Effects of Imipenem-Cilastatin, Ertapenem, Piperacillin-Tazobactam, and Ceftriaxone Treatments on Persistence of Intestinal Colonization by

Antibiotics that are excreted into the intestinal tract may promote colonization by antibiotic-resistant pathogens due to the disruption of indigenous microflora (2). However, such antibiotics may also have a protective effect if they inhibit the growth of pathogens (2, 6). For example, ceftriaxone, piperacil-lin-tazobactam, and ertapenem did not promote the establish-ment of colonization by a strain of extended-spectrum--lactamase (ESBL)-producing Klebsiella pneumoniae during treatment in mice (MICs for the test strains were 4, 4, and 0.25 g/ml, respectively) (6). In similar experiments, pip-eracillin-tazobactam inhibited the establishment of coloniza-tion by vancomycin-resistant enterococci during treatment (the FIG. 1. Effect of subcutaneous antibiotic treatment on persistence of colonization with ESBL-producing Klebsiella pneumoniae strains P62 (A) and P10045 (B) in mice. High-density colonization was established by administering 106 CFU of the test strains by orogastric gavage in conjunction with subcutaneous clindamycin for 3 days. Two days after discontinuation of clindamycin (day 0), mice received subcutaneous antibiotic treatment once daily for 9 days. If the pathogens were not detected in stool, the lower limit of detection (2 log10 CFU/g) was assigned. Error bars indicate standard errors