ENTEROPATHOGENIC ESCHERICHIA COLI SEROTYPES

Investigations in the past have made i t clear that diarrheal diseases of infants may be caused by a variety of microorganisms. Epidemics and sporadic cases of infantile diarrhea or diarrhea of the newborn may be caused by agents such as Salmonella or Shigella. Occasionally, a bacterium of another group is thought to be the etiological agent in a particular outbreak and, in certain instances, viral agents have been incriminated. In a large number of otherwise unexplained epidemics of diarrheal disease of infants, however, certain Escherichia coli serotypes are recovered. The designation enteropathogenic E. coli has been suggested for these particular serotypes. The concept that certain E. coli types might be involved in infantile diarrhea is not a new one. For more than 50 years workers have investigated and discussed the role of coliform bacteria in summer diarrhea, infantile enteritis, or diarrhea of the newborn (see Dupontl for references to earlier literature). Unfortunately, most of the earlier investigators were hampered by the fact that they used only biochemical tests in their attempts to differentiate between the suspected E. coli cultures isolated from cases and those recovered from normal infants or adults. By themselves, biochemical methods are inadequate for such differentiation because the E. coli group is composed of many different serotypes that often give identical biochemical reactions. A few workers used serological methods, however, in addition to biochemical tests. In fact, Goldschmidt2 employed a slide agglutination technique to differentiate “Dyspepsiekoli” cultures from cases of infantile diarrhea and to trace the epidemic spread of the bacteria in the investigation of an institutional outbreak. As pointed out by Dupont,‘ it is unfortunate and strange that Goldschmidt’s work did not receive the attention it deserved. Also, Dulaney and Michelsod utilized serologic methods to demonstrate the relationship of a number of strains of Bacterium coli mutabile which they isolated from cases of infantile diarrhea during an epidemic. Recently, it has been learned that the cultures isolated by Dulaney and Michelson belong to E. coli 0 group 18a, 18c. The family Enterobacteriaceae is composed of several groups of bacteria such as the Salmonella group, the Shigella group, and the Escherichia coli group. Each of these groups is made up of biochemically similar microorganisms, and the groups correspond to genera in greater or lesser degree. It should be emphasized that while types within a group cannot be differentiated by biochemical tests, the biochemical reactions given by a culture are used to determine the group of Enterobacteriaceae to which it belongs. Serologic methods must then be employed to determine the serotype within a biochemical group. The work of Kauffmann4-’ and his collaborators made possible the development of a system for serologic typing of E. coli cultures and resulted in an antigenic schema in which the microorganisms may be classified. Interest in members of the E. coli group has been stimulated by the association