Studies on the Ameba-Bacteria Relationship in Amebiasis

Comparative Results of the Intracecal Inoculation of Germfree, Monocontaminated, and Conventional Guinea Pigs with Entamoeba Histolytica

Summary and Conclusions

Germfree, monocontaminated, and conventional (control) guinea pigs were maintained on identical sterilized rations and inoculated intracecally with E. histolytica derived from cultures of the ameba with T. cruzi. The results showed that none of 35 germfree animals developed amebic lesions. Furthermore, the longest observed period of survival of the ameba in the germfree intestine was five days, in one animal, and the amebae were few in numbers and in poor condition when observed in animals sacrificed beyond the second post-inoculation day. Of 37 conventional guinea pigs inoculated as controls for the germfree series, 34 developed acute ulcerative amebiasis, and the other three animals harbored the ameba when sacrificed on the 21st post-inoculation day. The results of similar studies with monocontaminated animals were in great contrast to those obtained in the germfree series. Acute ulcerative amebiasis was produced in guinea pigs of two experimental series which harbored E. coli and A. aerogenes, respectively, as monocontaminants. The results have shown that although E. histolytica is unquestionably the causative organism of intestinal amebiasis, the responsibility for the disease must be shared with other microorganisms, the activities of which contribute to the etiology, pathogenesis, and pathology. In the absence of such microbial associates, the ameba appeared to be a harmless microbe incapable of independent survival in the intestine.

Author Notes

National Institutes of Health, National Microbiological Institute, Laboratory of Tropical Diseases, Bethesda, Maryland.

LOBUND Institute, University of Notre Dame, Notre Dame, Indiana.