An investigation into the pathogenic properties of Escherichia coli strains BLR, BL21, DH5 alpha and EQ1

Aims: To examine Escherichia coli strains EQ1, DH5 alpha, BLR and BL21 for known pathogenic mechanisms. Methods and Results: Using specific DNA probes, the strains were shown not to carry the genes encoding invasion, various adhesion phenotypes or expres sion of a range of enterotoxins. The strains were unable to express long-ch ain lipopolysaccharide and were susceptible to the effects of serum complem ent. Using a BALB/c mouse model, the strains were shown to be unable to sur vive in selected tissues or to persist in the mouse gut. Using a chick mode l, strains EQ1, BLR and BL21 invaded livers but not spleens; only strain EQ 1 persisted in the chick gut. In Merino sheep, only strain EQ1 was detected 6 d postinfection. Conclusions: Escherichia coli strains EQ1, DH5 alpha, BLR and BL21 did not carry the well-recognized pathogenic mechanisms required by strains of E. c oli causing the majority of enteric infections. Significance and Impact of the Study: Escherichia coli strains EQ1, DH5 alp ha, BLR and BL21 were considered to be non-pathogenic and unlikely to survi ve in host tissues and cause disease.