Introduction Normal flora diverse bacteria colonize our skin and mucous membranes relatively stable flora throughout life effects on the body may be beneficial (e.g., produce nutrients) may be harmful (e.g., cause abscesses or skin and soft tissue infections) no benefit or harm neonates are born sterile but are very rapidly colonized by bacteria after birth sterile areas are areas that do not come into contact with the external environment but can become infected brain and spinal cord lungs blood heart bone Normal Bacterial Flora Site Predominant Bacteria Skin Staphylococcus epidermidis Staphylococcus aureus Propionibacterium acnes Nose Staphylococcus epidermidis Staphylococcus aureus (in some people) Oropharynx Anaerobes Viridans group Streptococcus Streptococcus mutans (grows on biofilms on teeth) Gastrointestinal tract Helicobacter pylori Anaerobes Bacteroides Escherichia coli Urogenital tract Staphylococcus saprophyticus Escherichia coli Group B streptococcus (Streptococcus agalactiae) Lactobacillus