Indigenous (Normal) Flora
The indigenous flora (microflora; microbiota) includes all the, microorganisms that are normally found on or in the body – they inhabit body surfaces, skin and mucous surfaces with direct access to the external environment. The normal flora is not static – it is composed of resident organisms, transient organisms and replacement organisms. Most of them are commensals – some are potential pathogens. From birth the body becomes progressively colonised with normal flora (the foetus has no indigenous flora).
Human body is thought to harbour over 1014 with over 500 species.
Benefit of normal flora keep immune system being stimulated; provide some essential nutrients; prevent pathogenic organism becoming established (competition for food, pH levels, oxygen levels, antibiotic production); nutrition (eg synthesis of vitamin K by E. coli)
Main organisms that comprise the skin flora include staphylococcus epidermidis, Propionibacterium acnes, anaerobic cocci, micrococci, corynebacteria. Less commonly there are coliforms and staphylococcus aureus (this potential pathogen is present in 50% of population).
Normal flora of nose include staphylococcus epidermidis, staphylococcus aureus, corynebacteria.
Common organisms in normal flora of large intestine include Bacteriodes, Bifodobacteria, anaerobic cocci, E. coli, Enterococcus faecalis, Clostrida, Lactobacilli.
Normal flora of foot -
Potential pathogens in normal flora become pathogenic if they:
1) Reach an abnormal site (eg invasive surgical procedure; skin is breached – wounds, burns, water soaked hands)
2) Imbalance in flora (eg use of antibiotics)
3) Change in immune status of host (eg age; disease)
Need to consider normal flora when interpreting results of laboratory specimens; use of antibiotics; disinfection of skin prior to invasive surgery; understanding how infection can develop in the immunocompromised.