Catalase-positive . Aerobic, facultatively anaerobic. Heat resistance: Usually destroyed in 30 minutes at 60° C, but certain heat-resistant strains may withstand this exposure (Ayers and Johnson, Jour. Agr. Res., 3, 1914, 401; Stark and Patterson, Jour. Dairy Sci., 19, 1936, 495). Growth requirements: Good growth on ordinary laboratory media. Optimum growth temperature, between 30° and 37° C. Growth takes place at 10° and 45° C. Gas produced from glucose at 45° to 46° C. Eijkmann test positive (Eijkmann, Cent. f. Bakt., I Abt., Orig., S7, 1904, 74; Perry and Hajna, Jour. Pact., 26, 1933, 419). Serology: A large number of serological types which seem to differ in pathogenic significance are included in this species as defined here. While it has long been known that E. coli is serologically heterogeneous, Kauffmann and his associates have brought some semblance of order to the mass of divergent types present in this species. Among significant contributions to the establishment of a scheme of serological classification, the following may be listed: Kauffmann (Acta. Path, et Microbiol. Scand., 20, 1942, 21; 21, 1944, 20; Jour. Immunol., 57, 1947, 71), Knipschildt (Un- dersogelser over Coligruppens Serologi. A. Busk, Copenhagen, 1945) and Vahlne (Serological typing of the colon bacteria. Gleerupska Univ. Bokhandeln, Lund, 1945). Like the salmonellas and shigellas, strains of E. coli are divided into groups on the basis of their heat-stable somatic (O) antigens. The O groups are subdivided on the basis of sheath, envelope or capsular (K) antigens, which have the property of inhibiting O agglutination just as the Vi antigen inhibits the O agglutination of Salmonella typhosa. The ability of these K antigens to inhibit O agglutination is an- nulled by heating, and they are divided into three categories (L, B, A) by their physical properties, particularly by the resistance to heat of their ability to inhibit O aggluti- nation and to bind their respective agglu- tinins. Finally, the organisms are divided into serotypes on the basis of their flagellar (H) antigens. To date, approximately 135 O groups, 75 K antigens and 40 H antigens have been recognized and characterized. Since these antigens may occur in different combinations, it is obvious that the number of serotj'pes existent within the species is much greater than the number recognized to date. Within recent years there has been a great increase in interest in the serology of E. coli due to ihe association of certain sero- types with severe outbreaks of infantile diarrhea. Among the earlier papers dealing with this problem are those of Bray (Jour. Path, and Pact., 57, 1945, 239), Bray and Beaven (Jour. Path, and Pact., 60, 1946, 395), Giles, Sangster and Smith (Arch. Dis. Childhood, 24, 1949, 45) and Kauffmann and Dupont (Acta Path, et Microbiol. Scand., 27, 1950, 552). Since these papers were published, the observations of the above- mentioned investigators have been con- firmed by a great number of workers in many different countries. While it is not yet clear how many different strains of E. coli may be involved in the etiology of infantile diarrhea, the following have been found repeatedly in association with the disease: 026:P6; 055: B5; 0111 :B4; 0127:B8; and 0128:B12. For a comprehensive summary of the association of E. coli serotypes with in- fantile diarrhea and other pathological conditions, see Kauffmann {Enterobac- teriaceae, 2nd edition, E. Munksgaard, Copenhagen, 1954). Comments : Many varieties of this species have been given specific or varietal names. The majorit.y of these varieties, a number of which are based on differences in sugar fermentations, are not now regarded as significant. Other varieties have been established on the basis of the production of a yellow pigment, a lack of motility, differ- ences in the appearance of colonial growth, a failure to coagulate milk, an inability to produce indole or on the basis of isolation from different regions of the intestine or other differences in habitat, etc. Source: Originally isolated by Escherich from the feces of breast-fed infants. Habitat: Found as a normal inhabitant of the intestines of mail and of other vertebrates. Widely distributed in nature. Frequently causes infections of the urogeni-
