strange growth of colonies - (May/21/2008 )
Hi!I've got anther question that takes me a lot of trubles..I'll try to explain it...sometimes on my plates count agar I see the normal growth of colonies but when they are quite big (after 24 h more or less) I can see a kind of alone (it's similar to condensaton but I don't know if it coul be) that spreads very quickly from a point of the plate and invades hour after hour all the plate so I can't count the colonies anymore!!But the strange thing is that when I plate the same sample in various plates this effect doesn't happen in all the plates!Have you ever seen something like that?Thanks a lot!
Sounds to me like either a crazy mold or Proteus spp.
If you are talking about bacterial colonies in antibiotic agar plate, it may be satellite colonies that appear in the ever-widening circle around real colonies. Perhaps you already know about'em, but just in case..
My tip would be: motile bacteria like - as suggested before - Proteus spp. (often very very bad smell 
)
)A good one. If that is the case, you can increase the % of agar in your plate. That would reduce the motility dramatically. Say 1% -> 1.5% agar.
Thank you for your replies... but probably it's not proteus.....and my question now is: can some motile bacteria spread out of a colony on the surface of the agar plate and create that alone around it?I can't increase the content of the agar in my plate because I've only got plates ready for the use (poured) or disidratated medium (Idon't prepare it by myself..).
Bye Bye!!
Bacillus spp. can also produce the spreading phenomenon you described.
You can use pour plates - esp. with a second very shallow layer of agar poured on the inoculated plate after it's set up before inoculation.