Differences in Culturability, Infectivity and Pathogenicity of Human Strains of Endamoeba histolytica.

Abstract

Summary Investigations have been undertaken in an attempt to reconcile some of the many conflicting opinions which have developed regarding the pathogenicity of E. histolytica. The problem undertaken and presented in this communication concerns the culturability, infectivity and pathogenicity of 18 different “strains” of the organism, obtained from persons in New Orleans. The hosts varied in age from 2 to 59 years. All but one were hospital or clinic patients, the majority of whom complained of some type of colitis. In 11 cases stools containing cysts or trophozoites were obtained; in 5 cases proctoscopic material was utilized, in one case a purgative specimen was secured and in one instance the inoculum consisted of material previously cultured in a hospital laboratory. For culture work a solid egg-slant base was employed, with a liquid overlay of physiological salt solution containing 0.5% crude liver extract and special rice starch. Cysts were concentrated and washed before seeding the cultures; trophozoites in fecal or mucous samples were placed directly in the culture tubes. Kittens served as the principal animals to test infectivity and pathogenicity of each strain. A minimum of 5 kittens was employed. Pathogenicity was first estimated on the basis of clinical evidence, then carefully studied at autopsy. The length of intestine from the posterior level of the ileum through the rectum was considered as 8 separate segments and amebic invasion of the bowel separately assessed for each segment. Four degrees of pathogenicity were recognized and were designated as +, ++, +++ and ++++. Based on these symbols a pathogenic index was developed to afford comparisons between different series. Of the 18 “strains” 6 proved difficult to grow in culture; 4 of these were unsatisfactory for animal work and were discarded.