CONDITIONS INFLUENCING THE DISAPPEARANCE OF LIVING BACTERIA FROM THE BLOOD STREAM

Modeling bacterial clearance using stochastic-differential equations

Capillary - tissue fluid exchange is controlled by the blood pressure in the capillary and the osmotic pressure of blood (pressure of the tissue fluid outside the capillaries). In this paper, we develop a mathematical model to simulate the movement of bacteria into and within a capillary segment. The model is based on Fokker-Planck equation and Navier-Stocks equations that accounts for different boundary conditions. Also, we model the transportation through capillary walls by means of anisotropic diffusivity that depends on the pressure difference across the capillary walls. By solving the model with a numerical method, it was possible to predict the concentration of bacteria at points within the capillary. However, numerical analysis consumes computational time and resources. To efficiently simulate the bacterial clearance, we propose a segmentation model that is based on breaking the capillary network into smaller sections with pre-defined properties in order to reduce the overall computational time. The proposed model shows a great reduction in computational time and provides accurate results when compared to the numerical analysis.

Duration, prevalence and intensity of bacteraemia after dental extractions in children

OBJECTIVE

To investigate the duration, prevalence and intensity of bacteraemia after dental extractions in children by comparing within-patient bacteraemia before and after dental extraction.

METHODS

Children were randomly allocated to one of 10 postprocedure time groups from 10 s to 60 min. The differences between intensity and prevalence of the bacteraemia at each time after extractions were used to estimate the duration of the bacteraemia. After attainment of general anaesthesia, pre-extraction and postextraction blood samples were processed by broth culture and lysis filtration to isolate and quantify bacteria present in the patients' blood.

RESULTS

500 subjects between 3 and 16 years old were recruited. The estimated duration of bacteraemia was about 11 min.

CONCLUSIONS

The duration of bacteraemia after dental extractions is less than previously thought. This has implications for the interpretation of odontogenic bacteraemia studies.

The splanchnic removal of bacteria from the blood stream of leukopenic rabbits

In rabbits subjected to profound damage of the blood-forming tissues by the use of benzene and mechlorethamine hydrochloride, no impairment of efficiency in the splanchnic removal of M. aureus from the blood stream could be demonstrated by a method involving catheterization of the hepatic vein. All evidence continues to indicate that a bacteriemia cannot be maintained unless the organisms are introduced constantly into the blood stream from some source. The importance of the leukocyte in the establishment and clearing of the bacteriemias appears to lie in its phagocytic activities at the local source of the bacteriemia rather than in any quantitatively significant phagocytosis of organisms circulating in the blood stream. The present studies suggest that in the study of the leukopenic state attention should be directed more especially toward the identification and eradication of the local source of organisms.

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.

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

With the purpose of ascertaining the influence exerted by the pneumococcidal activity of the blood on the course of bacteremia occurring in experimental canine pneumococcal pneumonia, a study was made of the rates at which intravenously injected pneumococci disappeared from the circulation and the shed blood of diseased dogs. Preliminary studies on normal animals showed that blood containing hundreds of thousands of pneumococci per cc. immediately after injection usually became sterile or nearly so within an hour's time. Simultaneous observations carried out on the blood in vitro showed an analogous rapid disappearance of the microorganisms, although the effect was not quite as marked. Similar tests on non-bacteremic dogs with pneumonia revealed essentially the same ability of the body to dispose of large numbers of circulating pneumococci. The shed blood likewise exhibited marked bactericidal power. The occurrence of bacteremia during pneumonia did not retard greatly the rate at which injected pneumococci disappeared from the circulation, as compared with the non-bacteremic state. After several hours the numbers of circulating microorganisms were approximately the same as prior to the intravenous injection. Blood in vitro often cleared as fully as it did in vivo over the same length of time. Studies on the role played by humoral immune substances in the bactericidal action of the blood showed that while their presence was necessary for maximum killing power, and that bacteremic blood lacking humoral immune properties was rarely capable of self-sterilization in vitro, nevertheless such blood often retained considerable bactericidal potency as shown by its ability to reduce materially the numbers of pneumococci added to it. This phenomenon is discussed. The marked pneumococcidal capacity of the blood exhibited by dogs with experimental pneumococcal pneumonia and its persistence during bacteremia suggest that this constitutes the principal mechanism for limiting the degree of blood invasion. The similarity of the findings in canine and human pneumococcal lobar pneumonia is pointed out.