Effect of decalcifying agents on the staining of Mycobacterium tuberculosis

Lymph nodes from guinea pigs inoculated with Mycobacterium tuberculosis were fixed in buffered formalin, then treated for the recommended times in Gooding and Stewart's fluid, EDTA, aqueous nitric acid, von Ebner's fluid, and rapid decalcifier (RDC). The blocks were processed to paraffin wax and sections were stained by the Ziehl-Neelsen technique. Only in sections of the blocks treated with RDC were no acid alcohol fast bacilli demonstrable. Hydrochloric acid is a known constituent of RDC and it was found that Myco. tuberculosis is altered by treatment with 2-5M solutions of hydrochloric acid and above and cannot subseuqently be demonstrated by the Ziehl-Neelsen stain. From these results it is recommended that calcified tissue from patients in whom there is a suspicion of tuberculosis should be decalcified with an agent other than RDC.