Comparative study of the morphology and sensitivity to damaging factors of capsular and acapsular variants of Escherichia coli CA 189

E. coli strain SA 189 has been isolated from a calf with E. coli infection. The cultivation of this strain on a solid culture medium has resulted in its dissociation into two variants due to the loss of the capsule by the cells of the initial culture. Both variants of E. coli strain SA 189 (capsular and acapsular) are equally sensitive to antibiotics. The capsular variant has a narrower range of sensitivity of colicins and shows greater resistance to the bactericidal action of normal blood serum than the acapsular one. Bacteria belonging to these two variants differ perceptibly in the kinetics of disturbances in the barrier properties of their membrane apparatus under the action of cetyltrimethylammonium bromide, a cation detergent. The conditions permitting the differentiation of the capsular and acapsular forms of E. coli strain SA 189 by the kinetics of the damaging action of this detergent have been experimentally selected.