ABSTRACT
In a clinical situation, bacteria and viruses are by far the most common causative agents of human diseases. The bacteria are single-celled organisms with both DNA and RNA (which contrasts them with viruses). Unlike eukarya, the chromosomes of bacteria are not enclosed within a nuclear membrane and they have no membrane-bound organelles such as mitochondria, Golgi apparatus or endoplasmic reticulum. A cell wall is usually present which may possess appendages such as pili, fimbriae and flagella. At the simplest level bacteria can be divided into groups depending on their staining characteristics and their morphology, although biochemical, molecular and genetic techniques are also applied.
