Bacteria
As we all learned in a school, there are several sorts of bacteria, and not all of them as the same as each other. Some are caught from semen and the rest are caught from feelthy humans.
E coli
This bacterium is found in sandwiches and Scotland. Its first name begins with the letter "E" and it looks shifty down a microscope.
Bacterium Toiletseat-icans
This bacterium is caught by ladies from toilets which have had the seat left up by gentlemen. It is probably fatal.
Bacterium Dosmestos-icum
This bacterium is the 1% percent of household germs that household cleaning bleach Domestos cannot kill. It's a bit like AIDS, but smaller, and it preys on OCD.
Flying toilet germs
The official scientific name of a new breed of horror that takes to the air in a toilet-shaped helicopter gunship and delivers mighty vengeance on those who don't wash their hands. [1][2]
Giant Bacteria
In the Doctor Who episode Raiders Of The Lost Ark ... IN SPACE! the large green things the size of a Golden Retriever seen during the show were actually Macrobacter [3]. The fact they they looked like stunt men wrapped in green carpet sliding along the linoleum in BBC Studio B, Shepherd's Bush [4] only added to the unworldly terror.
The bacteria who killed the Martians
Tom Cruise and John Travolta saved the earth from the Marcab Confederacy in War Of The Worlds. Probably.
The cancer that is making /b/ cough a bit
Man flu. Almost certainly.
Syphilis and MRSA
These are technically germs and should be ignored.
The Black Death
According to Wikipedia, this gives you bubos, which is Greek for owls [5]. Hence the expression "This bubonic plaque is a total hoot." (Joke copyright; Ingmar Bergmann [6].) Deleted due to factual inaccuracy.
Computer bacteria
A computer bacteria is a computer program that can reproduce by binary fission and infect a computer. The Satan Bug [7] was first detected on televisions, the forerunner of the Internet, in the early 1970s, whilst a program called "Emergency Moonbase Alpha" was the first computer bacteria to appear "in the wild", feeding on lions or something. Computer bacteria attach themselves to the Apple DOS 3.3 operating system and spread via floppy disk, so no iPad is safe [8].