Serial Subcultivation of Giardia lamblia in Keister's Modified TYI-S-33 Medium Containing Ultroser G

ABSTRACT. The ability of Giardia strains of the duodenalis type to grow in Keister's modified TYI-S-33 medium varies with serum lot. Recently, strains of Giardia including MR4, WB, and Human-1-Portland, have been cultivated in Keister's modified TYI-S-33 medium containing the serum substitute Ultroser G and have been cultured serially at least 40 times. An optimal concentration of 8% Ultroser G promotes maximal growth in Keister's modified TYI-S-33 medium for all three strains. This concentration of Ultroser G will produce a two-log increase in the number of trophozoites in approximately three days post-inoculation. Generation times for the trophozoites ranging from 6 to 11 h have been achieved in Keister's modified TYI-S-33 containing 10% adult bovine serum and from 8 to 13 h in Keister's modified TYI-S-33 with 8% Ultroser G. Despite the excellent growth of Giardia strains in medium containing Ultroser G, the maximum trophozoite density is only about half of that achieved in Keister's modified TYI-S-33 medium supplemented with 10% adult bovine serum. Comparisons of trophozoites grown with serum or the serum substitute reveal no discernable differences in morphology and motility. Additionally, these strains have been successfully cryopreserved and revived in Keister's modified TYI-S-33 medium supplemented with Ultroser G. Because Ultroser G is a characterized mixture of six main groups of ingredients (growth factors, adhesion factors, mineral trace elements, hormones, binding proteins, and vitamins), the variability in cell proliferation that may occur when changing serum lots should be minimized when using this product.