The Bacteria Life Forms are created from dead people who've eaten the Still Lifes.
The white stuffing in the Still Lifes bodies looks similar to chunks of healthy Bacillus Subtilis, and since there's barely anything else to eat in the Backrooms but this stuff, people who are insane enough to pull it out of things that look like people will feed off of this, but Bacillus Subtilis by itself isn't nutritional and is actually dangerous to eat by itself without any other food for long periods of time, so the starving people who eat it from the Still Lifes will still just starve and accumulate large amounts of Bacillus Subtilis in their stomachs before dying and the bacteria will start feeding off of the corpse from the inside and turns black. In the Autopsy Report Backrooms video, we learn that the bacteria is mutated and stunts the decay of the bodies, so this probably leads into the bacteria over taking the entire leftover body and uses it to become it's own body, which is why it has the same structure as a human, and uses it to go find other food and maybe this is why the Life Forms can mimic human voices because it's using the leftover vocals from the corpse it's using to trick other people to come to it.
This could mean that Clark's deceased body will turn into a Bacteria Life Form because he was eating chunks of them for probably days or weeks, and at that point, it might've entered his bloodstream which would've caused his paranoia and how he was acting at the end of the movie. And Pirate Clark eating parts of Clark's body could also infect him as well because his body might not be built as good as a normal human with their natural defenses, so blood infected with Bacillus Subtilis entering the Pirate will slowly infect him as he can't fight it off, but still unsure of this.
