Influence of Phosphate on Stability of Crude Penicillin

Fermentation studies on Penicillium notatum in surface cultures suggested that a correlation, independent of buffer action, exists between the concentration of KH2PO4 initially present in the culture medium and the maintenance of a relatively high degree of antibacterial activity in the crude penicillin (8). The term "penicillin" is used here in its osriginal sense as defined by FLEMING (6) to designate the mold-free filtrate obtained from cultures of Penicillium sp. This problem has been investigated further and is the subject of the present report. The instability of penicillin in aqueous solutions, especially in certain pH ranges, is well recognized. It was shown in 1942 that maximum stability occurs between pH 5.5 and pH 7.5 (2), and more recently a thorough study of the stability of pure and partially purified penicillins in aqueous solutions at different temperatures and at different hydrion concentrations has been published by the Northern Regional Research Laboratory (3). Concerning unpurified crude penicillin, using the term in Fleming's original sense, it was observed (1) that maximum titres were found in the medium when the pH was about 7.0. Subsequently, attempts were made to maintain a favorable pH in the fermentation medium by use of suitable phosphate buffers (5) after it had been suggested that penicillin in crude fermentation liquors may be rapidly destroyed by the biological production of excess acidity (4). Early experiments in this laboratory suggested, however, that suitable mixtures of inorganic phosphates might exert a stabilizing effect independent of buffer action on crude penicillin, and soon after the present experiments were begun, it was suggested that a similar effect might be observed in partially purified preparations (10).-