Analysis of protective mechanisms against infection by Serratia marcescens

The present paper is concerned with an experimental study of effects of some agents on parameters pertinent to host resistance to infection of Serratia marcescens (S. marcescens) which was isolated from a patient. The results obtained are the following: In the control mice injected intravenously with S. marcescens, most of the bacteria were trapped in the liver, spleen and lung, the so-called reticuloendothelial system (RES), and the number of bacteria decreased gradually with time. In the kidney, the bacterial count did not decrease because of the existence of few macrophages in this organ. In the animals treated with X-irradiation and cyclophosphamide, the mortality rate increased, and the number of S. marcescens in the organs increased significantly with time. These observations were irreversible in the X-irradiated group, but were reversible in the cyclophosphamide-treated group, depending on the challenge dose. In the mice treated with carrageenan, which functions as a macrophage blocker, the mortality rate did not increase significantly, but there was a delay before the bacteria were eliminated from the liver indicating that the bacteria were not killed in the early phase. After intraperitoneal administration of proteose peptone, polymorphonuclear cells (PMNs) and macrophages accumulated in the peritoneal cavity on the 1st day and 4th day. When S. marcescens was injected intraperitoneally to these 2 groups. The 50% lethal dose (LD50) did not increase significantly in each group. After intraperitoneal inoculation of S. marcescens in a dose equal to 1.5 LD50 in normal mice, the elimination of bacteria from the peritoneal cavity was very rapid in the mice pretreated with proteose peptone.(ABSTRACT TRUNCATED AT 250 WORDS)