Swarming is actually a progressive surface spreading by the microbes and essentially it occurs from the edge of parent colony. Classical examples are proteus vulgaris and proteus mirabilis. This alteration of swarming and rest occurs regularly after every 4 hours and ultimately covers whole of the media plate. This gives the appearance of growth as crescentric layer rippled or contoured
The edge of the growth at the early stages of swarming, if examined microscopically reveals long slender rods which are in continuous motion. Subsequently bundles of them break away from the edge and after travelling some distance outwards, join lateral offshoots. Thus they form arches which are rapidly filled with other rods from within. The very long rods are the predominant feature of this picture. Thus they form arches, whorl, spiral and question mark forms. However, when swarming stops, the long rods are replaced by quite short rods
Causes of swarming
Following views are expressed by different workers regarding the causes of swarming :
1. Swarming may be determined by the negative chemotactic effect of metabolites formed at the site of stationery growth.
2. Dougles attributes cessation of swarming to reduction in velocity of long forms at the edge of growth.
3. Russ-Munzer suggested the swarming because of the depletion of nutrients. However several observations reveal that its occurrence is dependent upon the composition of medium.
a) Naylor noted that swarming is inhibited in peptone meat extract agar with low electrolyte content. However, this is not because of low osmolarity of medium, if we add nutrients to it, swarming will occur.
b) A high molecular weight fraction of yeast extract enhances swarming. It is a potent stimulator of swarming even on minimal medium.
c) Jeffries and Roge observed that on a defined medium, swarming could not occur unless the contents of ordinary agar exceeded 0.8% . Perhaps extracts of agar contain a substance that stimulates swarming .
d) Smith and Alwel reported that the adition of charcoal to agar inhibits swarming and appearance of long form.
4.Morrison and scott, however, suggested that long forms of organism move continuously only when in contact with each other. By doing so they obtain thrust through sliding along one another.