid or ofloxacin. In 6 subjects no conversion of cholesterol to coprostanol was found up to 5 weeks after the end of the antibiotic intake. We conclude that orally given antibiotics may cause alterations in the intestinal conversion of cholesterol, reflecting changes in the anaerobiC., Gram‐positive component of the gut flora.

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