Yes, LISTERIOSIS is a Scrabble word!

Letter values in Scrabble US: L 1, I 1, S 1, T 1, E 1, R 1, I 1, O 1, S 1, I 1, S 1.

Is it a valid word?

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

an infectious disease of animals and humans (especially newborn or immunosuppressed persons) caused by the bacterium Listeria monocytogenes; in sheep and cattle the infection frequently involves the central nervous system and causes various neurological symptoms

Also: listeria meningitis.