Normal body flora are microorganisms that live on and inside the human body without causing disease. They have a symbiotic relationship with their human hosts, providing benefits like producing vitamins and preventing pathogenic bacteria from growing, while also being provided a habitat. The types of normal flora include resident bacteria that constantly live in one area and transient bacteria that are temporary visitors. Different body sites harbor different normal flora depending on factors like moisture and pH levels. Maintaining a healthy balance of normal flora is important for preventing infection.

1. MUKINGE SCHOOL OF
NURSING
MICROBIOLOGY
HAANTOBOLO A.
BSC. BIOMED. MPH ( C)
MCB 018

2. NORMAL BODY FLORA
• Definition:
• Normal body flora are microorganisms which are
found in specific sites of the body
• Microorganisms that are well established on the
external and internal surfaces of the body
without causing disease

3. Normal flora’s Relationship to the Body
• The normal human body has a profuse normal flora.
• These relationships of micro-organism with the body
may be on the following basis:
• Symbiosis: micro-organisms live harmoniously with
the body (host) and with other micro-organisms.
• Both the body and microorganisms benefit.
• Eg the content of the alimentary canal nourish the
flora living there and in turn the flora synthesise
vitamin K which the body needs (for blood clotting)
but cannot provide for itself.

4. • Commensalism: this is the relation between two
different kinds of organisms when one receives
benefits from the other without damaging it
• Mutualism: The relation between two different
species of organisms that are interdependent;
each gains benefits from the activity of the
other
• Parasitism: The relation between two different
kinds of organisms in which one receives
benefits from the other by causing damage to it
(usually not fatal damage)

5. • Obligatory: this is where the microorganism is
completely dependent on the host
• Antibiosis: An association between organisms
that is harmful to one of them or between
organisms and a metabolic product of another.
• This has led to development of antibiotics.
• An antibiotic is a chemical agent which one
organism produces to inhibit or kill another.

6. TYPES OF NORMAL FLORA
• Resident flora; these are organisms constantly
found in a particulars site of the body e.g
staphylococus aureus which lives on the skin
without causing disease.
• Transient flora; this is non-pathogenic or
potentially pathogenic organism from the
environment.
• They stay on the site from seconds to weeks but
do not produce disease. Eg. Norovirus, which can
cause the stomach flu (viral gastroenteritis)
• Yeast candida

7. • The skin and mucous membrane always harbour
normal floras because they are in contact with
the environment.
• Some body parts have little or no normal flora:
These are:
• The lower respiratory tract. This is facilitated by
micro ciliary bodies that propel organisms to
external surface.
• The stomach due to the production of
hydrochloric acid
• The blood and internal organs-because of
leucocytes (phagocytic action) and physical
separation from external.

8. ELEMENTS THAT ALTER THE GROWTH OF
NORMAL FLORA
• Moisture: it encourages growth of micro-
organisms e.g axilla, between groins, breasts,
testicles, between toes.
• These areas must be kept dry to avoid over
growth of organisms
• Antibiotics; they may kill the normal flora e.g of
the intestine and encourage the growth of other
organisms.
• Antiseptic; regular use of antiseptics (soap)
reduces the bacteria population by more than
95% which can lead to death of normal flora

9. • POSITIVE EFFECTS OF NORMAL FLORA
• Prevent growth of pathogenic organism by means of
competition or antagonism reaction.
• Allows motivation of the immune response
• May induce low antibodies that may cross react with
pathogens.
• NEGATIVE EFFECTS OF NORMAL FLORA
• Normal flora may become opportunistic pathogen
• Some bowel flora acted upon by certain diets may
form carcinogens (cancer causing chemicals)
• Low grade toxaemia due to endotoxin of gastro
intestinal flora is possible
• It may synergise/promote growth of pathogens in
certain areas.

10. BODY SITES AND THEIR NORMAL FLORA
• Micro-flora of the Skin
• The skin has a rich resident of bacteria flora.
• It has 104/cm2.
• The anaerobic predominate in areas with sebaceous
gland in axillae and groin
• Aerobic organisms: staphylococcal epidermidis
• Staphylococcal aureus
• Anaerobic organisms: Propionobacteria
• Klebsella
• Micococci
• Corynebacteria
• Coliform

11. • RESPIRATORY TRACT
• The lower respiratory tract is sterile but the
upper is colonised heavly.
• Dental plague consists almost entirely of
microorganisms
• Nose: - staphylococco epidermidis
• Corynebacteria
• Staphylococco aureus

12. • Oral pharynx :- Streptococco
viridians
•Branhanella
•Corynebacteria
•Bacteroides
•Spirochaetes
•Lacfo bacilli
•Veriolla Actinornyles
•Streptococco pyogens

13. • GASTRO-INTESTINAL TRACT
• The number increase as one moves down the
tract and the flora becomes progressively more
diverse and anaerobic.
• The oesophagus: has a flora similar to that of the
pharynx
• The duodenum, jejunum and upper ileum the
normal flora is scanty
• Large intestine. It is heavily colonised faeces
contain enormous number of bacterium making
up to ⅓ of the weight.
• Many of these are anaerobic. The many bacteria
account for gas that is expelled
•

15. • GENITAL URINARY TRACT:
• For anatomical reasons, the female genital tract is
much more heavily colonised than that of the
male. Normal vaginal secretion contain 108
organism/ml.
• Female:
• Vulva: Staphylococcus epidermidis
• Corynebacteria
• Coliforms
• enterococcus faecalis
• Yeasts

16. • Vagina: Flora of the vagina change with age and
mostly under the influence of oestrogen during
these phases, lacto-bacilli predominate, thus
acting on the glycogen, converting it to lactic
acid.
• This consequently reduce the vaginal PH to 3.8 –
4.7 where as in pre-puberty stage, it is slightly
acidic normal flora include: - Lacto bacilli
• - Coliforms
• - Enterococus faecalis
• - Yeasts
• - Corynebacteria
• - Bacteroides

17. Male and Female
• Urinary bladder:
• Is usually sterile though the distal /anterior
urethra may contain
• Staphylococcal epidermidis
• Corynebacteria

18. • EXTERNAL AUDITORY MEATUS
• Staphylococcal epidermidis
• Corynebacteria
• Acid fast bacteria in the wax- occasionally
• CONJUNCTIVAL SAC
• Microbial population are minimised by the
mechanical flow of tears and presence of
lysozymes organisms include: -
corynebacteria
• -Staphylococcus species