Two recent developments have stimulated renewed interest in E, scherichia coli infections of man. In the first place, through the important investigations of Kauffmann and his associates (1, 2) extensive knowledge has been gained on the antigenic pattern of this species. The discovery by Kauffmann of antigens as inhibitors of O agglutinability and the identification of the various antigens (the somatic O antigens, the envelope or surface L and B antigens, the capsular A antigens, and the flagellar H antigens) have brought order to the serological grouping and typing of E. coli and made possible studies on the relationship between antigenic types of E. coli and various infections.The second discovery of major importance is the finding of the association of two serological groups of E. coli, namely, serogroups O l l l and 055, with epidemic and sporadic diarrheal disease of infants. In 1923 and 1927, Adam (3, 4) reported on the recovery of several biochemical types of E. coli from patients with diarrheal disease. It remained for the British investigators Bray (5), Bray and Beavan (6), Giles and Sangster (7), Giles, Sangster, and Smith (8), Smith (9), as well as Taylor, Powell, and Wright (10) to establish the fact that in certain outbreaks of epidemic diarrhea two serogroups of E. coli are found in a high percentage of affected children and 0nly rarely in healthy infants, children, and adults. These two antigenic groups have been identified as serogroups O l l l and 055. The observations of these investigators have been confirmed and extended in various parts of the world, including the Scandinavian countries by Kauffmann and Dupont (11), the Netherlands by Beeuwkes, Hodenpijl, and ten Seldam (12), Germany by Braun (13), and the United States by Modica, Ferguson, and Ducey (14), Neter and Shumway (15), Neter and Webb (16), Neter, Webb, Shumway, and Murdock (17). Very recently, Orskov (18) reported on the occurrence of E. coli belonging to O-group 26 in cases of infantile diarrhea and in white scours of newborn calves. Thus it appears likely that groups other than O l l l and 055 may be associated with diarrheal disease of infants.

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Summary The effects of lecithin and cholesterol on Escherichia coli O26 hemagglutination and hemolysis were studied and the following results obtained. Both crude and purified lecithin preparations, after contact with the bacterial antigen, inhibited E. coli hemagglutination. As little as 0.5 mg (0.1 mg per ml) of the purified preparation E prevented this reaction completely. This preparation also inhibited E. coli hemolysis. Cholesterol in amount of 0.05 mg, after contact with the bacterial antigen, inhibited E. coli hemagglutination and 0.5 mg prevented hemolysis. The inhibitory effect of both lecithin and cholesterol depends, aside from their concentration, upon the amount of bacterial antigen used, the length of time of contact between inhibitor and antigen and the temperature at which the mixtures were kept. Purified lecithin preparation E and cholesterol, when allowed to act on red blood cells, did not inhibit hemagglutination, indicating that their major effect is upon the antigen. Red blood cells treated with inhibitor-antigen mixtures failed to adsorb homologous bacterial antibodies of human origin, as evidenced by failure to be agglutinated by anti-human globulin (rabbit) antiserum; the latter serum caused agglutination of erythrocytes which had been modified by antigen alone and then treated with the same bacterial antiserum. Cholesterol-antigen mixture was precipitated at least as well as the untreated antigen by homologous E. coli antiserum and lecithin-antigen mixtures but slightly less than the control antigen, indicating that the inhibitory effects of the lipids on E. coli hemagglutination is not due to destruction of the bacterial antigen. The phenomena of bacterial (Escherichia coli) hemagglutination and hemolysis and their inhibition by lecithin and cholesterol are discussed.