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United States Department of Agriculture

Agricultural Research Service

Title: Changes in the Microbial Ecology of a Mixed Anaerobic Bacterial Culture Challenged with Vancomycin

item Poole, Toni
item Stanker, Larry
item Nisbet, David

Submitted to: Miscellaneous Publishing Information Bulletin
Publication Type: Abstract Only
Publication Acceptance Date: September 21, 1999
Publication Date: N/A

Technical Abstract: 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 4 micrograms/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 daily by plating on M-Enterococcus medium. Prior to vancomycin treatment Enterococcus spp., and Pediococcus sp. were present in all three cultures at 10**8 and 10**4 CFU/ml, respectively. After two days of treatment, no Enterococcus spp. were isolated from culture A or B, however; pediococcus numbers increased to 10**7 CFU/ml in both cultures then declined to 10**6 CFU/ml after removal of antibiotic. On this dosing schedule vancomycin resistant enterococci did not emerge. Pediococcus has a naturally occurring resistance to vancomycin due to a unique cell wall precursor. Molecular analysis of the mixed culture before and after treatment with vancomycin indicated that no genes commonly associated with vancomycin resistance, VanA, VanB, VanC-1, VanC-2, VanD, VanR, or VanX, were present in the mixed culture.

Last Modified: 4/22/2015
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