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Published online by Cambridge University Press: 15 May 2009
A strain of Proteus vulgaris, recovered from a case of cystitis, showed extreme pleomorphism in a primary culture on ordinary agar.
Pleomorphism was not found in sub-cultures on media free from added NaCl, but it appeared in the presence of a limited range of NaCl concentrations; with still higher concentrations it was not observed, although growth occurred. It was rarely found in cultures which grew with difficulty.
Pleomorphism, occurring under the conditions mentioned as to salt concentration, was most marked in young cultures which grew vigorously; it usually disappeared as the cultures aged; and it became less and less evident in serial sub-cultures on medium containing the same amount of salt.
The morphology of the organism differed on different media, e.g. filamentous on salt-free agar, short bacillary on MacConkey's agar, but it was practically constant in repeated sub-cultures on any one type of medium.
Pleomorphism could be re-induced on any of the media used by suitable alteration of its NaCl content (increase or decrease). Pleomorphism was not determined by variation of the H-ion concentration of salt-free media; nor by variation of the temperature of incubation of cultures; nor by growth in fluid media as opposed to solid media.
After nearly 4 years under laboratory conditions the organism is still sensitive to variation in the NaCl concentration of its environment, as evidenced by pleomorphism; but pleomorphism is now less extreme than it was originally.
Pleomorphism is still most marked in young sub-cultures on media with suitably altered salt concentration, but it is sometimes difficult now to induce pleomorphism unless a stock culture several weeks old is used as the inoculum.
The pleomorphism comprises aberrant forms similar to many of those which are regarded by certain observers as evidence of stages in a life cycle; but, in the case of the organism described, these forms can be induced by the simple expedient of altering the salt concentration of the medium on which it is grown. The occurrence of such forms is thus, of itself, no proof of a life cycle.
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