Streptococcus pneumoniae

Etymology
Streptococcus pneumoniae:

streptos: "chain" (from greek στρεπτός, meaning "twisted", but used medically to refer to "chains")

coccos: "berry" (from greek κόκκος, meaning "berry")

pneumonia: "inflammation of the lungs" (from greek πνευμον, meaning "lung")

Explanation
The bacteria Streptococcus pneumoniae looks like a chain (streptos) of small round berry-like cells (coccos), which causes a variety of infections, and is a notable cause of lung infections (pneumonia).

Synonyms
Pneumococcus (from pneumos meaning "lung" and coccus meaning "berry").