DESCRIPTION OF A BLASTOCYSTIS SPECIES FROM RATTUS-NORVEGICUS

Two isolates (WR1 and WR2) of Blastocystis from laboratory-bred Wistar rats were axenized by a method of colony growth in soft agar combined with antibiotic treatment. The colonies were cultured in Iscove's mod ified Dulbecco's medium (IMDM) and Bacto agar mixture supplemented wit h 10% horse serum in the presence of thioglycollate. The cells from th e colonies had an ameboid outline with a central body. Large inclusion s were seen in the central body of some cells. Some granular forms wer e also found. In the axenic culture of isolate WR2, about one-third of the organisms were granular forms. Cysts were found in the axenic cul ture of both isolates. This is the first report of such cyst formation in in vitro culture. The karyotypic patterns of both isolates of the rat Blastocystis were analyzed by pulsed-field gel electrophoresis (PF GE). A total of 13 chromosomal bands were separated, ranging from 1.86 Mb to 295 kb. The karyotypic patterns of the rat Blastocystis were di fferent from those of B. hominis and reptilian Blastocystis. On the ba sis of the above-mentioned differences, the rat Blastocystis is assign ed as B. ratti sp. nov.