EFFECT OF NORMAL INTESTINAL FLORA OF CHICKENS ON COLONIZATION BY VIRULENT COLICIN V-PRODUCING, AVIRULENT, AND MUTANT COLICIN V-PRODUCING AVIAN ESCHERICHIA-COLI

Colonization of the intestinal tracts of newly hatched chicks with Esc herichia coli was attempted by swabbing test organisms onto the air-sh ell of 19-day-old embryos. Test organisms consisted of two virulent E. coli isolates, one avirulent isolate, and one laboratory-derived muta nt of the avirulent isolate carrying a recombinant plasmid coding for Colicin V production. Chicks were cultured weekly for 3 weeks for tota l E. coli and for the test organisms using selective media. Control ch icks were sampled on weeks 1 and 5, and the normal E. coli intestinal microflora were examined for the production of colicins. The two virul ent E. coli isolates maintained colonization of the chicks for the 3-w eek test period, with titers decreasing from 10(1) to 10(2) colony-for ming units (CFU)/g of intestine. The avirulent isolate and laboratory mutant did not consistently colonize the intestinal tracts. The majori ty of intestinal samples taken from the control chicks at 1 and 5 week s had colicin-producing E. coli that were inhibitory to the test organ isms.