The Cultivation of Bacterium tularense in Embryonated Eggs

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Abstract
An adaptation of glucose cystine blood agar is described in which cysteine-HCl is sub-stituted for cystine. This medium has been shown to be suitable for making surface plate counts of Bacterium tularense [Pasteurella tularensis] and the technic for plate counts is described. The enumeration of B. tularense from standard suspensions by this method has been compared with mouse titrations and has been shown to be accurate. This method has been used in the enumeration of B. tularense grown in embryonated eggs. B. tularense multiplies abundantly in the tissues of embryonated chicken or duck eggs. Multiplication is greategt in the yolk sac, particularly after yolk sac inoculation. The property of virulence affects the multiplication of the organisms in the embryonated egg and the survival of the embryo. The virulence of B. tularense for chick embryos is enhanced on serial passage through embryonated eggs. Storage in the frozen state or in the cold, preserves, for a period of 3 months, approx. 1% of the original number of organisms present.
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