Haemophilus influenzae

Etymology
Haemophilus influenzae:

haemo: "blood" (from greek αἷμα (haema), meaning "blood"). Similar words: hematology, hematocrit, etc.

philus: "fondness" (from greek ϕιλία (philia), meaning "friendship" or "fondness"). Similar words: hydrophilic, etc.

influenzae: "to flow in" (from latin influĕre, meaning "to flow in"). Similar words: influence, flow, influx, etc.

Explanation
The bacteria Haemophilus influenzae is an opportunistic pathogen that, in order to multiply and cause an infection, requires a complex set of nutrients which is provided by the blood (haemo), so it likes, or is "fond of" (philus) the blood. I remember it this way: isolating H. influenzae from the blood or CSF is indicative of an infection (since it likes blood but normally can't live there so it doesn't grow in an uncontrolled fashion), but isolating it from the nasopharynx or sputum doesn't indicate infection, since these areas are normally colonized by it. It was originally thought to be the cause of the flu (influenzae), but now we know that the flu is viral in origin.