Success in the toxoplasma dye test

Objectives: To compare the success rate of the toxoplasma dye test using di fferent accessory factors (human serum as a source of complement) and diffe rent batches of tachyzoites produced in vivo and in vitro. Methods: Twenty-five accessory factors were used in the dye test to assess both types of tachyzoite. Batches of tachyzoites were produced in vivo (n = 49) and in vitro (n = 23) and their performance assessed against panels of accessory factors. Performance was recorded as success or failure (incorre ct results, total killing or no killing). Results: With in vivo tachyzoites 21/25 accessory factors were successful i n greater than or equal to1 dye test runs, whereas with in vitro tachyzoite s all 25 were successful. One or more failure was recorded for 19/25 and 12 /25 accessory factors using in ville and in vitro tachyzoites, respectively (P < 0.05). The number of successful dye test runs was less for in vivo (9 2/141, 65%) than in vitro (140/163, 86%) tachyzoites (P < 0.001). This was due to a higher success rate in citrated accessory factors used for in vitr o tachyzoites compared to the corresponding uncitrated accessory factors us ed for in vivo tachyzoites (P < 0.001). Success in the dye test was recorde d for 48/49 and 23/23 batches of in vivo and in vitro tachyzoites, respecti vely. The number of successful dye test runs was lower with in vivo (156/23 4, 67%) than in vitro (116/142, 82%) tachyzoites (P < 0.01). Conclusions: Success in the dye test may be due to the accessory factor, ta chyzoites, or a combination of both. Problems due to the accessory factor c an be minimized by careful quality control or use of modification procedure s. Tachyzoites produced in vitro may also increase success in the dye test. Careful selection of accessory factor/tachyzoite combination makes it poss ible to use the dye test in a district general hospital. (C) 2001 The Briti sh Infection Society.