Yes, STREPTOCOCCI is a Scrabble word!

Letter values in Scrabble US: S 1, T 1, R 1, E 1, P 3, T 1, O 1, C 3, O 1, C 3, C 3, I 1.

Is it a valid word?

STREPTOCOCCI is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

spherical Gram-positive bacteria occurring in pairs or chains; cause e.g. scarlet fever and tonsillitis
spherical Gram-positive bacteria occurring in pairs or chains; cause e.g. scarlet fever and tonsillitis