inform about normal flora

2. Normal human
flora
Dr.R.B.Y(MBBS<Running>)
2

3. Human microbiome
• The human microbiome (or human micro biota) is the aggregate
of microorganisms that reside on the surface and in deep layers of
skin, in the saliva and oral mucosa, in the conjunctiva, and in the
gastrointestinal tracts. They include bacteria, fungi. Some of these
organisms perform tasks that are useful for the human host.
However, 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, but instead participate in
maintaining health, are deemed members of the normal
flora
Dr.T.V.Rao MD
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4. Normal bacterial Flora
• More bacterial than
human cells in the
body
provi•de some nutrients (vitamin K)
stimu• late immune system,
immunity can be
cross-reactive against certain
pathogens
Preve• nt colonization by potential
pathogens
(antibiotic-associated colitis,
Clostridium difficile)
Dr.T.V.Rao MD
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5. Overview of Human-Microbial Interactions
• Microbial flora of the healthy human host
1) The reasons for understanding the normal flora of the healthy human
body
Normal flora ▶ vs. human body
▶ Some normal flora: opportunistic pathogens
Dr.T.V.Rao MD
when injury occurred,
when resistance of body decreased,
when moved to another site
2) Origin of the normal flora
3) Relationship between normal flora and human host
4) Distribution and occurrence of the normal flora
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6. Where to find microbe?
Everywhere!
Dr.T.V.Rao MD 6

7. Introduction of Normal Flora
1 . A diverse microbial flora =>
• Human body Area: the skin and mucous membranes
• Time: shortly after birth until death
• Number: 1014 bacteria =>1013 host cells
• 2. Normal flora may:
• a. Aid the host
• b. Harm the host (in sometimes)
• c. Exist as commensals (no effect to the host)
3. Viruses and parasites => NOT normal microbial flora
• Most investigators consider that they are not commensals and do not aid
the host.
Dr.T.V.Rao MD
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8. Normal Flora and Pathogenesis
Outcomes of exposure to a microorganism:
1. Transient colonization
2. Permanent colonization
3. Disease
Colonization vs. Infection
Colonization: establishment of a site of reproduction of
microbes on a person without necessarily resulting in
tissue invasion or damage.
Infection: growth and multiplication of a microbe in or on
the body of the host with or without the production of
disease.
Dr.T.V.Rao MD
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9. Significance of Normal Flora
• 1.The normal flora influences the anatomy, physiology, susceptibility to
pathogens, and morbidity of the host.
• 2. The effect of the normal flora on the host was not well
• understood until germ-free animals became available.
• Cesarean Section => Germ-free animals => Isolators w/o detectable
pathogens (viruses, bacteria & others)
• 3. Two interesting observations:
• a. the germ-free animals lived almost twice as long as their
conventionally maintained counterparts.
• b. the major causes of death were different in the
• two groups.
Dr.T.V.Rao MD
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10. Factors Influencing Normal Flora
1. Local Environment (pH,
temperature, redox
potential, O2, H2O, and
nutrient levels…).
2. Diet
3. Age
4. Health condition (immune
activity…)
5. Antibiotics,…..etc
Dr.T.V.Rao MD
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11. Significance of Normal Flora
Normal flora may aid the host in several ways:
• Aid in digestion of food
• Help the development of mucosa immunity
• Protect the host from colonization with
pathogenic microbes.
Dr.T.V.Rao MD
106
pathogenic
microbes
GI infection
w/ normal flora
GI infection
10 pathogenic
microbes
w/ reduced flora after
Streptomycin treatment
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12. Composition of the Normal Flora
• The normal flora of humans are exceedingly complex and consist of more
than 200 species of bacteria. The makeup of the normal flora may be
influenced by various factors, including genetics, age, sex, stress,
nutrition and diet of the individual.
Three developmental changes in humans, weaning, the eruption of the
teeth, and the onset and cessation of ovarian functions, invariably affect
the composition of the normal flora in the intestinal tract, the oral cavity,
and the vagina, respectively. However, within the limits of these
fluctuations, the bacterial flora of humans is sufficiently constant to a give
general description of the situation
Dr.T.V.Rao MD
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13. Dr.T.V.Rao MD 13

14. When we get colonized with Normal
• A human first becomes colonized
by a normal flora at the moment of
birth and passage through the birth
canal. In utero, the fetus is sterile,
but when the mother's water breaks
and the birth process begins, so
does colonization of the body
surfaces. Handling and feeding of
the infant after birth leads to
establishment of a stable normal
flora on the skin, oral cavity and
intestinal tract in about 48 hours.
Dr.T.V.Rao MD
Flora
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15. A new born child's flora is dependent on
Dr.T.V.Rao MD
mother
• The composition of a
child’s bacterial flora
is dependent on the
mother’s micro flora,
since she is the
primary source for
the child’s bacteria at
the outset
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16. Density of normal flora in Humans
Dr.T.V.Rao MD
• It has been calculated that a
human adult houses about 1012
bacteria on the skin, 1010 in the
mouth, and 1014 in the
gastrointestinal tract. The latter
number is far in excess of the
number of eukaryotic cells in all
the tissues and organs which
comprise a human. The
predominant bacteria on the
surfaces of the human body are
listed in Table 3. Informal names
identify the bacteria in this table.
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17. • Resident flora
•Reflects sex
of person
Dr.T.V.Rao MD
Normal Flora
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18. Potential colonization sites
Dr.T.V.Rao MD
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19. Dr.T.V.Rao MD
Humans as Habitats
• Colonization (and infection) frequently begin at mucous
membranes
•These are found throughout the body. Consist of single or multiple layers of
epithelial cells, tightly packed cells in direct contact with the external
_____________________________.
Bacteria may
associate loosely
or firmly
Breaches in the
______________
_ barrier can
result in infection
(pathogenesis)by
opportunistic
path1o9gens

20. Upper respiratory tract – and
Lower Respiratory tract
Dr.T.V.Rao MD
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21. Common Skin Bacterium May Be New
Dr.T.V.Rao MD
Opportunistic Pathogen*
•Helococcus kunzii is a recently identified bacterium that is thought to
be a nonpathogenic member of normal human skin flora and is rarely
associated with skin infections. In the study though, the researchers
report the isolation of the organism from an infected cyst on the
breast of a 57-year-old immunocompromised woman.
• Finding provides further support for the opportunistic role of
H. kunzii in causing infection in both immunosuppressed and
immunocompetent patients," say the researchers.
•A.H. Chagla, A.A. Borczyk, R.R. Facklam, and M. Lovgren. 1998. Breast abscess associated with Helocococcus kunzii. Journal of
Clinical Microbiology. 36:2377-2379.)
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22. Associations Between Humans and the Normal
Dr.T.V.Rao MD
Flora
• E. coli is the best known bacterium
that regularly associates itself with
humans, being an invariable
component of the human intestinal
tract. Even though E. coli is the
most studied of all bacteria, and
we know the exact location and
sequence of 4,288 genes on its
chromosome, we do not fully
understand its ecological
relationship with humans
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23. commensal relationship.
• Sometimes the relationship between a
member of the normal flora an its host cannot
be deciphered. Such a relationship where
there is no apparent benefit or harm to either
organism during their association is referred
to as a commensal relationship.
Many of the normal flora that are not
predominant in their habitat, even though
always present in low numbers, are thought of
as commensal bacteria. However, if a
presumed commensal relationship is studied
in detail, parasitic or mutualistic
characteristics often emerge.
Dr.T.V.Rao MD
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24. Normal flora are Mutualistic
• Much is not known about the nature of the associations between humans and
their normal flora, but they are thought to be dynamic interactions rather than
associations of mutual indifference. Both host and bacteria are thought to
derive benefit from each other, and the associations are, for the most part,
mutualistic. The normal flora derive from their host a steady supply of
nutrients, a stable environment, and protection and transport. The host obtains
from the normal flora certain nutritional and digestive benefits, stimulation of the
development and activity of immune system, and protection against colonization
and infection by pathogenic microbes.
Dr.T.V.Rao MD
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25. Normal Flora of the Gastrointestinal Tract
Dr.T.V.Rao MD
(GIT)
• In bottle-fed infants
• Bifidobacteria are not
predominant. When breast-fed
infants are switched to a diet of
cow's milk or solid food,
bifidobacteria are progressively
joined by:
1. Enterics
2. Bacteroides
3. Enterococci
4. Lactobacilli
5. Clostridia
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26. Normal Microbial Flora of the Gastrointestinal
Dr.T.V.Rao MD
Tract
• Functions and Products of Intestinal Flora
•Intestinal microbes carry out a variety of
essential metabolic reactions that produce
various compounds
•The type and amount produced is influenced by the
composition of the intestinal flora and the diet
•Compounds produced include
• vitamins B12 and K
• gas
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27. Dr.T.V.Rao MD 27

28. The flora of the large intestine (colon)
1. Enterococci
2. Clostridia
3. lactobacilli
4. Bacteroides
5. Bifidobacterium (Bifidobacterium
bifidum)
6. Escherichia coli
7. Methanogenic bacteria
8. Viridans streptococci
9. Staphylococcus sp.
10. Proteus sp.
11. Candida albicans (Yeast)
12. Mycoplama sp.
Dr.T.V.Rao MD
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29. Normal Flora of the Respiratory Tract
A) The nares (nostrils)
1. Staphylococcus epidermidis
2. Corynebacterium
3. Staphylococcus aureus
4. Neisseria sp.
5. Haemophilus sp
6. Streptococcus pneumoniae
Dr.T.V.Rao MD
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30. Normal Flora of the Respiratory Tract
B) The upper respiratory tract
(nasopharynx).
1. Non-hemolytic streptococci
2. Alpha-hemolytic streptococci
3. Neisseria sp.
4. Streptococcus pneumoniae
5. Streptococcus pyogenes
6. Hemophilus influenzae
7. Neisseria meningitidis
Dr.T.V.Rao MD
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31. Normal Flora of the Respiratory Tract
• C) The lower respiratory tract
(trachea, bronchi, and pulmonary
tissues):
• Usually sterile.
• The individual may become
susceptible to infection by
pathogens descending from the
nasopharynx e.g.
• H. influenzae
• S. pneumoniae).
Dr.T.V.Rao MD
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32. Normal Flora of the Human Oral Cavity
• Oral bacteria include:
1. Viridans streptococci
2. Lactobacilli
3. Staphylococci (S. aureus and S.
epidermidis)
4. Corynebacterium sp.
5. Bacteroides sp.
6. Streptococcus sanguis (dental plaque)
7. Streptococcus mutans (dental plaque)
8. Actinomyces sp.
Dr.T.V.Rao MD
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33. Sites of human body that the normal flora
Dr.T.V.Rao MD
microbes colonize
• Respiratory tract and head
• outer ear, eye, mouth, oropharynx, nasopharynx
• Sterile sites: sinuses, middle ear, brain, lower
respiratory tract (trachea, bronchiole, lung)
• Gastrointestinal tract
• esophagus, stomach, small intestine, large intestine
• Genitourinary system
• anterior urethra, vagina
• Sterile sites: bladder, cervix, uterus
• Skin
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34. Normal flora may act as opportunistic
• Especially in hosts rendered
susceptible by:
• 1. Immuno-suppression
(AIDS & SCID)
• 2. Radiation therapy &
Chemotherapy
• 3. Perforated mucous
membranes
• 4. Rheumatic heart
disease…etc.
Dr.T.V.Rao MD
pathogens
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35. Normal Flora absent in …
Dr.T.V.Rao MD
Sterile tissues
In a healthy human, the internal
tissues such as:
• blood
• brain
• muscle
• cerbrospinal fluid (csf.)
are normally free of
microorganisms.
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36. Importance of The Normal Flora
Dr.T.V.Rao MD
(Advantages)
1. They constitute a
protective host
defense
mechanism
by occupying
ecological niches.
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37. Dr.T.V.Rao MD
Normal Flora of the Skin
• The most important
sites are:
1.Axilla
2.Groin
3.Areas between the
toes
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38. Importance of The Normal Flora (Advantages)
The oral flora
contribute to
immunity by inducing
low levels of
circulating and
secretory antibodies
that may cross react
with pathogens.
Dr.T.V.Rao MD
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39. Importance of The Normal Flora
1. They can cause disease
in the following:
a) When individuals
become
immunocompromised or
debilitated.
b) When they change
their usual anatomic
location.
Dr.T.V.Rao MD
(Disadvantages)
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