Protocol Online logo
Top : Forum Archives: : General Lab Techniques

streak bacteria, what does this mean - (Nov/30/2006 )

I was given some glycerol stock e.coli. I was told not to directly grow up from the stock, but to streak it, so that i can grow it from a single colony.

what does this mean and how do I do it?



Basically it means that you will make "lines" with an inoculation loop that you have dipped into the bacteria onto an agar plate.

For example the 3 or 4 - streak method looks like this

But I guess everyone develops an own way of getting single colonies by streaking.

Then you grow the bacteria on the agar plate overnight, next day you pick a single colony to inoculate liquid medium.


Well here's the technique I usually use for streaking...

start tracing the bacterial lines with your loop according to the colors in this arrangement...

first, blue streaks
second, red streaks
third, green streaks
fourth, ochre streaks

figure 1

Notice: be sure to check the black see the direction of each streak and follow it with your loop

then leave it in the incubator for 24 hours...

then you'll get this result...

figure 2

notice I put how the colony will look like for each of the colored streaks...the more you apply the streak technique the more pure isolated colonies you the colonies from the blue streaks and ochre'll notice that the colonies in the ochre streak are less than in the blue is always advised to take the colonies in ochre be more precise try choosing from the end...because only there the colonies are most pure...but if you choose from the blue or red'll get a bunch of bacteria bundled up together which will not give you a good result for a single bacteria isolation...

if you don't get any colonies in the ochre streaks...then try green streaks..if not then red...try as much as possible to be accurate and make sure bacteria reach til the last streak...because when you do don't actually see what ur's more invisible so you'll never know if you're just tracing the agar or is there bacteria streaked with your'll only know after incubation...

so try to choose colonies from the last streak with minimum colonies...coz the result might not be as i mentioned in figure 2...

i'm sorry but i did this really quick...tell me if you want me to explain more huh.gif

-Property of Yulia-