Enterococci are present in the healthy gastrointestinal tract of humans and animals; however, they have recently become a public health concern due to their ability to acquire resistance to vancomycin. An anaerobic continuous-flow (CF) culture, of chicken gastrointestinal microflora containing 3 different enterococci species, was used to investigate the effect of vancomycin on the avian gastrointestinal microbial ecology. Three identical CF cultures were used. Culture A was treated with a continuous dose of 4µg/ml vancomycin for seven days followed with no vancomycin treatment for seven days. Culture B was treated as culture A, but given two rounds of treatment. Culture C was untreated. Enterococci were monitored by plating on M-Enterococcus medium. Prior to vancomycin treatment Enterococcus spp. and Pediococcus sp. were present in all three cultures at 108 and 104 CFU/ml, respectively. After two days of treatment, no Enterococcus spp. were isolated from culture A or B; however, pediococcus numbers increased to 107 CFU/ml in both cultures then declined to 106 CFU/ml after removal of antibiotic. On this dosing schedule vancomycin resistant enterococci did not emerge. Molecular analysis of each culture before and after treatment with vancomycin indicated that no genes commonly associated with vancomycin resistance, vanA, vanB, vanC, vanD, vanR or vanX were present. Pediococcus has intrinsic resistance to vancomycin due to a cell wall precursor different than those involved in vanA, vanB, vanC, or vanD phenotypes.