Dr.R.B.Y(MBBS<Running>)

Normal human flora

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Dr.T.V.Rao MD

Human microbiome

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• 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

• More bacterial than human cells in the body

•provide some nutrients (vitamin K)•stimulate immune system,

immunity can be cross-reactive against certain

pathogens•Prevent colonization by potential

pathogens (antibiotic-associated colitis, Clostridium difficile)

Normal bacterial Flora

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Dr.T.V.Rao MD

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 ▶ 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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Where to find microbe?Everywhere!

Dr.T.V.Rao MD

Introduction of Normal Flora1 . 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.

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Dr.T.V.Rao MD

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.

Outcomes of exposure to a microorganism:1. Transient colonization2. Permanent colonization 3. Disease

Normal Flora and Pathogenesis

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Dr.T.V.Rao MD

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.

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Dr.T.V.Rao MD

1. Local Environment (pH, temperature, redox potential, O2, H2O, and nutrient levels…).

2. Diet

3. Age

4. Health condition (immune activity…)

5. Antibiotics,…..etc

Factors Influencing Normal Flora

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Dr.T.V.Rao MD

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.

106 pathogenic microbes

GI infection

w/ normal flora

GI infection

w/ reduced flora afterStreptomycin treatment

10 pathogenic microbes

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Dr.T.V.Rao MD

Composition of the Normal Flora

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• 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 13

Dr.T.V.Rao MD

• 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.

When we get colonized with Normal Flora

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Dr.T.V.Rao MD

• 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

A new born child's flora is dependent on mother

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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.

Density of normal flora in Humans

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Dr.T.V.Rao MD

• Resident flora •Reflects sex

of person

Normal Flora

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Dr.T.V.Rao MD

Potential colonization sites

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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

pathogens19

Dr.T.V.Rao MD

Upper respiratory tract – and Lower Respiratory tract

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Dr.T.V.Rao MD

Common Skin Bacterium May Be New 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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Dr.T.V.Rao MD

• 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

Associations Between Humans and the Normal Flora

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Dr.T.V.Rao MD

• 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.

commensal relationship.

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Dr.T.V.Rao MD

Normal flora are Mutualistic

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• 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

Normal Flora of the Gastrointestinal Tract (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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Dr.T.V.Rao MD

Normal Microbial Flora of the Gastrointestinal 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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Dr.T.V.Rao MD

The flora of the large intestine (colon)

1. Enterococci2. Clostridia 3. lactobacilli 4. Bacteroides 5. Bifidobacterium (Bifidobacterium

bifidum)6. Escherichia coli 7. Methanogenic bacteria 8. Viridans streptococci9. Staphylococcus sp.10. Proteus sp. 11. Candida albicans (Yeast)12. Mycoplama sp.

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Dr.T.V.Rao MD

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

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Dr.T.V.Rao MD

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

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Dr.T.V.Rao MD

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).

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Dr.T.V.Rao MD

Normal Flora of the Human Oral Cavity• Oral bacteria include:

1. Viridans streptococci2. 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.

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Dr.T.V.Rao MD

Sites of human body that the normal flora 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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Dr.T.V.Rao MD

• Especially in hosts rendered

susceptible by:

• 1. Immuno-suppression

(AIDS & SCID)

• 2. Radiation therapy &

Chemotherapy

• 3. Perforated mucous

membranes

• 4. Rheumatic heart

disease…etc.

Normal flora may act as opportunistic pathogens

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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.

Normal Flora absent in …

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Dr.T.V.Rao MD

1. They constitute a protective host defense mechanism

by occupying ecological niches.

Importance of The Normal Flora (Advantages)

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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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Dr.T.V.Rao MD

The oral flora contribute to immunity by inducing low levels of circulating and secretory antibodies that may cross react with pathogens.

Importance of The Normal Flora (Advantages)

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Dr.T.V.Rao MD

1. They can cause disease in the following:

a) When individuals become immunocompromised or debilitated.

b) When they change their usual anatomic location.

Importance of The Normal Flora (Disadvantages)

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