The spreading of some Proteus species on solid culture media, a feature possibly of the extreme motility of the organism. A variety of methods (none wholly satisfactory) have been devised to prevent the phenomenon, including : (1) high (4 -6 per cent) agar content; (2) electrolyte-free agar; (3) treatment of the inoculum with ether; (4) inclusion in the medium of substances such as chloral hydrate (1 – 500) or sodium azide (1 – 5000).
The spread of bacteria over a culture medium.