[Selection of physiologic bacterial flora by chemotherapeutic agents]

A variety of antimicrobial agents has been shown to induce alterations in the bacterial homeostasis of the human microflora. Although the role of the normal flora is still poorly understood, there is evidence that alterations in the flora have a number of important clinical consequences. The normal flora acts as a natural defence against colonization or infection with pathogens. In addition, the altered flora may assume importance as a reservoir of potential pathogens. Thus, antibiotic-induced colonization predisposes patients to subsequent endogenous infections with these organisms which, in turn, have been rendered partially or totally resistant to formerly highly active agents. Broad spectrum antimicrobials with a high degree of biliary elimination show a marked impact on the faecal flora. Susceptible enteric bacteria are eliminated within 48 hours and are replaced by enterococci and Candida albicans. Recolonization occurs after discontinuation of therapy by multiresistant organisms like Klebsiella/Enterobacter and Pseudomonas. Oral antibiotics also lead to substantial alterations in the composition and resistance patterns of the faecal flora. In clinical medicine we should be aware of the substantial alterations of the human microflora which may accompany the use of antimicrobial agents.