Effect of broad-spectrum parenteral antibiotics on "colonization resistance" of intestinal microflora of humans

Abstract

Studies with animals have shown that the normal intestinal microflora protects against colonization by new strains ("colonization resistance") and that this protective effect may be related to the anaerobic component of the microflora. However, colonization resistance has not been shown in humans. We administered cefoxitin, piperacillin, cefoperazone, and aztreonam intravenously to healthy subjects for 9 days and monitored the acquisition of new isolates in the fecal flora. Seven of sixteen antibiotic-treated subjects but none of four untreated controls became colonized by gram-negative bacilli. However, there was no correlation between colonization and the particular drug given or the extent of suppression of anaerobes or of any other component of the fecal microflora. Cefoxitin and piperacillin were associated with the greatest increases in the numbers of drug-resistant bacteria and in fecal beta-lactamase content. The results of this study support the concept that colonization resistance occurs in humans and is diminished by antibiotic administration but fail to support the hypothesis that resistance is related to the anaerobic microflora.

Modulation of the intestinal flora of mice by treatment with aztreonam and tigemonam

“…Several studies have shown that oral or parenteral treatment with aztreonam in humans causes a pronounced decrease in the number of aerobic gram-negative rods without altering the composition of the anaerobic fecal flora (1,4,5,7,9,11,13). These results are explained by the intrinsic resistance of anaerobic bacteria to aztreonam.…”

Colonization resistance

“…In humans, a dramatic cure was reported in patients suffering from pseudomembranous colitis when fresh fecal suspensions were administered by an intrajejunal tube (9) or by enemas (9,41,46 (18). However, complete suppression of Shigella strains by E. coli was observed when the two organisms were introduced as the only flora in antibiotic-treated animals (20 (5). However, the concentration of cefoperazone in feces was more than 100-fold greater than the MICs for the challenge strains.…”

Carica papaya seed macerate as inhibitor of conjugative R plasmid transfer from Salmonella typhimurium to Escherichia coli in vitro and in the digestive tract of gnotobiotic mice

“…When plasmid transfer occurs in the digestive tract, the resulting transconjugants are generally unable to become established in that indigenous bacterial community (Duval-Iflah et al, 1994). By contrast, the spreading of plasmids which encode resistance to clinically important antibiotics in pathogenic bacteria has been observed often during antimicrobial therapy, which is believed to modify the normal microbiota and to lower host resistance against colonization by pathogenic plasmid-bearing bacteria (Barza et al, 1987). In addition, it should be pointed out that there were R plasmids encoding, simultaneously, resistance, virulence and other features (Sant'Ana et al, 1995).…”