Trace elements incorporated into the culture medium of Mycobacterium tuberculosis promote the presence of tuberculoprotein C in the preparation of purified protein derivatives.

Two purified protein derivatives (PPDs) were prepared from Mycobacterium tuberculosis, H37Ra. One of the PPDs was prepared from the culture filtrate of organisms grown on Proskauer-Beck medium to which trace elements had been added. The other PPD was prepared from the culture filtrate of organisms grown on the same medium but without trace elements, and was used as the control. Comparative skin reactions in sensitized rabbits showed that the PPD prepared from organisms grown in the presence of trace elements was less potent than the control. Since it has long been recognized that of the many tuberculoproteins present in PPD, the C protein (a 44 to 66 kDa protein) was always the least potent fraction when tested in equivalent concentrations in both serological and skin test assays, the possibility existed that the PPD obtained from organisms grown in trace element medium had more of the C protein complex than the control. Comparative studies of these two PPDs in terms of their chemical composition, skin test responses, and electrophoretic profiles obtained by SDS-polyacrylamide gel electrophoresis provide support for this assumption.