Relation of colonial morphologies in soft agar to morphological and biological properties of the K-9 strain of Klebsiella pneumoniae and its variants.

During repeated subcultures of strain K-9 of Klebsiella pneumoniae, three variants, A, B, and C, were obtained showing different colonial morphologies in soft agar. The parent strain K-9 produced colonies that were large, smooth, and globular; variant A, wedged balloon forms somewhat elongate; variant B, rain-drop-like with some streaming; and variant C, small compact rough globules. These colonial forms in soft agar medium correlated well with the size of capsule determined by cell volume index and light microscopy. Organisms exhibiting large globular colonies did possess extra large capsules while strains producing compact-type colonies in soft agar were lacking capsules. Capsular size of the strains correlated well with mouse virulence, but most biochemical properties, including the amount of endotoxic substance, were the same in all strains.