1. Microflora of the human body
bacteria and immunity system
Zuzana Čermáková, D.V.M., Ph.D.
Institute of clinical microbiology
Tel. 606 718 562, 495 833 540,
E-mail: cermakovaz@fnhk.cz

2. Importance in human health
Human digestion
Microorganisms can form an endosymbiotic
relationship with other, larger organisms. For
example, the bacteria that live within the human
digestive system contribute to gut immunity
(immunoglobulins A class above all), synthesise
vitamins such as folic acid and biotin, vitamine B
complex and ferment complex indigestible
carbohydrates.
Microorganisms are on the skin, in the mouth, in the
upper respiratory tract....... = and forms normal
microflora of human body – prevention of pathogens

3. Human flora
The human flora are the microorganisms that
constantly inhabit the human body
• They include bacteria, fungi and archea.
• Some of these organisms are known to perform
tasks that are useful for the human host, while the
majority have no known beneficial or harmful effect
•Those that are expected to be present, and that
under normal circumstances do not cause disease,
are termed normal flora, or microbiota.

4. It is estimated that 500 to 1000 species of bacteria
ive in the human body
Though normal flora are found on all surfaces
exposed to the environment (on the skin and eyes, in
he mouth, nose, small intestine), the vast majority of
bacteria live in the large intestine
Many of the bacteria in the digestive tract,
collectively referred to as gut flora, are able to break
down certain nutrients such as carbohydrates

5. The majority of these commensal bacteria are
anaerobes, meaning they survive in an environment
with no oxygen (GIT).
Bacteria of the normal flora can act as opportunistic
pathogens at times of lowered immunity
Escherichia coli is a bacterium that lives in the
colon; it is an extensively studied model organism
model organism and probably the best understood
bacterium of all
Certain mutated strains of these gut bacteria do
cause disease; an example is E.coli O157:H7

6. Normal flora

is the mixture of organisms regularly found at
any anatomical site (skin, GIT, vagine…)
Composition of normal flora depends upon many
various factors: - genetics, age, sex, stress,
nutrition, diet…
Mutualistic relationship: The normal flora derives
from the host a supply of nutrients, a stable
environment, constant temperature, protection
and transport. The host obtains from the normal

7. …flora certain nutritional benefits, stimulation of the
mmune system, and colonization strategies that
exclude potential pathogens at the site.
site
members of the normal flora are normaly adapted to
heir host /tissues/, most probably by biochimical
nteractions between bacterial surface components
ligands or adhesins) and host cell molecular
eceptors
The explanations for why the normal bacterial flora
are located at paticular anatomical sites are
practically three:

8. Tissue tropism – one explanation of tissue
tropism is that the host provides an essential
growth factor needed by the bacterium, on the
oposite site the host produses in other organs
stomach acids, bile salts, lysozym….and this
sites are not favourable for live organisms…
Many of the normal flora are able to specifically
colonize a particular tissue or surface using their
own surface components like capsules, fimbriae,
cell wall components, as specific ligands for
attachment to specific receptors located at the
colonization sites

9. 3) Some of the indigenous bacteria are able to
construct bacterial biofilms on a tissue surface
Many biofilms are a mixture of microbes, although
one member is responsible for maintaining the
biofilm and may predominate

10. The composition of the normal flora
It has been calculated that the normal human is
host to about 1012 bacteria on the skin, 1010 in the
mouth and 1014 in the gastrointestinal tract
Normal flora of the skin
An adult person is covered approximately with 2
square meters fo skin
The density and composition of the normal flora of the
skin vary with anatomical locale
Ex. the high moisture of content of the axilla…..is
good place for „cultivation“ of bacteria and fungi
(relatively high density of bacterial cells)

11. …but at most other sites the bacterial population is
airly low – generally cells, generally 100 – 1000 per
square cm
the majority of skin microorganisms are found in the
most superficial layers of the epidermis and the upper
parts of the hair follicles
Staphylococcus epidermidis, Micrococcus spp.,
nonpathogenic corynebacteria
their are generally nonpathogenic – commensals, or
mutualists (in immunocompetent persons)
persons
Skin bacteria or their metabolites may protect
against colonization by dermatophytic fungi or
pathogenic bacteria

12. sometimes potentially pathogenic
Staphylococcus aureus is found on the face and
hands, particularly in individuals who are nasal
carriers
3. Normal flora of the respiratory tract
The nares (nostrils) are always heavily colonized,
predominantly with Staphylococcus epidemidis
and corynebacteria (about 20% of the general
population) with Staphylococcus aureus (also
MRSA carriers),
Sinuses (healthy) – are sterile (in normal
conditions)

13. The upper respiratory tract (nasopharynx) –
predominantly non-hemolytic and alphahemolytic
streptococci and Neisseria species and
sometimes pathogens such as Str.pneumoniae,
Haemophilus influenzae, Neiseria meningitidis.
Lower respiratory tract (trachea, bronchi,
pulmonary tissues) – are uppon the normal
conditions free of microorganisms – mainly
because of the efficient cleansing action of the
ciliated epithelium which covers respiratory tract
Any bacteria reaching the lower respiratory tract are
removed by the action of this epithelia and also by
coughing, sneezing, swallowing, etc…

16. 3. Normal flora of the Human Oral Cavity
Streptococci, lactobacilli, staphylococci and
corynebacteria (aerobic, microaerophiles) and
anaerobes ( bacteroides
**********
The mouth presents of different ecological situations
with age, and this corresponds with changes in the
composition of the normal flora (good example of
mportance of bacteria for immunity system):
At birth the oral cavity is composed of the soft
issues (lips, cheeks, tongue, palate…) which are kept
moist by the secretions of the salivary glands

17. • at birth the oral cavity is sterile but rapidly
becomes colonized from the environment,
particularly from the mother in the first feeding and
then in other contact with mother – hands, lips…..
• Streptococcus salivarius is dominant – 98% of the
total oral flora until appearance of the teeth (6-9
months in humans)
• S. mutans, S. sanguis…..
• In contact with healthy adults young children are
colonized with other bacteria – Staphylococcus
epidermidis, Escherichia coli, nonpathogenic
corynebacteria and immunity system starts „the
training“
• Immunity system develops in children organism to
5 years of age

18. 4. Normal flora of conjunctiva
a variety of bacteria may be cultivated from the
normal conjunctiva but the number of organisms is
usually small (S.epidermidis, nonpathogenic
corynebacteria, Propionibacterium acnes) are
dominant
S.aureus, streptococcus spp., Haemophilus spp.,
Neisseria spp. are occasionally found
The conjunctiva is kept moist (tears = lachrymal
secretion with lysozyme)
Pathogens usually are: Chlamydia trachomatis,
S.aureus, Neisseria gonnorhoae, streptococci,
enterococci….

19. 5. Normal flora of the Urogenital Tract
Urine is normally sterile
Lower parts of urethra may be colonized with a
small density of nonpathogenic S.epidermidis,
streptococcus spp. – alfa-hemolytic, enterococci,
corynebacteria
pathogenic bacteria – in urogenital system which
can cause infection and inflammation may be:
Gramnegative rods (Proteus spp., E.coli),
Streptococcus B group (agalactiae), enterococci….
about 80-90% infections of the urinary tract -
woman – short distance from anus – source of
bacteria

20. 6. The vagine
Normaly is colonized corynebacteria, nonpathogenic
streptococci, staphylococci – nonpathogenic, small
number of yeasts – Candida albicans and very
mportant is Lactobacillus acidophilus (named
Döderlein´s bacillus) – lower pH !!! – prevention
against pathogenic flora (and also Trichomonas
vaginalis)
Pathogens: Neisseria gonorrhoae, Str. agalactiae,
gram-negative rods – E.coli, Proteus spp., yeasts,

21. 7. Normal flora of the gastrointestinal tract
GIT)
E. coli, other gram-negative rods – nonpathogenic
Klebsiella spp., Proteus spp.,), Enterococcus, other
streptococci, anaerobic bacteria – Clostridia, Bacillus
spp., Bacteroides……
And many nonpathogenic protozoa, yeasts
Ex. Pathogens: Salmonella spp., Shigella spp.,
pathogenic E.coli, Helicobacter pylori, Campylobacter
ejunii…rotaviruses….parasites: Entamoeba
histolytica (protozoon), wormes ……

22. Benefits of the normal intestinal human flora
synthesis and excretions of vitamins (B group),
vitamin K (E.coli)
prevent colonization by pathogens by competing
or attachment sites or for essential nutrients
the normal flora also produces substances which
nhibit or kill nonindigenous species (pathogens)
The normal flora in general stimulates the
development of certain lymphatic tissues – parts of
mmunity system in GIT
The normal flora – in general – stimulate the
production of cross-reactive antibodies.

23. It is known that the normal flora induce
mmunological responses
very low level usually non-specific antibodies
cross-reactive) react with certain related pathogens
and can prevent infection or invasion
„training“ of the immunity system by contact
with normal flora is very important and it is
condition for normla surviving of
macroorganisms (animals, human) in the
normal environment