normal and transient flora host parasite relationships n.
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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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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.
  • 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.