The document details the normal microbial flora that inhabit the human body, categorizing them into resident and transient flora. It discusses the advantages of this flora, such as production of vitamins and immune support, as well as disadvantages where they can become pathogenic under certain conditions. Various microorganisms are identified across different body regions, including the skin, mouth, gastrointestinal tract, and genitalia.

1. NORMAL MICROBIAL FLORA OF
HUMAN BODY
C.SWAMINATHAN
Assistant Professor of Microbiology
Vivekanandha College of Arts and Sciences
(Autonomous) for Women
Tiruchengode – 637 205
Tamilnadu, South India

2. The term ‘normal flora’ denotes the population of
microorganisms that inhabit the skin and mucous
membrane of normal healthy individuals
1) Resident Flora:
Constitute a constant population
Cannot be removed completely
2) Transient Flora:
Consists of non-pathogenic or potentially
pathogenic microbes
Derived from the environment
Inhabit the skin or mucous membrane for hours,
days or weeks

3. ROLE OF NORMAL MICROBIAL
FLORAAdvantages
They prevent or suppress the entry of pathogens
Produce vitamin K and vitamin B
Raise the overall immune status of the host
against pathogens having related or shared
antigens
The antibiotic substance produced by some, for
example, colicins have a harmful effect on
pathogens
Endotoxins liberated by normal flora may help the
defence mechanism of the body

4. Disadvantages
They become pathogenic when the immunity is
lowered
Act as pathogens in tissues outside their habitat.
e.g. normal flora of intestine may cause UTI
Cause confusion in diagnosis due to their
ubiquitous presence and their resemblance to some
of the pathogens

5. SKIN
Staphylococcus epidermidis
Staphylococcus hominis
Staphylococcus haemolyticus
Staphylococcus capitis
Streptococcus pyogenes
Micrococcus luteus
Corynebacterium xerosis
Peptostreptococcus spp
Propionibacterium spp
Clostridium perfringens
Candida albicans
Malassezia furfur

6. CONJUNCTIVA
Relatively free from
microorganisms due to the
flushing action of tears and
presence of lysozyme in tears
Corynebacterium xerosis
Moraxella spp
Staphylococcus spp
Non haemolytic Streptococci

7. NOSE, NASOPHARYNX AND
SINUSES
Corynebacterium spp
Staphylococcus spp
Streptococcus spp
Haemophilus spp
Moraxella lacunata
P.aeruginosa, E.coli, Proteus spp –
occasionally found

8. MOUTH AND UPPER RESPIRATORY
TRACTMouth
Pigmented and non pigmented
micrococci
Gram+ aerobic spore bearing bacilli
Coliforms, Proteus, Lactobacilli
Gum pockets and Tonsils
Anaerobic micrococci, Anaerobic
streptococci
Vibrios, Fusiform bacilli,
Corynebacterium spp
Actinomyces, Mycoplasma
Neisseria, Bacteroides

9. GASTROINTESTINAL TRACT
GI of foetus is sterile. It becomes
contaminated with organism shortly
after birth
Breast fed children
Lactobacillus bifidus
Enterococci
Colon bacilli
Staphylococci
Bottle fed children
Lactobacillus acidophilus
Enterococci
Colon bacilli

10. Stomach – pH is low – sterile
Small intestine
Lactobacilli
Streptococci
Enterobacteria
Bacteroides
Large intestine
Anaerobic streptococci
Anaerobic lactobacilli
Clostridium spp, Bacteroides
spp,
Coliforms
Enterococci
Proteus
Pseudomonas
Candida

11. GENITOURINARY TRACT
M.smegmatis – genitalia of male
and female
Microflora of genitalia of men
Lactobacilli
Gardnerella vaginalis
Alpha haemolytic streptococci
Bacteroides spp
Chlamydia trachomatis
Ureaplasma urealyticum
Microflora of vagina
Lactobacilli, Bifidobacterium
Peptostreptococcus,
Propionibacterium
Staphylococcus, Streptococcus
Corynebacterium, Neisseria,
Haemophilus,
Enterobacteriaceae
Non pathogenic Treponema
Candida spp