Bacterial Invasion is a level-based puzzle game in which you are a bacterium infecting a human body. Or rather, sort of; the analogy inspires the design, but this is no sim. "Infection" doesn't mean breeding wildly in vivo and outspawning the immune system; instead, it apparently means finding the spawn points for leucocytes and "infecting" them, at which point the game transitions to the next level.
Motion is with the mouse. Left mouse button is "infect" mode, and in this mode you may consume red blood cells (which restore health if you've lost some), and also "infect" walls. The only effect of this is that infected walls attract nearby white blood cells, which restore them to health, but this may be useful in distracting opponents.
The right mouse button puts you into "defensive" mode; in this mode, if a white blood cell encounters you, you become smaller, and immune to white blood cells until you re-enter infect mode. This allows you to sneak past enemies -- and also, since you are smaller, to travel through some areas otherwise blocked to you.
Typically, a puzzle game has a handful of elements out of which it rings the changes of possible puzzle configurations, and that's what the developers have done in this Game Jam product; though there are a limited number of levels, they each offer a different challenge. For a 48-hour game, it's quite well executed.
It is, as you might expect, also a bit rough; you cannot voluntarily restart the level, and there are times when you can trap yourself in an unsolvable state. The soundscape is sparse, without music, and there are occasional bugs. But it's still much more original than most game jam titles.