Effect of Vancomycin on Intestinal Flora of Patients Who Previously Received Antimicrobial Therapy

To evaluate the ecological disturbances of peroral vancomycin administration following cephalosporin administration, 20 healthy volunteers received cefuroxime axetil tablets (250 mg) perorally twice a day for 1 week, and 10 of these volunteers subsequently received vancomycin capsules (125 mg) perorally four times daily for 7 days. The concentration of vancomycin in feces after 1 week of vancomycin administration was high (mean +/- SD, 520 +/- 197 mg/kg), which correlated with the ecological disturbances noted in the vancomycin recipients. Vancomycin administration resulted in a rapid decrease in the numbers of intestinal Enterococcus faecium, Enterococcus faecalis, and Enterococcus durans (P < or = .05), while there was a significant emergence of motile enterococci with decreased susceptibility to vancomycin (Enterococcus gallinarum and Enterococcus casseliflavus; minimum inhibitory concentration, 4-16 mg/L) (P < or = .01). Because of vancomycin administration, there was also a significant overgrowth of vancomycin-resistant Pediococcus species and lactobacilli as well as of Klebsiella species, Citrobacter species, and Enterobacter species (P < or = .01). The numbers of bifidobacteria and Bacteroides species were significantly reduced during vancomycin administration. None of the enterococcal strains carried vanA or vanB. Twenty-two of the 27 motile enterococci carried the vanC-1 gene specific for E. gallinarum, whereas five strains carried the vanC-2(C-3) gene, thus implicating that they were E. casseliflavus or Enterococcus flavescens.