after identifying pneumococcus bacteria, i store it using 30% glycerol at -80 C. One month later i tried to reisolate it. All i have is a sterile blood plate with no growth.
if your bacteria did not suffer from an osmotic shock, so try to cultivate an aliquot of your -80 store in a liquid medium ( its like an enrichment step )for 24h or 48h in an adequate temperature, and after that plate from this liquid medium culture in a petri dish solid medium, and i hope you will find some bacterial colonies.
and take in the account that you shoul to prepare two bacterial stocks : one for long term in -80, and one in inclined tubes if you always need your bacterial strain.
It is convenient to use glycerol 10-20%, for some bacteria higher concentrations can be toxic.
You can also add selective supplements for streptococcus to the blood agar that enhance growth
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