The lethal events in experimental Pseudomonas aeruginosa infection of mice

In Vivo Studies with the Partially Purified Protease (Elastase) from Pseudomonas aeruginosa

An extracellular protease from Pseudomonas aeruginosa exhibiting elastase activity was characterized in vivo after an 80- to 100-fold purification by chemical and chromatographic procedures. The lethality of different samples for white, female mice was determined by intravenous, intranasal, intraperitoneal, and subcutaneous injections. The purified protease exhibited the following 48-hr LD(50) values: intraperitoneally, 9.0 protease units; intranasally, 31.5 protease units; and intranasally, 0.3 protease unit. In the concentrations tested no lethality was observed when the subcutaneous route was employed. Gross and microscopic studies revealed that purified protease was capable of eliciting a variety of tissue responses in mice depending upon its route of administration. Intraperitoneal injections resulted in gastrointestinal tract serosal hemorrhage and necrosis. Intranasal and intravenous injections produced pulmonary hemorrhage, whereas subcutaneous injections resulted in black, necrotic, ulcerating lesions.

Can Pseudomonas infection in experimental animals mimic Kawasaki's disease?

Experiments aimed at producing a model of Kawasaki's disease by injecting animals intraperitoneally with Pseudomonas bacilli are described. Injection of large numbers of bacilli into mice caused rapidly fatal sepsis. With appropriate numbers of organisms, some mice died within 3 days, most remained healthy, while in some an inapparent chronic disease developed. Positive blood cultures were occasionally obtained 4-17 weeks after the slow infection. An alcohol-precipitable polysaccharide, which could be measured by Roe's procedure for levan, was found in 20% of the experimentally infected mice. We suggest that this substance was partly responsible for the course of the infection. Severe vasculitis with little acute inflammatory reaction and carditis with coronary aneurysms were often obtained by injecting mice and guinea-pigs with supraliminal doses of bacilli at the same time as their immune system was impaired by treatment with either nitrogen-mustard or cyclophosphamide. We suggest that pseudomonas infection in immunologically deficient animals may mimic Kawasaki's disease and that a similar mechanism may operate in the natural form of the disease in children.

Phagocytosis and killing of Pseudomonas aeruginosa by mouse polymorphonuclear leukocytes in vitro promoted by antiserum to the slime glycolipoprotein

The resistance of Pseudomonas aeruginosa to phagocytosis by polymorphonuclear leukocytes was overcome by opsonization with antibody to slime glycolipoprotein or, to a lesser extent, with complement. Resistance was most effectively overcome in the presence of both. Protection against viable-cell challenge conferred by anti-glycolipoprotein serum in experimental infection is discussed briefly in the light of these findings.

Rat polyvinyl sponge model for the study of infections: initial investigations

Polyvinyl sponges were implanted subcutaneously on both sides of young female rats. One sponge was infected with 10(8) of either Escherichia coli K-12 F-, Staphylococcus aureus ATCC 25923, or Pseudomonas aeruginosa CDC 7725. P. aeruginosa remained at the inoculum level and S. aureus declined by 1 log, whereas E. coli was reduced 1,000-fold. Only P. aeruginosa was recovered from the blood in 36% of the animals in 24 h and in 20% of the rats in 48 h. The nutrient potential of rat inflammatory fluid was compared to nutrient broth by growth of each bacterium in untreated and heat-inactivated sponge fluids and Trypticase soy broth.

Depression of contact sensitivity and enhancement of antibody response in Pseudomonas aeruginosa-infected mice

The effect of Pseudomonas aeruginosa infection on contact sensitivity to 2-phenyl-4-ethoximethylene-oxazolone (oxazolone) and on antibody response to sheep erythrocytes, horse erythrocytes, and Escherichia coli 0111:B4 lipopolysacharide was investigated in outbred C57BL/6 mice. Injection of 0.5 and 0.2 median lethal doses significantly depressed contact sensitivity to oxazolone, whereas injection of 0.5 median lethal dose of heat-killed microorganisms did not. The filtrate of a 24-h broth culture did not affect contact sensitivity as well. Antibody production against sheep erythrocytes, horse erythrocytes, and lipopolysaccharide (evaluated as plaque-forming cells and circulating hemagglutinin and hemolysin titers) was found to be significantly enhanced both in animals injected with living bacteria and in those which received heat-killed microorganisms. The simultaneous occurrence of depression of cell-mediated immunity and potentiation of humoral response suggests that P. aeruginosa might interfere at different levels of the host immunological responsiveness.

Inhibition of Pseudomonas aeruginosa by hyperbaric oxygen: interaction with mouse peritoneal exudate cells

High-pressure oxygen (HPO) therapy for Pseudomonas aeruginosa infections of burn wounds has not been as effective as in vitro studies predicted. Mitigation of HPO toxicity for P. aeruginosa by nutrients present at the burn site could explain the lack of in vivo success. Alternatively, HPO-induced depression of host defense mechanisms could negate beneficial effects arising from HPOs known toxicity for P. aeruginosa. Accordingly, mouse peritoneal exudate cells (PEC), preincubated for 24 h in 1 atm of air-CO(2), were used to study the in vitro effects of HPO or air-CO(2) on phagocytosis of P. aeruginosa or sheep erythrocytes (SRBC). Subsequent 2-h exposures of PEC to increasing numbers of bacteria, in an air-CO(2) atmosphere, decreased the percentage of bacteria cleared as well as PEC viability. Similar exposures of PEC to bacteria in an HPO atmosphere prevented the loss of PEC viability and increased bacterial clearance. In control experiments, increasing the number of SRBC relative to PEC decreased the percentage of SRBC cleared without decreasing PEC viability, as determined under air-CO(2); short (2 h) exposure to HPO did not affect SRBC clearance. Microscopic examination of PEC indicated that a 24-h preincubation in HPO decreased the percentage of PEC which could ingest SRBC during subsequent experimental exposures (2 h) to air-CO(2) or HPO. These data suggest that short periods of exposure to HPO promote the ability of PEC to clear pseudomonads by adversely affecting the bacteria. This in turn prevents a pseudomonad-induced depression of PEC viability and function. In contrast, prolonged HPO exposure may be detrimental to phagocytic activity.

Slime of Pseudomonas aeruginosa: in vivo production

Indirect hemagglutination inhibition tests were employed to detect slime in concentrations as low as 1 mug/ml. Increasing concentrations of slime resulted in proportionately greater inhibition of hemagglutination. Peritoneal aspirates and plasma of mice injected with slime were shown to exhibit the inhibitory activity of slime. The rapid dissemination of slime into the peripheral circulation was also indicated by the hemagglutination of mouse erythrocytes by specific anti-slime serum. By similar methods, the inhibitory activity of slime was also detected in peritoneal aspirates and plasma of mice infected with lethal doses of viable Pseudomonas aeruginosa. Furthermore, the inhibitory activity was found to increase with time after viable cell infection, whereas such increases were not detected after the injection of heat-killed organisms. Ferritin-labeled slime antibodies were found to completely surround cells of Pseudomonas aeruginosa obtained from the peritoneal cavity of mice 5 h postinfection.

Pseudomonas aeruginosa exotoxin in mice: localization and effect on protein synthesis

We studied the fate of (125)I-labeled Pseudomonas aeruginosa (PA 103) exotoxin injected intravenously into mice and the effect of the exotoxin on the protein synthesis of various organs. After 2 h, only 5% of the injected label remained in the blood, in comparison with 30% of the injected control, consisting of [(125)I]bovine serum albumin. The highest concentration of radioactivity was consistently observed in the kidneys of toxin-treated mice. Lesser amounts of the label were found in the liver and the spleen. The heart, pancreas, lung, and brain showed very little uptake. Approximately 30% of the label (non-trichloroacetic acid precipitable) was recovered from the urine within 2 h after the injection. The behavior of [(125)I]toxoid was similar to that of the [(125)I]toxin. In contrast, in [(125)I]bovine serum albumin-treated mice, the label was uniformly distributed among the organs examined, and the concentration was low. After intravenous administration of the exotoxin, a 50% inhibition of protein synthesis was observed in the liver within 4 h, and virtually complete inhibition was observed shortly before the time of death. Kidney and spleen displayed slight reduction of protein synthesis at 2 to 4 h and approximately 50% reduction during the terminal stage. It appeared that the highest concentration of the toxin occurred in the kidney, where it was degraded, but its greatest toxic effect took place in the liver.

Dissociation between results of in vitro and in vivo antibiotic susceptibility tests for some strains of Pseudomonas aeruginosa

The relative efficacy in vivo of the polymyxin and aminoglycoside antibiotics in experimental Pseudomonas infection has apparently never been established. This study was designed to determine such efficacy in experimental infection of mice. Eleven strains of Pseudomonas aeruginosa were selected for the study, representing six of the seven recognized immunotypes. All strains were susceptible to colistin, gentamicin, and tobramycin in vitro, and all were virulent for mice. None was lethal because of preformed toxins. Infections were established in mice by intraperitoneal (i.p.) injection of 100 ID(50) of bacteria (infectious doses that would kill 50% of the mice). Graduated doses of antibiotics or saline were given subcutaneously 1 h later. Infections by three strains of P. aeruginosa were cured by low doses of all three antibiotics. Infections by two strains were relatively resistant in vivo to all three antibiotics. Infections by seven strains were relatively resistant in vivo to colistimethate. For most strains, colistimethate was less effective in vivo than gentamicin or tobramycin. To determine the influence of the size of the bacterial inoculum upon the results of chemotherapy, groups of mice were infected with serial dilutions of bacterial suspensions and treated with antibiotics. The antibiotics were more effective when a lighter bacterial inoculum was used. However, colistimethate at 30 mg/kg failed to cure some infections established with an inoculum of only 10 ID(50). To examine the possibility that death despite apparently adequate chemotherapy might be due to bacterial lysis and delayed release of toxins, numbers of viable bacteria in the peritoneal cavity of treated animals were determined by colony count. Antibiotic failure by colistimethate was associated with a steady rise in the number of i.p. bacteria. The findings support the conclusion that i.p. infections in mice with some strains of P. aeruginosa that are fully susceptible in vitro are relatively resistant to chemotherapy in vivo. The dissociation between in vitro and in vivo results was greatest for colistimethate.

Sensitivity of Pseudomonas aeruginosa to normal serum and to polymyxin

Strains of Pseudomonas aeruginosa isolated from clinical material were very variable in their sensitivity to the bactericidal action of normal serum mediated by the complement system. Fifty per cent killing end points ranged from 0.015 ml to greater than 0.4 ml. Most of the strains with relatively greater sensitivity to serum were isolated from patients with cystic fibrosis. Immunization of rabbits resulted in antisera with enhanced levels of bactericidal antibody, except with one strain which was resistant to the bactericidal action of normal serum and antiserum. When P. aeruginosa was cultivated at 41 C instead of at 37 C, it was significantly more sensitive to serum and to several antibiotics, thereby implicating fever as a host defense mechanism in Pseudomonas infections. In contrast to their heterogeneity to serum bactericidal activity, the strains were relatively homogeneous in their sensitivity to polymyxin, with no apparent association between their sensitivity to the two antimicrobial agents.