Coccidioidin and merthiolate in previously sensitized animals.

The effect of merthiolate, which is used as a preservative in skin test materials, on skin test reactions was determined in guinea pigs. In four groups of animals, merthiolate in basal medium produced skin tests at 24 and 48 h characterized by erythema and/or induration in an intermediate region, i.e., 5 plus or minus 2.2 mm. One of the four groups of animals was a nonsensitized control group. The other three groups were subcutaneously sensitized with (i) merthiolate and saline, (ii) killed Coccidioides immitis arthrospores, and (iii) merthiolate with killed C. immitis arthrospores. Coccidioidin only and merthiolate in coccidioidin produced positive delayed results in groups 3 and 4, which were sensitized with arthrospores. A synergistic effect of merthiolate and coccidioidin was observed in animals of group 4 sensitized by merthiolate with killed C. immitis arthrospores. This effect was observed at 24 h when positive reactions of coccidioidin with merthiolate were significantly greater than skin tests with plain coccidioidin.