Deoxyribonucleic acid fragments of the naturally occurring conjugative K99 plasmid were cloned into vectors pBR322 and pBR325. The smallest deoxyribonucleic acid segment obtained that still expressed K99 was 4.5 megadaltons in size. With regard to the serological, adhesive, and morphological properties, no differences in the nature of the K99 antigen was observed between Escherichia coli strains carrying recombinant plasmids and those carrying pRI9901. Furthermore, the regulation of K99 expression from the recombinant plasmid deoxyribonucleic acid was similar to that from pRI9901. the low level of K99 expression in E. coli K-12 compared with natural K99-producing isolates seems to be host specific.
Animals Antigens, Bacterial