The influence of third-generation cephalosporins on the aerobic intestinal flora.

The influence of three third-generation cephalosporins with varying degrees of biliary excretion on the aerobic flora was investigated. The faecal flora prior to therapy with one of these substances consisted mainly of anaerobic bacilli. Escherichia coli was present in concentrations of 10(9) organisms/g stool. Candida albicans and enterococci were observed in concentrations of 10(5) - 10(6) organisms/g stool. Within 24 hours after the administration of ceftriaxone and cefoperazone, the gram-negative aerobic flora was completely eradicated. C. albicans and enterococci increased to 10(9) organisms/g stool. Between the third and tenth days (mean 6.7 days) of therapy Pseudomonas aeruginosa, Enterobacter and Citrobacter in this order of frequency reappeared in the faecal flora with complete resistance to all betalactam antibiotics. C. albicans and enterococci decreased to 10(7) organisms/g stool. The anaerobic flora was largely unaltered. In contrast, cefotaxime had only a moderate influence on the aerobic faecal flora. Concentrations of gram-negative organisms decreased to 5 X 10(7) organisms/g stool during the first five days of therapy; the concomitant increase in C. albicans and enterococci was approximately 1 log 10. No alterations in the susceptibility pattern were observed. We would like to emphasize that substantial alterations of the faecal flora and the susceptibility pattern of antibiotics may accompany the use of antimicrobial agents, particularly those with a high degree of biliary elimination.