Chick embryo, a model to study the lethal activity of pertussis toxin, infectivity of Bordetella pertussis, and their neutralization by immune sera

Abstract

The toxin activity of Bordetella strains and acellular pertussis components was evaluated in chick embryos. Eleven-day-old embryos were found to be most suitable for determination of LD50 values. Eight of eight Bordetella pertussis strains possessed LD50 values of 104 to 106 colony-forming units per dose of 100 μL. Embryos were resistant to Bordetella parapertussis and Bordetella bronchiseptica at doses of 1010 colony-forming units. Bacterial growth did not occur in the bloodstream or tissues of the heart, kidney, brain, liver, or lungs. Pertussis toxin activity, determined by clustering of Chinese hamster ovary cells, was found in the allantoic fluid following inoculation of virulent bacteria. Purified pertussis toxin had an LD50 of 1–2 μg protein/dose. Striking pathological effects of liver necrosis and oedema of the head and neck were similar following bacterial or toxin inoculation. Widespread changes occurred in the liver at the perivascular level, suggesting that after allantoic inoculation of virulent Bordetella strains, toxin is secreted, carried in the bloodstream, and causes the resultant pathology. Purified B. pertussis lipopolysaccharide was nontoxic for embryos at doses containing 30 μg; filamentous haemagglutinin was nontoxic at doses up to 10 μg. A correlation exists between the ability of serum to neutralize killing of chick embryos by toxin and to neutralize clustering of Chinese hamster ovary cells by toxin. Although the chick embryo serum neutralization studies confirm observations of mouse intracerebral infection studies that antibody to pertussis toxin is not an absolute requirement for prevention of infection with B. pertussis, evidence is provided that anti-toxin will eliminate toxic effects owing to secretion of pertussis toxin.Key words: Bordetella, pertussis toxin, chick embryo.