Presentation2 Normal Flora

7/28/2019 Presentation2 Normal Flora

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Normal Flora of the Body

Dr. A. A. Wegdan


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Important Definitions Conventional Pathogens: Responsible for causing

disease in healthy individuals and account for only asmall percent of total microbial population.

Conditional Pathogens: Responsible for causing disease only in persons with reduced immunity, or whenimplanted directly into tissues, or in a normally sterilebody area.

Opportunistic Pathogens: Responsible for causinggeneralized disease but only in patients with profoundlydiminished resistance to infection.


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Important Definitions Virulence of an Organism: Is a measure of the

ability of an organism to cause disease andtransmit it from one person to another.

Infectious or Contagious Diseases: Thesediseases are caused by pathogens which havethe ability to be transmitted very easily fromperson to person.

Infection: The organisms had entered a site,had colonized and caused pathological andimmunological reactions with or without clinicalsigns.


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Important Definitions

Colonization: It is the presence of a potential pathogen that can cause infection at any time. Infact, those who progress from colonization to

infection represent only the "tip of the iceberg" of persons carrying a particular pathogen.

Carrier: Is a healthy person with a pathogen, not showing signs and symptoms of disease, but isa source of infection to others. May be atemporary state or may continue indefinitely.


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Important Definitions

Normal flora: These are a wide variety of microorganisms densely populating some surfacesand areas of the body (skin and mucous

membranes) of healthy normal persons. Commensals: Not harmful, prevent harmful

organisms from causing infection, and may beresponsible for many hospital acquiredinfections.


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Normal Flora Of The Body The skin and mucous membranes always harbor a

variety of microorganisms that can be arrangedinto two groups:

Resident flora: It consists of a fixed types of microorganisms regularly found in a given area ata given age. If disturbed, it promptly re-establishesitself.

Transient flora: It consists of nonpathogenic or

potentially pathogenic microorganisms that inhabitthe skin or mucous membranes for hours, days or weeks. They are easily removed mechanically bywashing, by natural body fluids or by use of disinfectants.


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Role of Normal flora Resident flora of certain

areas plays a definite role inmaintaining health andnormal function, e.g.

resident flora of theintestine synthesize vitaminK, niacin, thiamin and aid inthe absorption of nutrients.

On mucous membranesand skin, the resident floramay prevent colonization bypathogens through bacterialinterference.


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Role of Normal flora Members of the normal

flora may themselvesproduce disease under certain conditions:

1. If introduced into the bloodstream, e.g. viridans streptococci .

2. If they change their natural

site, e.g. E. coil, in urinarytract infection.

3. In immuno-compromisedindividuals.


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Normal Flora of the Skin Staph. aureus colonizes the nose and

perineum. Staph. epidermidis and micrococci.

Aerobic and anaerobic diphtheroids . Non-pathogenic Neisseria species. Alpha hemolytic and non-hemolytic

streptococci . Saprophytic mycobacteria , e.g. M. smegmatis . Small numbers of other organisms, e.g.

Candida species in skin folds.


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Normal Flora of the Gastrointestinal Tract

At birth, the intestine is sterile butorganisms are soon introduced with food.

In the normal adult, stomach and upper part of small intestine are sterile due tostomach acidity and intestinal enzymes.

Large number of flora are found in theterminal ileum.


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Normal Flora of the Vagina

Soon after birth , pH of the vagina is acidicunder influence of maternal estrogen (severalweeks), so lactobacilli appear in the vagina.

Before puberty , pH becomes neutral or alkaline, and there are mixed flora e.g. S.epidermidis , anaerobic streptococci .

At puberty and till menopause , lactobacillireappear and contribute to the maintenance of acidic pH .


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Presentation2 Normal Flora