SUMMARY: Recently isolated virulent strains of grow well in a partially defined medium, but are more exacting in their growth requirements and conditions of growth than avirulent strains. The optimal pH for growth is 7.6-7.8. Mechanical agitation by stirring, spinning or aeration with either nitrogen or air, inhibits growth. Gaseous conditions, however, are critical in that there is an optimal relationship of surface area to volume of medium. Mechanical agitation and aeration stimulate the growth of avirulent strains.

Virulent strains require starch for growth, and there is a close relationship between virulence, specific agglutinability and starch requirement. Avirulent strains with low specific agglutinability grow readily in the absence of starch.

When starch in a standard medium is replaced by amylose, there is an increase in the final amount of growth. Amylopectin, glycogen and dextrans are about one-third as effective as starch; other carbohydrates, gums and inorganic adsorbents support little growth. Charcoal can replace starch, but has only 70% of its effect.

The amino-acid requirements of are satisfied by acid-hydrolysate of casein, the optimal concentration being 7%. All strains utilize aspartic and glutamic acids, serine, threonine, glycine, alanine and proline, but the rate of utilization is greater with virulent than with avirulent strains.

For good growth yeast extract is needed but can be replaced by nicotinamide, nicotinic acid or cozymase, provided sulphur-containing amino-acid is also present. Virulent strains of require a sulphur-containing acid for growth, which may be supplied by yeast extract. Cysteine, cystine or glutathione, but not methionine, act as sources of essential sulphur.


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