microbial flora-of-the-human-body

Dr. Rashad Shawgi BabikerM.Sc. (Microbiology)

(UMST)M.Sc. Stud. (Immunology )Institute of Tropical Medicine.

(SAS)

Normal FloraDefinition

Normal flora is the mixture of microorganisms (bacteria and fungi) that are regularly found at any anatomical site of human body.

Symbiotic Relationship1. Mutualistic

Both organisms benefit – “mutually benefical”

2. CommensalisticOne organism benefits, the other is neither

helped nor harmed

3. OpportunisticUnder normal conditions, microbe does not

cause disease, but if conditions become conducive , it can cause disease

MutualisticEscherichia coli

Synthesizes Vitamin K & B complex Vitamins

In return, we provide a warm, moist nutrient rich environment for E. coli

CommensalisticWe have no Commensalistic relationships with

Bacteria

If Bacteria are in or on our body, they are either helping us (Microbial Antagonism) or harming us.

OpportunisticEscherichia coli - normally in our digestive

tract where it causes no problems, but if it gets into the urinary tract it can become pathogenic.

Staphylococcus aureus – commonly found in the upper respiratory tract, but if it gets into a wound or a burn it can become pathogenic

The Three Types of Symbiotic Relationships

Table 14.1

Normal Microbial Flora1. Resident Flora

Microbes that are always present

2. Transient FloraMicrobes that live in or on your body for a

period of time (hours, days, weeks, months) then move on or die off

Transient MicrobiotaRemain in the body for only hours to

months before disappearing

Found in the same regions as resident microbiota

Cannot persist in the body…because…Competition from other microorganismsElimination by the body’s defenses cellsChemical or physical changes in the

body

Sterile tissuesIn a healthy human, the

internal tissues such as:

blood brain muscle cerbrospinal fluid (csf.) are normally free of

microorganisms.

Normal Flora

Normal Flora Skin Eyes (i.e.Cunjunctiva) Nose (i.e. Respiratory

tract) Mouth (i.e Human

Oral Cavity) Ears Urogenetal tract Elementry tract

Normal FloraResident flora

Acquired rapidly during & after birth

Normal FloraResident flora

Reflects age of personChanges continuously

through out lifeReflects nutrition of

personReflects genetics of

personReflects environment

of personReflects sex of person

1. They constitute a protective host defense mechanism by occupying ecological niches.

Importance of The Normal Flora (Advantages)


2. They produce vitamin B and vitamin K in intestine.


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


4. The oral bacteria flora exert microbial antagonism against nonindigenous species by production of inhibitory fatty acids, peroxides, bacteriocins, etc.


5. The normal flora may antagonize other bacteria through the production of substances which inhibit or kill nonindigenous species.

Importance of The Normal Flora (Disadvantages)1. They can cause

disease in the following:a) When individuals become immunocompromised.b) When they change their usual anatomic location.

Contamination vs. Infection

Contamination – the mere presence of microbes in or on the body

Infection – results when the organism has evaded the body’s external defenses, multiplied, and become established in the body

Portals of Entry

Sites through which pathogens enter the body

Four major typesSkinMucous membranesPlacentaParenteral route

SkinOuter layer of packed, dead, skin cells

usually acts as a barrier to pathogens

Some pathogens can enter through openings or cuts

Others enter by burrowing into or digesting the outer layers of skin…flesh-eating bacteria

Mucous MembranesLine the body cavities that are open to

the environmentProvides a moist, warm environment

that is hospitable to pathogens

Respiratory tract is the most commonly used site of entry – entry is through the nose, mouth or eyes

Pathogens able to survive the acidic pH of the stomach may use the gastrointestinal tract as a route of entry

Some Pathogens that Cross the Placenta

Table 14.3

Parenteral Route

Pathogens deposited directly into tissues beneath the skin or mucous membranes

Infection vs. Disease

Infection is the invasion of the host by a pathogen

Disease results only if the invading pathogen alters the normal functions of the body

Disease is also referred to as morbidity

Manifestations of DiseaseSymptoms – subjective characteristics of

disease felt only by the patientSigns – objective manifestations of disease

that can be observed or measured by othersSyndrome – group of symptoms and signs that

characterize a disease or abnormal conditionAsymptomatic, or subclinical, infections lack

symptoms but may still have signs of infection

EtiologyStudy of the cause of disease

Germ theory of disease – disease caused by infections of pathogenic microorganisms

Robert Koch developed a set of postulates one must satisfy to prove a particular pathogen causes a particular disease

microbial flora-of-the-human-body

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