If you have a mixed broth, (or a mixed slant culture) your first step
will be to take a loopful of the broth (or, from a slant, a straight
loopful of colonies that resemble the ones you are hoping to isolate)
and streak it for isolation onto various types of agar, including
non-selective agar such as sheep blood agar, and some selective media
such as Thayer-Martin, MacConkeys, PEA, HE, etc. The kind of organism
you are hoping to isolate will determine what type of selective media
you will use. Most all types of organisms will grow on blood agar,
while MacConkeys?s will inhibit growth of gram positive organisms,
allowing gram negative organisms to grow, making for easier isolation.