I have used sucrose gradient technique in which Iwas using 12.5% sucrose to purify bacteria. But yield was quite low

Is hard to separate. But you can culture in broth and get pure bacteria

 Thanks Sir David and Antonio for answering.

Sir David my bacteria is small, gram negative cocci belongs to Pasteurella. It is P.multocida. I have loaded infected blood sucrose 12.5% and spin 4000 rpm for one hour,  all blood cell pelleted

and upper cushion is supposed to have bacteria .

When try to extract RNA  from this by Triazole method the yield of RNA was too low.