1. Normal Flora in Human Body
DR AMEER MEMON
ASSISTANT PROFESSOR
PHD (ENGLAND)
2. What Are They?
• Normal Flora (indigenous micrbiota) are microbes regularly found at
particular regions of the body
• Resident flora are life-long members present at certain anatomical sites
• Transient microbes are unable to colonize the body for longer periods
• The composition of the normal flora changes with age, sex, diet,
development and environment
3. From Friends to Foe
Opportu
nity
Pathogen
Normal flora
Disease
Happy days
4. The Good, the Bad & the Ugly
Advantages Disadvantages
» prevent colonization by pathogens » can act as opportunistic pathogens
» secrete vitamin K & B12 » gain access to Axenic tissues
» stimulate antibody-mediated » can share nutrients & drug
immune response resistance with pathogens
» inhibit & kill pathogens by » may be a source of infection to
production of enzymes (e.g. other individuals
peroxides, bacteriocins)
6. Axenic Regions of the Body
• Blood vessels
• Brain
• Heart
• Lungs
• Upper urogenital tract (kidneys, ureters, bladder)
Colonization by the normal flora starts at the time of birth and after
7. Normal Flora of the Skin
• Most common sites are: axilla, groin, web spaces
• Staphylococcus epidermidis is the commonest bacterial colonizer which
causes infection via insertion of IV catheters
• Propionibacterium acnes is other common inhabitant of the skin especially
face cause of acne
8. Oral cavity & Upper Respiratory Tract
• Streptococcus mutans is present on the surface of the teeth cavities
• The nose is colonized by a potential pathogen, Staphylococcus aureus
especially in hospital staff. Major cause of surgical wounds
• Streptococcus pneumoniae resides in the mouth and throat. Commonest cause
of bacterial pneumonia
• Streptococcus pyogenes, Neisseria species colonize the pharynx
9. Gastrointestinal Tract
• Stomach has a highly acidic pH however Helicobacter pylori can survive there
• Enterococcus faecalis, E. coli and Bacteroids are mainly in the small intestine
• Bacteroids and Bifidobacterium are predominant flora in the large intestine
(colon). Clostridium species are also regularly found
• Bifidobacterium preparations are available in the market (e.g. in yoghurts)
knows as “Probiotics”
• Clostridium difficle (Super bug) is the cause of severe diarrhea-associated
colitis called “pseudomembraous colitis”
10. Urogenital Tract
• Anterior urethra - Staph. epidermidis
Streptococcus viridans
E. coli, Proteus
• Vagina - Lactobacillus in adults has a protective role against certain
pathogens
Staph. epidermidis
Neisseria species
Streptococcus agalactiae
