On the nature of bacteremia in experimental pneumococcal pneumonia in the dog. II. Disappearance of pneumococci from the circulation in relation to the bactericidal action of the blood in vitro

Studies on bacteriemia. V. The effect of simultaneous leukopenia and reticuloendothelial blockade on the early blood stream clearance of staphylococci and Escherichia coli

Observations are presented on the course of experimental bacteriemia in rabbits modified by thorotrast reticuloendothelial "blockade" and mechlorethamine induced leukopenia, given singly and together. The production of severe granulocytopenia did not impair the clearance of staphylococci from the blood stream and did not enhance the impairment of clearance produced by thorotrast reticuloendothelial "blockade." Neither severe granulocytopenia nor thorotrast blockade alone produced consistent impairment in the removal of circulating E. coli from the blood stream, whereas when these conditions were present together, the early phases of clearance in these animals were virtually prevented. These results indicate that the host mechanisms operative in the control of bacteriemia differ for staphylococci and E. coli. It is suggested that the fate of bacteria within polymorphonuclear leukocytes may in part determine the importance of these cells in the removal of bacteria from the blood stream.

Studies on bacteriemia. III. The blood stream clearance of Escherichia coli in rabbits

Large numbers of E. coli were rapidly removed from the blood stream of rabbits at rates which initially paralleled the removal of similar numbers of staphylococci. Splanchnic tissues removed approximately two-thirds of the circulating bacilli in transit through the liver and spleen. In contrast to the cessation of splanchnic trapping noted 20 to 40 minutes following the injection of staphylococci, splanchnic trapping of E. coli continued unchanged for 3 to 5 hours unless the splanchnic tissues were dearly reseeding the blood stream. This resulted in the continued disappearance of E. coli over a 60 to 90 minute period, and differed from the constant bacteriemia maintained beyond 20 minutes after the injection of staphylococci. Some of the differences in the initial clearance of these two microorganisms appeared to relate to differences in host leukocyte-bacterium relationships. In vitro studies indicated that E. coli were rapidly killed following ingestion by rabbit polymorphonuclear leukocytes. Staphylococci survive such ingestion. The injection of E. coli was followed by a prolonged granulocytopenia with evidence of sequestration of granulocytes within the pulmonary vascular bed. The injection of staphylococci was followed by a transient leukopenia, with rapid return of granulocytes to the circulation (15). It appears probable that E. coli ingested by sequestered leukocytes are destroyed within the cell, and that leukocytes do not reenter the circulation containing living E. coli. Such intraleukocytic residence in the blood stream has been shown to be of possible importance in the maintenance of staphylococcal bacteriemia (14). An increasing E. coli bacteriemia occurred rapidly after the initial clearance period, indicating that many sequestered bacilli remained viable. Increasing bacteriemia also occurs 3 to 5 hours after the injection of staphylococci. The bacterial or host cell mechanisms which allow this secondary resurgence of bacterial populations are currently under investigation.

Studies on bacteriemia. I. Mechanisms relating to the persistence of bacteriemia in rabbits following the intravenous injection of staphylococci

During the course of studies on the characteristics of experimental bacteriemia, staphylococci were swiftly cleared from the blood stream of rabbits during the initial 10 to 15 minutes following intravenous injection of microorganisms. A subsequent abrupt decline in the rate of clearance ensued, resulting in a low grade bacteriemia which was demonstrable for many hours. The experiments reported have indicated that this strain of staphylococcus is rapidly phagocyted within the vascular system of rabbits, and that viable staphylococci circulate within the cytoplasm of polymorphonuclear leukocytes. The removal mechanisms contained within the liver and spleen appear to preferentially trap circulating extracellular staphylococci. When most of the circulating staphylococci are contained within leukocytes, splanchnic removal declines or virtually ceases. These observations suggest that viable, intracellular microorganisms are responsible for the persistence of staphylococcal bacteriemia in rabbits following the phase of rapid removal from the blood stream.