Microbial Habitats

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Microbial Habitats
Normal flora microorganisms normally living on
or in the body without normally causing disease.
Your body is a home to 1 x 1014 microbial cells
(bacteria)
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Key Terms
Resident
Transient
Contaminant

• Commensalism microbe benefits, host unaffected.
• Mutualism microbe benefits, host benefits.
• Opportunism change in host circumstance.

Normal flora is a significant cause of both minor
AND serious life threatening infections.
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Acquisition of normal flora

• Sterile at birth, but from then on we are
  continually exposed to microorganisms, some of
  which become established as normal flora.
• During birth maternal
• After birth dietary sources and direct contact
• NOT static, but continually changing.
• - may reflect your environment

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Location, Location, Location

• NOT all body sites have normal flora
• Sterile sites - inaccessible
• - unsuitable
• - protected
• Most external body sites have normal flora
• Skin, mouth, URT, GIT, genitourinary tract
• Nature of body SITE has a major influence on TYPE
  of normal flora - TROPISM

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Skin Flora

• Relatively inhospitable - dry
• - low pH and temperature
• - inhibitory secretions
• Location ? - surface or subsurface
• - dry or moist body site
• Body odour - role of microbes and
  anti-perspirant
• staphylococci propionibacterium yeasts

Handwashing resident, transient, contaminant
flora
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Upper Respiratory Tract Flora

• Sterile below larynx (bronchi and lungs are
  sterile)
• Common organisms - streptococci
• - Neisseria
• - haemophilus

• SPECIAL CONSIDERATION
• Streptococcus pyogenes
• Streptococcus pneumoniae
• Neisseria meningitidis
• Haemophilus influenzae

All are potentially serious pathogens at this and
other body sites.
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Gastronitestinal flora 1

• Various parts of organ system pH, O2 tension,
  nutrients
• MOUTH - paradoxically is quite anaerobic
• - 100 billion per gram tissue
• (clenched fist injuries)
• - plaque and tooth decay
• STOMACH - ? Sterile site (microbes in transit)
• - What about Helicobacter?

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Gastrointestinal flora 2

• Small versus large bowel
• 1011-12 bacteria per gram of bowel contents.
• - most are anaerobic bacteria (10001)
• - E. coli is a well known aerobic component.
• The bowel is an important source of organisms for
  infection.

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Genitourinary tract flora

• Urinary tract - sterile site ? (transient /
  protected)
• - distal urethra
• Vaginal flora
• Pre-pubescent - pH 7
• - skin and bowel flora
• Post-pubescent - pH 5
• - hormone / epithelial changes
• - lactobacilli
• Age is a strong predictor for nature of infection

LOSS of normal vaginal flora CAUSE and EFFECT
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Summary

• Normal flora is not present at all body sites.
• The types of normal flora vary with the nature of
  the body site.
• Normal flora is continually changing to reflect
  your environment and biological state.
• Normal flora is primarily bacterial with
  occasional yeasts (fungi), but no viruses, moulds
  (fungi) or parasites.
• Important to distinguish between resident,
  transient and contaminating flora.