According to my medical source (Mrs.MPL) when considering bacteria the majority are made up of four main 'Gram' comprised of positive cocci, negative cocci, positive bacilli and negative bacilli-types and these are categorised by the type of cell wall they have and their overall shape.
The three other types are pirochaetes, which has three distinct species of its own, treponema, leptospira and borrelia all of which cause a number of diseases.
Then rickettsia that is often responsible for typhus but can only survive inside a host cell.
And mycoplasma which have no cell wall which can cause pneumonia.
But then you have all the viruses that constantly mutate, fungal spores and a variety of tiny invertebrate creatures such as protozoa.
As Mr.S so eloquently puts it "lots".... ?