Viability and Metabolism of Staphylococcus Aureus after Freezing, Lyophilization, and Irradiation.

Ahn, T. H. (University of California, Los Angeles), H. Nishihara, Charles M. Carpenter, and G. V. Taplin. Viability and metabolism of Staphylococcus aureus after freezing, lyophilization, and gamma irradiation. J. Bacteriol. 88:545-552. 1964.-Reproductive viability and oxidative activity on various substrates (alanine, glutamic acid, glucose, lactic acid) were studied in Staphylococcus aureus cells subjected to (i) freezing and thawing, (ii) lyophilization, (iii) irradiation in suspension, (iv) irradiation in lyophilized state, and (v) lyophilization and irradiation in the presence of various substrates. Freezing and thawing in dilute albumin solution had no effect on viable cell count and on lactic acid oxidation, but the oxidation rates of alanine, glutamic acid, and glucose were decreased. Lyophilization reduced the viable cell count to 25 to 30% of the initial value, and decreased the oxidation rates of glutamic acid and alanine proportionally, whereas decrease in glucose oxidation was less than proportional. The lactic acid oxidation rate was not affected by lyophilization. An irradiation dosage of about 40,000 r was required to reduce the viable count of cells irradiated in suspension by one log(10) unit; lyophilized cells required 140,000 to 170,000 r. Cells irradiated in suspension with dosages sufficient to render them completely nonviable on culture continued to respire on lactic acid at about 60% the rate of nonirradiated cells, but the residual activities on the other substrates tested were less than 10 to 12%. Lyophilized cells irradiated with sufficient dosages for cultural nonviability retained 40 to 80% of the oxidative capacity of nonirradiated cells on the test substrates. Cells lyophilized and irradiated in the presence of albumin generally retained a greater portion of their oxidative activities compared with cells lyophilized and irradiated in buffer. Cells irradiated in the presence of various oxidizable substrates gave varying results, depending both on the substrate present during irradiation and the substrate added for the oxidative studies.