Characterization of a human isolate of Tritrichomonas foetus (cattle/swine genotype) infected by a zoonotic opportunistic infection

Abstract

Tritrichomonas species flagellates (IMC strain) were isolated from the biliary tract of an individual who had developed cholecystitis as a complication of acquired agammaglobulinemia. Sequence analysis of Tritrichomonas sp. (IMC clone 2 (cl2)) was performed for several genetic regions including the ITS1-5.8S rDNA-ITS2 region, the cysteine protease (CP)-1, CP-2 and CP-4 to CP-9 genes, and the cytosolic malate dehydrogenase 1 gene. In addition to comparison of the variable-length DNA repeats in the isolate clone with those in T. foetus (Inui cl2) and the T. mobilensis (U.S.A.: M776 cl2) reference strains, this analysis showed that the Tritrichomonas sp. (IMC cl2) was T. foetus (cattle/swine genotype). Injection of T. foetus (IMC cl2) directly into the livers of CBA mice resulted in liver abscess formation on Day 7. Moreover, inoculation via orogastric intubation caused infection in the cecum on Day 5 in CBA mice co-infected with Entamoeba histolytica (HM-1: IMSS cl6). T. foetus (IMC cl2) was able to grow in YI-S medium for over 20 days, even at 5°C. These results indicate that the T. foetus isolate is able to survive in the feces and edible organ meat of the definitive host for a prolonged period of time, and it is possible that the parasite could infect humans.

Fig. 1.

Scanning electron microscopy images of three Tritrichomonas strains: IMC strain clone 2 [IMC cl2] [Tritrichomonas foetus (IMC cl2)] (A, B, C) and Tritrichomonas mobilensis (U.S.A.: M776 cl2) (D, E, F). A and D: organisms in interphase. B and E: organisms in pre-binary division phase. C and F: organisms under low magnification.

Fig. 2.

Comparison of the cysteine protease 2 gene sequences Tritrichomonas foetus (IMC cl2) and the five Tritrichomonas spp. reference strains.

Fig. 3.

Comparison of variable-length DNA repeats using the TR7/TR8 primers. Lane 1: Tritrichomonas foetus (IMC cl1); Lane 2: T. foetus (IMC cl2); Lane 3: T. foetus (Inui cl1); Lane 4: T. foetus (Inui cl2); Lane 5: Tritrichomonas mobilensis (M776 cl1); Lane 6: T. mobilensis (M776 cl2); Lane 7: Trichomonas vaginalis; Lane 8: Pentatrichomonas hominis.

Fig. 4.

Sequence alignment of the TR7/TR8-amplified variable-length repeats of Tritrichomonas foetus (IMC cl2), Tritrichomonas foetus (Inui cl2) and Tritrichomonas mobilensis (M776 cl2).

Fig. 5.

Growth kinetics of Tritrichomonas foetus (IMC cl2), Tritrichomonas foetus (Inui cl2) and Tritrichomonas mobilensis (M776 cl2) at 5°, 18°, 25° and 35.5°C. The mean numbers and standard deviations of duplicate cultures are plotted. T. foetus (IMC cl2): ●–●, T. foetus (Inui cl2): ∆–∆, T. mobilensis (M776 cl2): □–□.

Fig. 6.

Thin sections of liver abscesses from CBA mice infected with Tritrichomonas foetus (IMC cl2) 7 days after inoculation (periodic acid–Schiff (PAS) staining) (A, B). Thin sections of the cecum of CBA mice co-infected with T. foetus (IMC cl2) and Entamoeba histolytica (HM-1:IMSS cl6). Data obtained at 5 days after inoculation via orogastric intubation are shown (PAS staining) (C, D). Black arrows: T. foetus (IMC cl2), white arrows: E. histolytica (HM-1:IMSS cl6).