glass beads for plating bacteria to get an even distribution on agar

Pete Muriana MURIANAP at FOODSCI.PURDUE.EDU
Sat Dec 10 09:57:15 EST 1994


>In article <3c098h$3sc at nuscc.nus.sg>
>phstayhn at leonis.nus.sg (Dr Tay Hou Ngee Agnes) writes:

>> Hi, Does anyone know a supplier and catalog no for glass beads used to 
>> spread bacteria in transformation (instead of spreader made from pasteur 
>> pipet)? Please reply to phstayhn at leonis.nus.sg
>> Thanks
>> Agnes

Yes, I've used the "glass bead" method since around 1985 when I picked it up 
from some friends during my graduate work - it's my preferred method of 
surface plating because it spreads the cells so homogeneously on the plate 
that you can never get such an even distribution of colonies with a glass 
hockey stick (at least I could't :>).

Fisher Sci. sells "Economical solid glass beads" ; we use their 4 mm beads 
(#11-312B; $19.00/lb).

For those interested in how to use them:
   1. distribute to small test tubes (13mm x 100mm) using a small funnel; 
	usually 4-6 per tube is sufficient; we usually make one or two racks of 
	tubes at a time; autoclave them to sterilize.

   2. When plating (after sample is aliquoted onto the agar), uncap a tube and 
	pour the beads onto the plate; stack the plates and slowly shake them 
	back and forth; every few seconds turn the stack; the idea is to have 
	the beads travel back and forth along the diameter of the plates, not 
	the periphery!; usually about 2-3 min. is sufficient; I can do up to 10 
	plates at a time (I've got big hands :>).

   3. When done, tilt a plate on its side, crack it open and pour the beads 
	into a waste container (preferably containing sanitizer).  When you collect 
	enough "spent" beads, we usually add soap and autoclave them, then rinse 
	with deionized water, decant excess water, and let them dry for reuse!

This is great for getting evenly-distributed colonies either for plate counts, 
colony-lifts, etc.  Guaranteed once you try it, you won't plate by any other 
method.
-Regards, Peter
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*  Peter M. Muriana, Ph.D.             317-494-8284   TEL            *
*  Dept. of Food Science               317-494-7953   FAX            *
*  Purdue University                   murianap at foodsci.purdue.edu   *
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