Antianaerobic antibiotic therapy promotes overgrowth of antibiotic-resistant, gram-negative bacilli and vancomycin-resistant enterococci in the stool of colonized patients

Infect Control Hosp Epidemiol. 2003 Sep;24(9):644-9. doi: 10.1086/502267.


Background and objective: Antianaerobic antibiotic therapy promotes persistent high-density growth of vancomycin-resistant enterococci (VRE) in the stool of colonized patients. We tested the hypothesis that antibiotic regimens with potent antianaerobic activity promote overgrowth of coexisting antibiotic-resistant, gram-negative bacilli in the stool of VRE-colonized patients.

Design: Eight-month prospective study examining the effect of antibiotic therapy on the stool density of gram-negative bacilli resistant to ceftazidime, ciprofloxacin, or piperacillin/tazobactam.

Setting: A Department of Veterans Affairs medical center including an acute care hospital and nursing home.

Patients: All VRE-colonized patients with at least 3 stool samples available for analysis.

Results: One-hundred forty stool samples were obtained from 37 study patients. Forty-nine (61%) of 80 stool samples obtained during therapy with an antianaerobic regimen were positive for an antibiotic-resistant, gram-negative bacillus, where-as only 14 (23%) of 60 samples obtained 4 or more weeks after completion of such therapy were positive (P < .001). Twenty-four (65%) of the 37 patients had one or more stool cultures positive for a gram-negative bacillus resistant to ciprofloxacin, ceftazidime, or piperacillin/tazobactam. The density of these organisms was higher during therapy with antianaerobic regimens than in the absence of such therapy for at least 2 weeks (mean +/- standard deviation, 5.6 +/- 1.4 and 3.9 +/- 0.71 log10 organisms/g; P < .001).

Conclusion: Limiting the use of antianaerobic antibiotics in VRE-colonized patients may reduce the density of colonization with coexisting antibiotic-resistant, gram-negative bacilli.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Anti-Bacterial Agents / therapeutic use*
  • Bacteria, Anaerobic / drug effects*
  • Drug Resistance, Bacterial
  • Enterococcus / drug effects*
  • Enterococcus / physiology
  • Feces / microbiology
  • Female
  • Gram-Negative Bacteria / drug effects*
  • Gram-Negative Bacteria / pathogenicity
  • Humans
  • Male
  • Middle Aged
  • Population Dynamics
  • Prospective Studies
  • Vancomycin Resistance*


  • Anti-Bacterial Agents