An especially grim group, the filamentous viruses, includes the deadly Ebola and Marburg viruses. But don't feel discriminated against just because you're a primate. Other viruses are designed to attack plants, fungi, even bacteria. Generally, bacterial cells are contained by a rigid cell wall and a rubbery membrane. Inside, the DNA is loose rather than contained within a nuclear membrane, as it is in all other forms of life.
Bacteria are much larger than viruses, and like any adult, have more responsibilities.
Bacterial infections include sweethearts like Staphylococci, Streptococci, anthrax, botulism and cholera. But bacteria are not all nasty. Your intestines are crammed with E. coli bacteria, which help you digest your food, and bacteria help in many ecological processes. More on disease bacteria . Like viruses and bacteria, parasites live at the expense of other organisms.