normal microbiota of the body

7/29/2019 Normal Microbiota of the Body

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Normal Microbiota of the Body

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Introduction Survival of host (human), depends on elaborate network

of defenses that keep harmful microorgs. and foreignmaterial from infecting the body.

If gain access, additional host defenses are summonedto prevent parasitism.

Pathogenicity: is ability to produce pathologic changesor disease.

Pathogen: is any disease producing microorganism. Nonspecific host defenses involve general, physical,

chemical and biological barriers such as inflammationand fever.

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Normal Microbiota of Body Healthy internal tissues (brain, blood, cerebrospinal fluid,

muscles) are normally free of microorgs.

Surface tissues (skin and mucous membranes) are in

contact with microorgs. and are readily colonized.

Normal microbiota: mixture of microorgs. regularlyfound at anatomical sites (mostly bacteria, less fungi and

protozoa).

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Reasons to understand normal human microbiota:

1. Specific location of microorg. provides insight into

possible infections that may result.

2. Gives investigator a perspective of the source and

significance of microorg. isolated from infection site.

3. Investigator can understand causes and

consequences of growth by microorg. normally

absent at the specific body site.

4. Awareness of role these normal microbiota play in

stimulating the host immune response can be

gained, since the immune system provides protectionagainst potential pathtogens.

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Distribution of Normal Microbiota Most important symbiotic relationships:

Commensalism: the symbiont benefits and the hostremains unharmed.

Mutualism: both symbiont and host benefit.

Parasitism: the symbiont benefits and the host isharmed.

In each category the association may be: Ectosymbiosis: one organism remains outside the other.

Endosymbiosis: one organism is present within the other.

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Skin Epidermis is not a favorable environment for microbial

colonization.

Since the skin is subjected to drying and lack of moisture

causes resident microbiota into a dormant state. But, certain parts (scalp, ears, anal regions, palms),

moisture is high to support resident microbiota.

Skin is slightly acidic due to skin oil and sweat glands,

which discourages microbial colonization. Sweat contains sodium chloride, so skin surface is

hyperosmotic and so osmotically stresses mostmicroorgs.

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Bactericidal inhibitory substances on skin control

colonization, overgrowth and infections from microorgs. Most skin bacteria are found colonizing dead cells or

close to oil and sweat glands, as secretions from glands

provide water, amino acids, urea, electrolytes and fatty

acids, which are nutrients for Staphylococcusepidermis.

Yeasts normally occur on the scalp Pityrosporumovale.

Fungi can colonize on the skin athletes foot andringworm.

Prevalent bacteria in skin glands is Propionibacteriumacnes which causes acne.

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Nose and Nasopharynx Normal microbiota of nose and nostrils is Staphylococcus

aureasand S.epidermis.

Nasopharynx (soft palate) contain potentially pathogenic

bacteria Streptococcus pneumonia, Neiserriameningitidisand Haemophilus influenza.

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Oropharynx Division of pharynx between soft palate and upper edge

of epiglottis.

S. aureusand S.epidermiscommonly habitat region.

The most important bacteria are Streptococci (S.oralis,S.milleri, S.gordonii, S.salivarius)

The palatine and pharryngeal tonsils harbour

Micrococcus and anerobes Porphyromonas, Prevotellaand Fusobacterium.

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Respiratory Tract The upper and lower respiratory tracts (trachea, bronchi,

bronchioles, alveoli) dont have normal microbiota.

Because microorgs. are removed by:

1. Continuous mucus stream generated by ciliated epithelial

cells.

2. Phagocytic action of the alveolar macrophages.

3. Bactericidal effect exerted by lysozyme enzyme in nasal

mucus.

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Mouth Normal microbiota of oral cavity contains microorgs. able

to resist mechanical removal by adhering to gums and

teeth.

If they cannot attach they removed by mechanical

flushing of oral cavity contents to stomach where they

destroyed by hydrochloric acid.

Continuous shedding of epithelial cells also removes

microorgs.

Those microorgs. that colonize in mouth find comfortable

environment due to availability of water, nutrients,

suitable pH and temp.

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Microorgs. that invade the adult mouth are anaerobes

and obligate anaerobes Porphyromonas, Prevotellaand Fusobacterium.

Streptococcus parasanguis and S.mutans attach toenamel surfaces.

S.salivarius attaches to buccal and gingival epithelialsurfaces and colonizes in saliva.

These streptococci produce glycocalyx and other

adherence factors so they can attach to oral surfaces.

These bacteria contribute to the eventual formation ofdental plaque, gingivitis and periodontal disease.

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Eye Small number of bacterial commensals are found in the

conjunctiva of the eye.

Predominant is S.epidermisand S.aureus.

Eyelids or conjunctiva yield Escherichia, Klebsiella,Proteus, Enterbacter, Neisseriaand Bacillusspecies.

Few anaerobic organisms present.

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External Ear Normal microbiota resemble those of skin, with

coagulase negative staphylococci and Corynebacteriumpredominating.

Less frequent Bacillus, Micrococcus and Neisseriaspecies.

Gram negative rods Proteus, Escherichia,Pseudomonasoccasionally seen.

Fungi is also part of normal microbiota Aspergillus,Alternaria, Penicillium, Candidaand Saccharomyces.

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Stomach Some microorgs. are washed from mouth into stomach.

Due to acidic gastric contents most are killed.

Thus stomach contains 10 viable bacteria per mm gastric

fluid Sarcina, Streptococcus, Staphylococcus,

Lactobacillusand yeasts like Candida spp.

Microorg. can survive if passed through stomach rapidly

or if ingested with food resistant to gastric pH

Mycobacteria.

Changes in microbiota found when in gastric pH

occurs following intestinal obstruction, as alkaline

duodenal secretions reflux into stomach microbiota

reflect oropharynx and gram neg. aerobic and anaerobic

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Small Intestine Is divided into 3 areas: duodenum, jejunum, ileum.

Duodenum contains few microorgs. as its combined with

stomach acid juices and inhibitory action of bile and

pancreatic secretions microbiota present are grampositive cocci and rods.

Jenjunum occassionally contains Enterococcus faecalis,lactobacilli, diphtheroids and Candoda albicansyeast.

Ileum has colon microbiota characteristics as the pH ismore alkaline anaerobic gram negative bacteria and

members of the Enterobacteriaceae family areestablished.

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Large Intestine (Colon) Has largest microbial community in the body.

Microbiota consist primarily of anaerobic, gram negative,nonsporing bacteria and gram positive, sporeforming and

nonspore forming rods. Yeast Candida albicansand protozoa occur as harmless

commensals.

Microbiota are eliminated in fecal matter as peristalsisand shedding of epithelial cells to which microorgs. areattached and continuous flow of mucus carry them out.

To maintain homeostasis of microbiota, the body mustcontinuously replace those lost microorgs.

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Under normal conditions the resident microbial

community is self regulating competition andmutualism between microorgs. themselves and their host

maintain the status.

But if the intestinal enviro. is disturbed, normal microbiota

can change greatly disruptive factors such as stress,altitude changes, starvation, parasites, diarrhea,

antibiotic or probiotic use and diet.

The typical colon of an adult is colonized by gram

negative bacteria.

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Genitourinary Tract The upper genitourinary tract (kidneys, urethras, bladder)

is usually free of microorgs.

In the distal portion of urethra few bacteria present

Staphylococcus epidermis, Enterococcus faecalis andCorynebacterium spp, sometimes Neisseria andmembers ofEnterobacteriaceaefound.

In adult females genital tract due to large surface, mucus

secretions and changes in menstrual cycle, microbiotafound are acid-tolerant lactobacilli and ferment glycogen

forming lactic acid to maintain cervical pH.

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normal microbiota of the body

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