Nutritional factors affecting the synthesis of an antiphagocytic factor by group E streptococci

Effects of components of the cultural medium on formation of a group E streptococcal antiphagocytic factor (APF), as detected by an indirect bactericidal test, were studied. Bovine serum albumin (BSA) replaced serum in promoting synthesis of APF in a chemically defined medium (CDM), Todd–Hewitt broth (THB), or tryptose phosphate broth (TPB). Stimulatory factors in BSA were not retained by diafiltration membranes of nominal molecular weight cutoff limits of 10 000 or greater. Citrate, lactate, pyruvate, or oleate, often found in BSA, could not replace BSA in stimulating synthesis of APF. Cells cultured in THB were more resistant to phagocytosis by porcine leukocytes than those grown in CDM or TPB, and the addition of varying amounts of THB to CDM stimulated a measurable response in synthesis of APF. Specific substrates caused different rates of APF synthesis; in decreasing order of effectiveness were glucose or mannose, sucrose, fructose, and trehalose. Proteolytic activity, which might cause the production of phagocyte-sensitive cells by destroying APF activity during culture, was not detectable in significant amounts in subcultures of the age employed in bactericidal tests.