infectious diseases
Overview of Bacteria
Introduction
 species, and rickettsiae. Facultative intracellular pathogens are able to live and reproduce either inside or outside of host cells. Examples of these pathogens include Overview of Salmonella Infections , Many bacteria are present in humans as normal microbiota, often in large numbers and in many areas (eg, in the gastrointestinal tract and skin). Only a few bacterial species are human pathogens. Bacteria are classified by the following criteria (see also table Classification of Common Pathogenic Bacteria ): Morphology Staining Encapsulation Oxygen requirements 