A polypeptide skin test antigen from Nocardia asteroides

Nocardin Active Polypeptide (NAP-A), derived from 3 different strains of Nocardia asteroides, was tested for species and strain specificity in guinea pigs, sensitized to 9 species of Nocardia and Streptomyces. There were no cross-reactions with genera other than Nocardia. NAPA-A was specific for N. asteroides. Cross-reactions occurred with N. caviae and only 1 strain of N. brasiliensis. Quantitative differences in specificity were found between various strains of N. asteroides. Thus, the combined antigen, derived from 3 strains of N. asteroides, was found to be the most consistent in producing positive and specific reactions in animals, sensitized to the various N. asteroides strains used in this study. The combined antigen, also, minimized the occasional cross-reaction incurred with N. brasiliensis.