Sensitivity of serologically classified strains of escherichia coli of human origin to the serum bactericidal system

In vitro interaction of Bacteroides fragilis with polymorphonuclear leukocytes and serum factors

The sera and polymorphonuclear leukocytes (PMNs) of healthy human subjects were tested against several isolates of Bacteroides fragilis. All sera killed most of the fecal isolates, but were active aganist only one of the clinical isolates. The degree of killing was directly related to the serum concentration but was independent of the bacterial inoculum within the range of bacterial concentrations studied. The serum bactericidal activity was heat-labile. Engulfment and killing of B. fragilis by PMNs were demonstrated consistently. The opsonim involved in phagocytosis was also heat liable. Calculations involving log-transformed data permitted the quantitative study of the separate and combined effects of serum and PMNs on bacteria which were killed by serum alone. Whereas serum alone usually killed 0.5 log of serum-sensitive bacteria, the addition of PMNs was usually associated with one log further killing. The studies reported here demonstrate the presence of heat-labile serum factors in normal human sera which killed B. fragilis directly and which promote its phagocytosis and killing by PMNs. These observations provide a foundation for investigations into host defense mechanisms against anaerobes.

Sensitivity of some smooth strains of Escherichia coli to the bactericidal action of normal human serum

The sensitivity to normal human serum of 144 smooth strains of Escherichia coli isolated from cases of urinary tract infection was determined. It was found that serum-sensitive and serum-resistant strains were not randomly distributed throughout the 10 O serogroups commonly associated with urinary infection. A similar distribution was observed when a group of strains isolated from rectal swabs was studied. The results indicate that serum resistance may be related to qualitative characteristics of the O antigen.

Escherichia coli bacteremia in the squirrel monkey. I. Effect of cobra venom factor treatment

Squirrel monkeys were significantly depleted of complement by a nontoxic protein constituent of cobra venom, and the influence of cobra factor (CoF) treatment on the course of Escherichia coli bacteremia was studied. Striking neutropenia occurred rapidly in control animals while the rate of occurrence of neutropenia was 20 to 30 times slower in the CoF-treated animals, suggesting that the E. coli-induced neutropenia was at least partially a complement-mediated response. In the CoF-treated monkeys, the initial rate of clearance of the E. coli from the circulation tended to be slower and the resultant levels of bacteremia were higher than in control animals. These observations are consistent with a hypothesis that complement-mediated neutrophilic leucocyte function is an important host defense mechanism in gram-ngeative bacillary bacteremia.