Transcript Significance of The Normal Flora

Human Microbial Flora
Dr. Waleed Khlaid
Lec. : 4
Human microbial flora
-They are a mixture of microorganisms regularly
found at any anatomical site on /within the body
of a healthy person.
-Normal
flora include bacteria and fungi .
-Some of these microorganisms are found in
association with humans / animals only. Others are
found in the environment as well.
It is estimated that 500 to 1000 species of
bacteria live in the human body .

Composition of normal flora depends upon
many various factors including genetics, age,
sex, stress, nutrition , antibiotics and diet

Although normal flora are found on all
surfaces exposed to the environment (on the
skin and eyes, in the mouth and nose), the vast
majority of bacteria live in the large intestine.

Symbiotic relationship:
-Symbiotic relationship means that normal
flora derives a supply of nutrients, a stable
environment, constant temperature, protection
and transport from the host . On the other
hand, the host obtains from the normal flora
certain nutritional benefits, stimulation of the
immune system, and colonization strategies
that inhibit potential pathogens from
occupying certain site.
Symbiotic relationship
Normal Microbial Flora Groups
Resident flora
Consists of relatively fixed types of
microorganisms regularly found in a given area
at a given age.
Transient flora
Consists of microorganisms that live in the skin
or mucous membranes for hours, or days.
Distribution of normal flora in human
body
-Normal flora are regularly
found in different anatomical
sites of human body .
-The vast majority of bacteria
live in the large intestine
-Some body parts are normally occupied by normal
flora , while other components and parts are normally
devoid from any microorganism and its presence in
these sites and components indicate that there is an
infection. These sites and tissues are termed as
sterile .
-Examples of sterile tissues are:- Blood
- Brain
- Muscle
- Cerbrospinal fluid (CSF)
Sites of human body that the normal
flora microbes colonize
1-Skin
2-Head and respiratory tract
Eye, mouth, nasopharynx and ext. ear.
Sterile sites: sinuses, middle ear,
lower respiratory tract and lung
3-Gastrointestinal tract
Esophagus, stomach, small intestine
and large intestine
4-Genitourinary system
Anterior urethra and vagina
•The explanations for why the normal bacterial
flora are located at particular anatomical sites
include:1) Tissue tropism – one explanation of tissue tropism
is that in one site the host provides an essential
growth factors needed by the bacterium, while on
the other sites the host may produce acids, bile
salts and lysozymes making these sites not
favourable for the microbial flora to live .
2) Many of the normal flora are able to specifically
colonize a particular tissue or surface using their
own surface components like capsules, fimbriae,
and cell wall components as specific tools for the
attachment to specific receptors located at the
colonization sites .
Significance of The Normal Flora
(Advantages and Disadvantages)
1.Immunostimulation
a)
They produce antibodies which may contribute
to host defenses.
b)
Some of these antibodies may cross react with
normal tissue components (autoimmunity).
2) Protection from External Invaders
-The normal flora occupy body’s epithelial surfaces,
so they are able to prevent other pathogenic bacteria
from establishing themselves by
A) Blocking receptors (attachment).
B) Competing for essential nutrients.
C) Producing anti-bacterial substances e.g. fatty
acids, peroxides and bacteriocines.
Normal Flora Competing With
Invading Pathogens
3) Nutrition
-Some of the normal intestinal flora like E. coli &
Bacteroids produce Vitamin K in the gut which is
available for use by the host.
4)Food metabolism
- They participate in food metabolism
by producing proteolytic enzymes and
some substances that digest
carbohydrates .
5) Production of Carcinogens
-Some normal flora may modify, through their
enzymes, some chemicals in our diets into carcinogens
e.g. artificial sweeteners may be enzymatically
modified into bladder carcinogens.
6) Opportunistic infections
Normal flora may become a source of opportunistic
infections , e.g. in-patients with impaired defense
mechanisms.
OPPORTUNISTIC INFECTION is an infection that
is caused by an opportunistic pathogen which is a
microorganism that is normally present as a
commensal that does not harm its host but can cause
disease when the host’s resistance is low .
opportunistic pathogens can cause disease in the
following conditions:
a) When individuals become immunocompromised
or debilitated.
b) When they change their usual anatomic
location.
1-Skin Flora
-Human adult has 2 square meters of skin , and it is
considered as a hostile environment for the normal
flora specially in the following sites :
1.
2.
3.
Axilla
Groin
Areas between the toes ( Toe webs )
-These regions often have the largest number of skin
flora because they provide the moisture that is
needed for the bacterial growth.
• Most common skin flora include :– Staphylococcus aureus,
– Staphylococcus epidermidis
– Propionibacterium acnes
2-Oral Cavity Flora
-Streptococci are the most common flora in the oral
cavity specially Viridans group Streptococci ,one
member of this group, Streptococcus mutans, is
the etiological agent of dental caries.
-If they are introduced into the bloodstream, they
have the potential of causing endocarditis, in
particular in individuals with damaged heart valves.
They are the most common causes of subacute
bacterial endocarditis.
3-Nasopharyngeal Flora
-Many potential pathogens may be found in the
nasopharynx of a healthy individual .
• Most common nasopharyngeal flora include :– Streptococcus pneumoniae
– Neisseria meningitidis
– Haemophilus influenzae
4-Intestinal Flora
-The intestinal tract is another hostile environment for
microorganisms.
-The stomach contain little amount of normal flora due to
presence of gastric acid , while the colon may contain 109 to
1011 bacteria per gram of material, and 25%-35% of fecal
mass is composed of bacteria .
-These organisms inhibit the growth of other pathogens but
some can be opportunistic (e.g. Clostridium difficile that can
produce pseudomembranous colitis) .
5-Urogenital Flora
-The urogenital tract is normally sterile with the
exception of the vagina and the distal 1 cm of
the urethra
Urethra :It may contain predominantly skin microorganisms
including staphylococci, streptococci and
diphtheroids
-Vagina
The genus Lactobacillus predominate in the vagina,
Lactobacillus generally lower the pH to around 4-5
which is optimal for the lactobacilli but inhibitory
for the growth of many other bacteria.
Loss of this protective effect by antibiotic
therapy can lead to infection by Candida ("yeast
infection")
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