APPROVED:

Abstract

for privacy Abstract approved: (----t-cr Dr. Lyle R. Brown R+ organisms isolated from fecal samples from swine contained various combinations of the following r determinants: tetracycline, kanamycin, streptomycin, ampicillin, and carbenicillin. Of the R+ isolates identified, over 90 % were grouped into several distinct Escherichia coli biotypes; R+ Klebsiella, Salmonella and Proteus were also encountered. Unique combinations of r deter-minants were found in association with specific E. coli biotypes, and one R factor, (Tc, Amp), showed predominance in some samples taken immediately postweaning. Identification of several isolates carrying this R factor implicated one biotype of E. coli, (380). R factor transfer through conjugation was tested into several recipients, including E. coli, Klebsiella, Salmonella enteriditis, and-8-1Proteus vulgaris, and frequencies ranging from 10 to 10 were observed. Higher frequencies of transfer were noted into homolgous species. Compatibility tests and acridine elimination experiments were performed on a selected number of R+ isolates