209 Morphological Variants of Proteus hauseri

Cultures of Proteus hauseri may consist of one or more of five colonial variants. Population pressure experiments started with one variant eventually yielded all other variants. Y variants form raised non-swarming colonies on a MacConkey-type agar at 37O, but swarm in concentric step-like rings a t room temperature on this medium; they swarm in step-like concentric rings on nutrient agar a t room tempera-ture and at 37’. This variant is stable under conditions of logarithmic growth and is regarded as the wild type. Variant X is a typical Rough form and does not swarm under any circumstances. In continuous culture i t mutates to the Y type a t a high rate. The W variant forms colonies very similar to those of the Y variant, but like the X variant does not swarm. It is stable under conditions of continuous culture, but mutates on MacConkey agar to X and Y variants at low rates. On MacConkey agar at 37 ’ the Z type appears as a flat amorphous colony surrounded by a con-tinuous thin film of swarm. It also swarms at room temperature. This variant is replaced by a mixture of Y and W colonial forms in continuous culture experiments. Drop-like colonies, the ‘ Tropfchenform ’ previously described by Weil & Felix (1917