Cultivation of Bacterium tularense in Peptone Media.

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Abstract
[plus or minus]Each of the 28 virulent and avirulent strains tested could be cultivated in a medium consisting of 2% Bacto peptone, 1% NaCl and 0.1% dextrose. At least 9 consecutive transfers were tested with each strain. Large inocula (1-10% transfers) were required, especially in the case of the less virulent strains. The minimum effective inoculum was reduced by incubation under decreased O2 tensions, or by the addition of reducing agents (0.1% cysteine-HC1 or 0.01% thioglycolic acid). Aeration increased the final yield to a maximum of 3-10 billion organisms per ml. in 24 hrs. at 37[degree]. The rate of growth, but not the final yield, was decreased by incubation at 25[degree]. Virulence for mice was reduced from the usual 50% lethal dose of 0.2-3 organisms in 2 of 5 series carried 50 passages at 37[degree], but not in any of 5 series carried 50 passages at 25[degree]. Each of 3 strains tested could be cultivated on peptone agar slants. Growth in peptone agar shake cultures occurred in a single layer parallel to the surface and at various depths depending on the strain and number of organisms inoculated. It was concluded that B. tularense is an obligate aerobe, the growth of which is inhibited by a mildly oxidizing environ-ment, but there was no indication whether inhibition is refer-able directly to O2 or to oxidation of the medium.

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