Normal Flora of Human Body, Skin, Respiratory Tract, Intestinal tract, Genitourinary tract, Eye

There are some species of bacteria and fungi that are a permanent resident of specific sites of our body. Bacteria and fungi are included in the normal flora, viruses and parasites are not a part of normal flora.
These bacteria and fungi which are normal and permanent residents of specific sites of our body, don’t usually cause the disease, but they may cause disease in certain situations. Usually, they protect us from diseases by competing with the disease-causing bacteria for space and food.

Normal Flora of Human Body

Normal Flora of Skin

The following bacteria and fungi are part of normal and permanent inhabitants of the skin

1. Staphylococcus epidermidis
2. Staphylococcus aureus
3. Corynebacterium diphtheria
4. Group G streptococci
5. Pseudomonas aeruginosa
6. Peptococcus
7. Candida albicans (fungi)

Normal flora of Respiratory Tract

• Nose: Staphylococcus aureus, Staphylococcus epidermidis, Corynebacterium diphtheria, and other streptococci are the part of the normal flora of nose.
• Throat, Larynx & Trachea: Viridans streptococci, Streptococcus pyogenes, Streptococcus pneumoniae, Neisseria species, Haemophilus influenzae, Staphylococcus epidermidis are permanent residents of the respiratory tract.

Normal Flora of the Oral Cavity

• Mouth: Viridans streptococci and other species of streptococci.
• Dental Plaque: Streptococcus mutans
• Gingival Cervices: Bacteriodes, Fusobacterium, Streptococci, Actinomyces

Normal Flora of Intestinal Tract

• Small intestine: Enterococci, Lactobacilli, Staphylococci, Candida albicans.
• Colon: Bacteroides, especially bacteroides fragilis, Escherichia coli, Enterobacter, Serratia, Pseudomonas aeruginosa, Bifidobacterium, Fusobacterium, Lactobacillus, Enterococci especially E. faecalis, Non-enterococci, especially S bovis, Streptococcus anginosus, Clostridium especially perfringens.

Normal Flora of Genitourinary Tract

• Vagina: Lactobacillus, Streptococcus agalactiae, Streptococcus anginosus, Various Gram-negative rods, B. fragilis, Corynebacterium and Candida albicans
• Urethra: Staphylococcus epidermidis, Corynebacterium diphtheria, Various streptococci, Various Gram-negative rods and Mycoplasmas
• External Genitalia: Mycobacterium smegmatis

Normal Flora of Eye

1. Corynebacterium xerosis
2. Staphylococcus aureus
3. Staphylococcus epidermidis

You can clearly see that in the above list certain bacteria are known to cause serious diseases, such as E. coli, Staphylococcus aureus, S. pneumonia and many others, but remember that there are present in a balanced number. If the number of any of the above bacteria increases due to any cause, then these may cause disease. For example, Clostridium difficile is present in small numbers in the colon, but after long term antibiotic use that kills a large number of bacteria other than Clostridium difficile, cause a serious disease called pseudomembranous colitis due to over-growth of clostridium difficile. Therefore, if the bacteria are present in a balanced number then they all are friendly bacteria.