ABSTRACT
A nonsurgical rabbit model of enteric Shigella infection was developed for studying the pathogenesis and immunology of shigellosis and for evaluating Shigella vaccine candidates. In this model, rabbits are made susceptible to Shigella infection by a pre-inoculation conditioning procedure consisting of a 36-h nonfeeding period, with 250 mg of tetracycline administered in 250 ml of drinking water, 75 mg of cimetidine given intravenously, and two 15-ml doses of 5% sodium bicarbonate given orally immediately before orogastric administration of the bacterial inoculum. Lastly 2 ml of tincture of opium is administered intraperitoneally. With a virulent strain, Shigella flexneri 2a, the clinical and pathologic characteristics of shigellosis in this rabbit model were studied. Twenty hours after oral inoculation of 10(10) bacteria, all six experimental rabbits developed diarrhea and were lethargic or moribund, whereas the four control rabbits inoculated with sterile broth remained healthy. Histologic examination revealed severe, diffuse, necrotizing ileitis with hemorrhage in experimental rabbits, whereas no lesions were found in the controls. Although the major site of necrosis in this rabbit model was the ileum, as opposed to the colon in humans and nonhuman primates, the histologic morphology of the lesion was the same in the various hosts. Because it is relatively inexpensive and convenient, this model should facilitate study of the pathophysiology and immunology of shigellosis, thereby speeding development of oral vaccines, which can be tested in this animal model.
Subject(s)
Disease Models, Animal , Dysentery, Bacillary/pathology , Shigella flexneri , Animals , Dysentery, Bacillary/microbiology , Feces/microbiology , Female , Hemorrhage/pathology , Ileum/pathology , Male , Necrosis/pathology , Rabbits , Shigella flexneri/isolation & purificationABSTRACT
An enteropathogenic Enterococcus-like agent was isolated from a spontaneous outbreak of diarrhea that occurred in a colony containing neonatal rats. Diarrhea was experimentally reproduced in virus-antibody-free neonatal rats inoculated with this purified "enterococcus." Gram-positive cocci were adhered to the small intestinal villi of affected animals from which the organism was reisolated. The isolate's classification in the genus Enterococcus was confirmed by genetic probe; however, because of its unique fermentation pattern, it could not be definitively speciated. Indirect immunofluorescence assays indicate that this strain of enterococcus and Enterococcus hirae, another strain pathogenic for neonatal rats, differ antigenically. Enterococci should be considered as potential etiologic agents in outbreaks of diarrhea involving neonatal rats and future efforts directed to increasing our understanding of the pathophysiology of this disease.
Subject(s)
Animals, Newborn/microbiology , Diarrhea/veterinary , Enterococcus/growth & development , Gram-Positive Bacterial Infections/veterinary , Rats/microbiology , Rodent Diseases/microbiology , Animals , Diarrhea/microbiology , Diarrhea/pathology , Enterococcus/isolation & purification , Fluorescent Antibody Technique/veterinary , Gram-Positive Bacterial Infections/pathology , Rodent Diseases/pathologyABSTRACT
A Lancefield group D enteric streptococcus was isolated from diarrheic suckling rats that had been inoculated orally with stool from a diarrheic human. After oral administration of the organism to other suckling rats, diarrhea was reproduced, and the enteric streptococcus was reisolated. The brush border of small intestinal villi in affected animals was coated with numerous adherent gram-positive cocci. The organism was identified as Enterococcus hirae by a battery of biochemical tests. These and previous studies indicate that certain enterococci should be considered as etiologic agents of diarrheal disease in neonatal animals.
