Transfer Factors in Escherichia coli with Particular Regard to Their Incidence in Enteropathogenic Strains

SUMMARY: Strains of Escherichia coli were isolated whose resistance to ampicillin (Ap), tetracyclines (Tc) or streptomycin and sulphonamides (SmSu) or whose production of colicine (Col) or α-haemolysin (Hly) could not be transmitted to E. coli k 12 F−. Determinants controlling these characters (except Ap), could be mobilized in some of them after infection with transfer factors. Of 60 strains of E. coli isolated from the faeces of healthy pigs, cattle and human beings and selected because they did not possess R factors and did not produce colicine, α-haemolysin, porcine enterotoxin (Ent) or K 88 antigen (transmissible characteristics), 20 (33%) contained transfer factors that could mobilize determinants from one or more of nine determinant donor strains; 8 contained at least two transfer factors, one fi − and the other fi +. The nine determinant donor strains contained Tc, SmSu, Col or Hly determinants; some were wild strains and others were obtained from interrupted mating experiments in which E. coli k 12 F− was the recipient strain. The ability of a transfer factor to mobilize a determinant was not simply a function of the transfer factor and the determinant but was strain-dependent. Positive results were obtained most frequently when transfer was between strains of k 12. Transfer factors that could mobilize determinants in determinant donor strains were found in all except one of 78 porcine enterotoxigenic strains of E. coli selected because they did not possess R factors or transmissible colicine. Nearly all of them produced α-haemolysin and over half of them K 88 antigen. On the evidence available, the high incidence of transfer factors in these strains suggests that enterotoxin production in all of them was controlled by transmissible plasmids and that the genetic determinants controlling α-haemolysin production in some of them might be chromosomal. The linkage between Ent and the factor responsible for its transfer was not always close. Despite a previous statement to the contrary (Smith & Halls, 1968), this transfer factor was fi − both fi − and fi + factors could transfer Hly. No close association between the plasmids controlling the five characteristics Neo (neomycin resistance), Ent, Col, Hly and K 88 was apparent in mating experiments using as donor a porcine strain of E. coli carrying all five transmissible plasmids. Transfer factors were found in 15 of 21 human enteropathogenic strains and in one of five sheep enteropathogenic strains; none of these 26 strains possessed characteristics known to be transmissible.