Factors affecting the yield and biological activity of lipid extracts of Listeria monocytogenes

Abstract

The biological activity of lipid extracts of five strains of Listeria monocytogenes was studied, with special reference to their monocytosis-producing activity in mice. Two of the strains gave more active extracts than the others, and cells grown at 4 C produced more lipid with better activity than cells grown at room temperature or at 37 C. Extracts obtained from cells harvested at the various stages of log phase at 4 C all gave similar levels of monocytosis in mice. The level of monocyte response varied from animal to animal, but in general, older mice (28 to 48 weeks) responded better than young mice (9 to 15 weeks) and females gave a better response than males. These extracts also produced leucopenia in young mice, but this was less consistent and leucocytosis was more often observed in older mice. Granulocytosis and lymphopenia were commonly found in mice injected with lipid extracts of L. monocytogenes. These changes were affected by the strain of bacteria but not by the age and sex of the test animals. The changes in blood picture normally reached a maximum 1 to 2 days after injection and returned to normal after about 5 days.