"Bacteria" is the name given to an individual (or possibly a species) of bacteria-based creature formed in, and currently inhabiting, the Complex.
Three (possibly four) different variations of Bacteria have been observed so far. While there is no clear evidence as to whether these are simply variations of the same being, or distinct and separate entities of the same species with similar elements, there are many things that set them apart, like their shape, behaviour, and especially the sounds they produce. Considering the mysterious time-altering properties of the Complex, the different variations could very well be the same Bacteria at different stages in life.
Its body is a dark, moldy brown, sporting elongated arms reaching all the way to the ground and an appearance that can be described as "a stick-figure body made out of pipe-cleaner", with twisting wire-like shapes enveloping it. It has no discernible features on its face, instead appearing as a bumpy swirl of material with no consistent shapes.
The only direct human encounter with this variation that we know of is shown in Found Footage, in which the Bacteria displays extremely hostile behavior. It stalks the recently-noclipped Kane Parsons (in-universe) for several minutes as he explores the Complex. This "stalking" behavior may indicate either some level of intelligence, or at the very least sophisticated hunting instincts that allow it to hunt prey. After some amount of time, perhaps when the Bacteria deemed him vulnerable enough, it began emitting a low-pitched scream whilst sprinting towards him. Despite being an effective scare tactic, this is unfortunately not an ideal hunting strategy. It is also capable of no-clipping through walls, and will sometimes use this to catch up. The Bacteria will continue to scream and chase its prey non-stop until it either catches them, or their prey manages to escape. (In the case of Kane's initial encounter, he escapes through a hole in the floor).
Much like the stick-figure variation, this one has a dark, moldy brown body, with elongated arms. The "twisting wire" look is less prominent, and it appears more solid and "hardened" in comparison, with two stilt-like legs. Most notably, its (presumably) long neck is much thicker, and bent forward at a freakish 90° angle.
This variation has only been seen for a few brief few seconds towards the end of Found Footage, while Kane is hiding behind some walls. It is seen walking very slowly with its thin, stiff legs, searching for Kane while making some sort of "creaking" noise. Before it comes into view, it (or possibly another creature nearby) can be heard stomping, howling, breathing heavily, and making loud, owl-like "HOO!" sounds.
At the very end of Found Footage, when Kane thinks he is safe and the stomping footsteps can be heard receding and becoming quieter, an inquisitive "HOO?" is suddenly heard from behind him. When he turns around, a Bacteria grabs and, presumably, kills him. It is unknown if this is one of the two from before, or a new individual, though it looks closer to the stick-figure variation.
It has a "power mast"-like body compared to the other Bacteria, with limbs that look very stiff. Unlike the Hunched variation, its legs are very long. One of its arms also appears thicker than the rest of its body.
During Pitfalls, this Bacteria lures ASYNC employee Marvin E. Leigh towards itself by imitating the yelling of a survivor, screaming things like "Does anybody hear me?", and eventually begins to chase after him once Marvin gets close enough and starts speaking.
It is not currently known for sure how the Bacteria originally formed, but it is likely to originate from a mutated strain of Hay bacillus. (See also: Autopsy Report) It (or an entity originating from the same bacteria) makes an appearance at the end of Motion Detected.
- Due to its very stiff legs and hunched posture making it almost reminiscent of a camera tripod, the hunched variation has been aptly-nicknamed "Tripod" by many people.
- Kane Parsons posted a picture of the stick-figure variation on his Ko-fi page, with the caption "Bacteria". This is where the name originally came from.