Cysteine protease activity of feline Tritrichomonas foetus promotes adhesion-dependent cytotoxicity to intestinal epithelial cells.

Trichomonads are obligate protozoan parasites most renowned as venereal pathogens of the reproductive tract of humans and cattle. Recently, a trichomonad highly similar to bovine venereal Tritrichomonas foetus but having a unique tropism for the intestinal tract was recognized as a significant cause of colitis in domestic cats. Despite a high prevalence, worldwide distribution, and lack of consistently effective drugs for treatment of the infection, the cellular mechanisms of T. foetus pathogenicity in the intestinal tract have not been examined. The aims of this study were to determine the pathogenic effect of feline T. foetus on porcine intestinal epithelial cells, the dependence of T. foetus pathogenicity on adhesion of T. foetus to the intestinal epithelium, and the identity of mediators responsible for these effects. Using an in vitro coculture approach to model feline T. foetus infection of the intestinal epithelium, these studies demonstrate that T. foetus promotes a direct contact-dependent activation of intestinal epithelial cell apoptosis signaling and progressive monolayer destruction. Moreover, these pathological effects were demonstrated to be largely dependent on T. foetus cell-associated cysteine protease activity. Finally, T. foetus cysteine proteases were identified as enabling cytopathic effects by promoting adhesion of T. foetus to the intestinal epithelium. The present studies are the first to examine the cellular mechanisms of pathogenicity of T. foetus toward the intestinal epithelium and support further investigation of the cysteine proteases as virulence factors in vivo and as potential therapeutic targets for ameliorating the pathological effects of intestinal trichomonosis.

Feline Tritrichomonas foetus adhere to intestinal epithelium by receptor-ligand-dependent mechanisms.

Tritrichomonas foetus (TF) is a protozoan that infects the feline ileum and colon resulting in chronic diarrhea. Up to 30% of young purebred cats are infected with TF and the infection is recognized as pandemic. Only a single drug, characterized by a narrow margin of safety and emerging development of resistance, is effective for treatment. While the venereal pathogenicity of bovine TF is attributed to adherence to uterovaginal epithelium, the pathogenesis of diarrhea in feline TF infection is unknown. The aim of this study was to establish an in vitro model of feline TF adhesion to intestinal epithelium. Confluent monolayers of porcine intestinal epithelial cells (IPEC-J2) were infected with axenic cultures of feline TF that were labeled with [(3)H] thymidine or CFSE and harvested at log-phase. The effect of multiplicity and duration of infection, viability of TF, binding competition, formalin fixation and cytoskeletal inhibitors on adherence of feline TF to IPEC-J2 monolayers was quantified by liquid scintillation counting and immunofluorescence. [(3)H] thymidine and CFSE-labeled TF reproducibly adhered to IPEC-J2 monolayers. Clinical isolates of feline TF adhered to the intestinal epithelium in significantly greater numbers than Pentatrichomonas hominis, the latter of which is a presumably nonpathogenic trichomonad. Adhesion of TF required viable trophozoites but was independent of cytoskeletal activity. Based on saturation and competition binding experiments, adherence of feline TF to the epithelium occurred via specific receptor-ligand interactions. The developed model provides a valuable resource for assessing pathogenic mechanisms of feline TF and developing novel pharmacologic therapies for blocking the adhesion of feline TF to the intestinal epithelium.

Documentation of in vivo and in vitro aerobic resistance of feline Tritrichomonas foetus isolates to ronidazole.

BACKGROUND: The mainstays of treatment for clinically important trichomonad infections are the 5-nitroimidazoles. Metronidazole resistance of feline Tritrichomonas foetus is presumed because of common treatment failure, and tinidazole does not consistently eradicate infection. To date, ronidazole is the only drug demonstrated as effective for treatment of cats infected with T. foetus. OBJECTIVE: To document in vivo treatment failure and identify underlying causes and in vitro conditions of resistance of feline T. foetus to ronidazole. ANIMALS: Two intact male Abyssinians failing>or=5 courses of treatment with increasing doses of 5-nitroimidazole drugs. An intact male Abyssinian documented to clear infection after treatment with a single course of ronidazole. METHODS: T. foetus isolates were cultured from feces and tested in vitro for susceptibility to ronidazole under aerobic and anaerobic culture conditions. A urogenital nidus of T. foetus infection was investigated by culture, polymerase chain reaction, or immunohistochemical testing of urogenital specimens. RESULTS: Resistance to ronidazole under aerobic conditions was uniquely identified in T. foetus isolated from cats with well-documented treatment failure. Treatment failure could not be attributed to reinfection, inappropriate treatment protocol, or presence of a urogenital nidus of infection. CONCLUSIONS AND CLINICAL IMPORTANCE: Clinical resistance to metronidazole, low efficacy of tinidazole, and present documentation of in vivo and in vitro resistance to ronidazole in some cats are consistent with a high level of cross resistance of feline T. foetus to 5-nitroimidazole drugs. Current lack of alternative drugs with clinical efficacy against feline T. foetus suggests that active investigation of other treatment approaches is warranted.