IDENTIFICATION OF PLASMID AND CHROMOSOMAL COPIES OF 987P PILUS GENES IN ENTEROTOXIGENIC ESCHERICHIA-COLI 987

A DNA probe derived from the subunit gene of a cloned 987P determinant was used to characterize the locations of the 987P genes in several E scherichia coli strains. We examined E. coli 987, a nonpiliated mutant of strain 987 (I36) that does not express 987P in vitro, and a varian t of I36 that expressed 987P following growth in vivo. We found that p lasmid and chromosomal copies of the 987P subunit gene could be differ entiated in strain 987 by restriction endonuclease analysis and Southe rn blot hybridization. The nonpiliated mutant I36 had lost the plasmid copy but retained the chromosomal copy of the 987P gene. A 987P-pilia ted variant of I36, which did not contain the 987P plasmid, colonized and caused diarrhea in neonatal pigs similarly to wild-type 987. The p lasmid that hybridized with the 987P probe was transferred from strain 987 to an E. coli K-12 strain by conjugation. We were unable to demon strate expression of 987P by these transconjugants. The data suggest t hat the chromosomal and plasmid copies of the 987P genes may interact to influence 987P expression.