Infectivity and Recovery of Tetrahymena pyriformis Strain S from Adult Female Cockroaches (Periplaneta americana)*

Hemocoelomic injection of 5,800–8,000 cells of Tetrahymena pyriformis strain S per female cockroach resulted in lethargy of the insects within 24 hr and death within 72 hr. Ciliates could be recovered 24–48 hr after injection of these amounts of ciliates. Inoculation of smaller numbers of cells resulted in no apparent ill effects to the insects and ciliates could not be recovered.

After recovery from cockroaches and reestablishment in axenic culture, the ciliates were rounded and contained large numbers of lipid droplets which decreased on continued cultivation. The ciliates underwent a sequence of morphologic alterations involving a decrease in length and width to form ovoid cells, an approach to the pyriform shapes (but smaller than normal size), an elongation to an abnormal length/width ratio, and then, after 6 days in culture, a return to the normal shape with usual dimensions.