Normal and transient flora host parasite relationships
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Normal and Transient Flora; Host/Parasite Relationships. Microbial Ecology. The study of microorganisms and their environment. Symbiosis. “living together”

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Normal and transient flora host parasite relationships
Normal and Transient Flora;Host/Parasite Relationships

Microbial ecology
Microbial Ecology

  • The study of microorganisms and their environment.


  • “living together”

  • Describes the interactions that occur between two dissimilar organisms (usually 2 different species) that live together or are in close association with one another.

  • Symbionts

    • the organisms that live together in such a relationship.


  • Symbiotic relationship in which neither symbiont is affected by the relationship.

  • Both species are unaffected.


  • Symbiotic relationship in which one symbiont benefits and the other species is not affected (neither harmed nor helped).

  • Ex. Propionibacterium

    • many species in this genera live on the skin and are thought to neither hurt nor help humans.

  • Host

    • An organism that harbors another organism.

  • Mutualism

    • Symbiotic relationship that is beneficial to both symbionts.

    • Ex. Termites and protozoa

    • Ex. Lichens

    • Ex. Some species of our microflora (i.e. Escherichia coli.)



    E. coli.


    • Symbiotic relationship in which one symbiont is benefited and the other is harmed.

    • Ex. Sheep liver fluke

    • Ex. Opportunistic pathogens of our normal flora.

    Sheep Liver

    Synergistic relationship
    Synergistic Relationship

    • When two (or more) microorganisms “team up” to cause a disease that neither could cause by itself.

    • Called synergistic infections.

    • Ex. Acute necrotizing ulcerative gingivitis (i.e. “Trench Mouth).

    Acute necrotizing ulcerative gingivitis.

    Normal flora of humans
    Normal Flora of Humans

    • All microbes that reside on and within a person.

    • Most commonly inhabited parts of the body.

      • Eyes

      • Skin

      • Mouth

      • Ears

      • Upper respiratory tract

      • Gastrointestinal tract

      • Genitourinary tract

    Establishing normal flora
    Establishing Normal Flora

    Transient flora
    Transient Flora

    • Live temporarily on the body.

    • Often “picked up” from our daily routines.

    • Why are they temporary?

    Importance of normal flora
    Importance of Normal Flora

    • Often helps prevent infection.

    • Prolonged use of antibiotics can cause an imbalance.

    • Ex. Candida albicans

    Candida albicans.

    Candida albicans infection.

    Microflora of the skin
    Microflora of the Skin

    • Consists of mostly bacteria and fungi.

    • Most are anaerobes, although some are aerobic.

    • Anaerobes live in the:

      • deeper layers of the skin

      • hair follicles

      • sweat and sebaceous glands

    Microflora of the skin1
    Microflora of the Skin

    • The number and variety of microorganisms depends on the:

      • Amount of moisture present

      • pH

      • Temperature

      • Salinity

      • Presence of chemical wastes such as urea and fatty acids

      • Presence of other microbes (which may produce toxic substances)

    Groups of normal skin flora
    Groups of Normal Skin Flora

    • 1. Diphtheroids (Coryneforms)

      • Gram-positive, non-spore forming rods.

      • Ex. Propionibacterium acnes.

  • 2. Staphylococcus spp.

    • Gram-positive cocci usually arranged in clusters.

    • Helps maintain normal flora balance.

  • 3. Yeasts – Candida spp.

    • Single-celled fungi.

    • Ex. Causes tinea versicolor.

  • Propionibacterium acnes.

    Tinea versicolor.

    Microflora of the eyes and ears
    Microflora of the Eyes and Ears

    • Ears

      • Middle ear and inner ear sterile.

      • Outer ear and auditory canal contain same types of microorganisms as are found on the skin.

  • Eyes

    • Does contain some microorganisms.

    • Tears, mucus, and sebum that are produced in and around the eye greatly reduce many microorganisms.


    Respiratory tract
    Respiratory Tract

    • Upper Respiratory Tract

      • Nasal passages

      • Throat (pharynx)

  • Lower Respiratory Tract

    • Larynx (voice box)

    • Trachea

    • Bronchi

    • Bronchioles

    • Lungs


    Microflora of the respiratory tract
    Microflora of the Respiratory Tract

    • Upper Respiratory Tract

      • Nasal Passages and Throat

        • Have many species of microorganisms.

        • Provide moist, warm environment.

        • Many are harmless.

        • Some are opportunistic pathogens.

        • Some people are carriers of virulent pathogens.

  • Lower Respiratory Tract

    • Usually microbe free.

  • Microflora of the upper respiratory tract
    Microflora of the Upper Respiratory Tract

    • Staphylococcus spp.

      • Gram-positive cocci in clusters.

      • Often includes S. aureus.

  • Corynebacterium spp.

    • Gram-positive rods; nonmotile; nonspore-forming.

    • Nonpathogenic species.

    • Collectively called diphtheroids.

  • Moraxella spp.

    • Gram-negative diplococci.

    • Resemble Neisseria species.

  • S. aureus

    Corynebacterium spp.

    Moraxella spp.

    Microflora of the upper respiratory tract cont
    Microflora of the Upper Respiratory Tract cont.

    • Haemophilus spp.

      • Small, gram-negative rods.

      • Often includes H. influenzae.

  • Bacteroides spp.

    • Small, gram-negative rods.

    • Strict anaerobes.

  • Streptococcus spp.

    • Gram-positive streptococci in chains.

    • Often includes S. pneumoniae.

  • H. influenzae

    Bacteroides fragilis

    Streptococcus spp.

    Microflora of the oral cavity
    Microflora of the Oral Cavity

    • Provides great shelter and nutrients for many species of microbes.

    • Flourish in gum margins, crevices between teeth, and deep fold of the tonsils.

    • Bacteria feed on food particles and dead epithelial cells.

    • Poor hygiene can lead to periodontal diseases.

    • Most common microbes are species of alpha-hemolytic streptococci.

    Gastrointestinal tract
    Gastrointestinal Tract

    • Digestion of food, absorption of nutrients, and elimination of undigested material.

    • Includes:

      • Oral cavity and throat (already discussed)

      • Esophagus

      • Stomach

      • Small intestines

      • Large intestines

      • Anus

    Microflora of the gastrointestinal tract
    Microflora of the Gastrointestinal Tract

    • Stomach

      • Acidic environment prevents much growth.

      • Exception – Helicobacter pylori – found in some people causes ulcers.

  • Small Intestine

    • Upper part of small intestine (duodenum) – little growth due to bile.

    • Lower portion of small intestine (jejunum and ileum) – more microbial growth present.

  • Large intestine (colon)

    • Contains the largest number and variety of microbes.

    • 500-600 species.

    • Anaerobic environment.

    • Contains obligate anaerobes, aerotolerants, and facultatives.

    • Many are opportunistic pathogens if enter other areas of the body.

  • Genitourinary tract
    Genitourinary Tract

    • Urinary Tract

      • Kidneys

      • Ureters

      • Urinary bladder

      • Urethra

  • Male and Female Reproductive Systems


    Microflora of the genitourinary tract
    Microflora of the Genitourinary Tract

    • Healthy kidneys, ureters, and urinary bladder are sterile.

      • Urethra harbors many microbes (i.e. yeasts, bacteria, and viruses).

      • Usually don’t invade bladder due to acidic nature of urine.

      • UTI (urinary tract infections) occur when microbes travel up the urethra and multiply.

  • Male and female reproductive systems are sterile with the exception of the vagina.

    • Type of growth depends on stage of sexual development.

    • pH of vagina changes throughout sexual development providing different environments for different organisms.

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