[Expansion phenomena of Proteus cultures. I. The swarming expansion (author's transl)].

The expansion of Proteus cultures on nutrient agar plates is in general attributed to negative chemotaxis with regard to a metabolic product of the culture itself. The initial latency of several hours is assumed to be the time necessary for the production and imbibition of the nutrient with the incriminated metabolite. In the present paper it will be shown that independent of this delayed expansion (expansion with initial latency) there also exists an immediate expansion that takes place when the seeded material is young (less than 12-24 hours) and rich in invasive filaments. The reaction also occurs after washing the seeded material in fresh broth. It is therefore independent of the presence of a metabolite whose production and diffusion in the nutrient substrate would have necessitated some time. It is not a question of reaction to a chemical substance but, as demonstrated experimentally, of a response to tactile stimuli. Marked thigmotaxis induced centrifugal penetration of invading filaments at the edge of the seeded droplet, between the superficial film of the suspension fluid and the surface of the nutrient agar. Heading towards the narrowest capillary spaces, groups of bacilli form, immediately after seeding, protrusions that emboss the outer contour of the droplet ("protuberances" Fig. 2, 3, 15). These protuberances continue outwards until they detach themselves from the central agglomeration. The independent bacterial "shoals" (Fig. 5, 6, 10) swarm chaotically around the seeded droplet. The total lack of orientation has been checked by numerous procedures used for recording the direction of a movement; one of this consists in recording the pathways in a latex film on agar plates (Fig. 1). This swarming phase may last 15 to 30 minutes. As the random movements in a contrary direction compensate one another, the chaotic migration of the microbial shoals would contribute little to expansion of the colony, if gradual disruption of the bacterial groups would not interfere in the meantime. Isolated individuals detached from the shoals become immobile from the moment in which they separate from the bacterial group they belonged to ("immunobilization reaction"). Therefore the migrating shoals function as organs of dissemination of the bacteria in the surrounding medium (Fig. 11). (see article).