Presence of Normal Flora in the Body​

• Locations where Normal Flora can be found


  • Skin
  • Eyes (Conjunctiva)
  • Nose (Respiratory tract)
  • Mouth (Oral Cavity)
  • Ears
  • Genitourinary tract
  • Alimentary canal
• Important sites for Normal Flora on the Skin

  • Axilla
  • Groin
  • Areas between the toes
• Skin


  • Can acquire any transient bacteria from the environment but it either get washed off or die because the skin is dry, has acidic pH, and produce sweat and oil
  • Resident bacteria of the skin can be in any layer of the skin
  • The skin is generally a dry, acid environment that does not support the growth of most microorganisms
  • Moist areas (e.g., sweat glands) are readily colonized by gram-positive bacteria and other normal flora of the skin
• Factors influencing the composition of Normal Flora on the Skin


  • Environmental factors (e.g., weather)
  • Host factors (e.g., age, personal hygiene)
• Staphylococcus epidermidis


  The most abundant inhabitant of the skin, especially the upper body
• Staphylococcus aureus


  • The nose is one of the most common sites for S. aureus
  • It is a leading cause of bacterial disease in humans
  • It can be transmitted from the nasal membranes of a carrier to a susceptible host (immunocompromised)
• Propionibacterium acnes


  • Located on greasy areas of the skin, such as the forehead
  • Can become trapped in hair follicles and cause inflammation and acne
  • Different species of Propionibacterium can live on the sides of our nose and on our armpits
• Types of Normal Flora on the Skin

  • Aerobic Bacteria (Staphylococcus epidermidis (accounts 90%) + Staphylococcus aureus)
  • Anaerobic Bacteria (Propionibacterium acnes)
• Skin normal flora are generally harmless but it might cause bloodstream infections if skin was penetrated
• Important bacteria in the Normal Flora of the Skin

  • Staphylococcus epidermidis
  • Micrococcus Species
  • Corynebacteria species
  • Mycobacterium smegmatis
• Normal Flora of the Conjunctiva

  • Staphylococcus epidermidis
  • Corynebacterium sp.
  • Propoinibacterium acnes
  • Staphylococcus aureus
  • Viridans streptococci
  • Neisseria sp.
  • Haemophilus influenzae
• Tears (Lysozyme enzyme), mucus, and oil will protect the conjunctiva of the eye from colonization by more bacteria
• Pathogens which do infect the conjunctiva

  • Neisseria gonorrhoeae
  • Chlamydia trachomatis
• Normal Flora of the Nasal Cavity

  • Staphylococcus epidermidis
  • Corynebacteria
  • Staphylococcus aureus
  • Neisseria sp.
  • Haemophilus sp
  • Streptococcus pneumoniae
• Normal Flora of the Upper Respiratory Tract (Nasopharynx)

  • Non-hemolytic streptococci
  • Alpha-hemolytic streptococci
  • Neisseria sp.
  • Streptococcus pneumoniae
  • Streptococcus pyogenes
  • Haemophilus influenzae
  • Neisseria meningitidis
• The lower respiratory tract (trachea, bronchi, and pulmonary tissues) is usually sterile
• The individual may become susceptible to infection by pathogens descending from the nasopharynx e.g. H. influenzae and S. pneumoniae
• Normal Flora of the Oral Cavity

  • Viridans streptococci
  • Lactobacilli
  • Staphylococci (S. aureus and S. epidermidis)
  • Corynebacterium sp.
  • Bacteroides sp.
  • Streptococcus sanguis (dental plaque)
  • Streptococcus mutans (dental plaque)
  • Actinomyces species
• The oral cavity has both aerobic and anaerobic bacteria, with the most common ones being C. diphtheroides, S. aureus, and S. epidermidis
• The oral cavity can also contain yeasts, molds, protozoa, and viruses
• Streptococcus mutans


  Found in the teeth and gingiva
• Poor dental hygiene helps bacteria to grow and cause dental caries, gingivitis, etc.
• After dental surgeries, there might be a risk of bloodstream infection that might cause endocarditis
• Normal Flora of the External Ear

  • Staphylococcus epidermidis
  • Staphylococcus aureus
  • Corynebacterium sp
• The middle ear and inner ear are usually sterile
• The outer ear and the auditory canal contain the same normal flora of the skin
• When the person coughs, sneezes, or blows his nose, these microbes may move into the middle ear where they cause infection
• The kidneys, ureters and urinary bladder are sterile
• Normal Flora of the Lower Urethra and External Opening

  • Bacteria, yeast, and viruses (same as skin)
• Normal Flora of the Vagina

  • Lactobacillus spp.
  • Corynebacterium sp.
  • Staphylococci
  • Nonpyogenic streptococci
  • Escherichia coli
  • Flavobacterium sp.
  • Clostridium sp.
  • Viridans streptococci
  • Other Enterobacteria
• Lactobacillus spp. keeps the vaginal pH acidic to protect the vagina from opportunistic infections e.g. fungal vaginitis (Candida albicans) or bacterial vaginosis (Bacteroides spp., Gardnerella vaginalis)
• Imbalances in the normal vaginal flora can be caused by high levels of estrogen (e.g. pregnancy), use of broad-spectrum antibiotics, and certain birth control pills
• Normal Flora of the Anterior Urethra

  • Staphylococcus epidermidis
  • Enterococcus faecalis
  • Alpha-hemolytic streptococci
  • Some enteric bacteria (e.g. E. coli, Proteus sp.)
  • Corynebacteria species
  • Acinetobacter species
  • Mycoplasma species
  • Candida species
  • Mycobacterium smegmatis
• Factors influencing the Normal Flora of the Gastrointestinal Tract

  • Age
  • Diet
  • Cultural conditions
  • The use of antibiotics
• Normal Flora of the Gastrointestinal Tract in Breastfed Infants

  • Bifidobacteria (account for more than 90% of the total intestinal bacteria)
  • Enterobacteriaceae
  • Enterococci
  • Bacteroides
  • Staphylococci
  • Lactobacilli
  • Clostridia
• Normal Flora of the Gastrointestinal Tract in Bottle-Fed Infants


  • Enterics
  • Bacteroides
  • Enterococci
  • Lactobacilli
  • Clostridia
• Normal Flora of the Upper Gastrointestinal Tract in Adults

  • Acid-tolerant lactobacilli
• Normal Flora of the Proximal Small Intestine in Adults

  • Lactobacilli
  • Enterococcus faecalis
  • Coliforms
  • Bacteroides
• The stomach contains fewer bacteria due to its high acidity nature, e.g. Helicobacter pylori
• Normal Flora of the Large Intestine

  • Anaerobic Bacteroides spp. (99% of normal flora)
  • Fungi
  • Protozoa
  • Viruses