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Burton's Microbiology
for the Health Sciences
Chapter 10. Microbial Ecology
and Microbial Biotechnology
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Chapter 10 Outline
• Introduction
• Symbiotic Relationships Involving Microorganisms
• Indigenous Microflora of Humans
• Beneficial and Harmful Roles of Indigenous Microflora
• Microbial Communities (Biofilms)
• Agricultural Microbiology
• Microbial Biotechnology
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Indigenous Microflora of Humans
• Includes all the microbes
(bacteria, fungi, protozoa
and viruses) that reside on
and within a person;
sometimes referred to as
our “normal flora”
• Blood, lymph, spinal fluid,
and most internal tissues
and organs are normally
free of microorganisms (i.e.,
they are sterile).
• Transient microflora take up
temporary residence on and
within humans.
• Destruction of resident
microflora disturbs the
delicate balance between
host and microorganisms.
Normal flora of the oral cavity
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Areas of the body where
most of the indigenous
microflora reside.
Indigenous Microflora of Humans,
cont.
• Microflora of the Skin
– Primarily bacteria and
fungi – about 30
different types; most
common =
Staphylococcus spp.
– Number and variety of
microorganisms depend
on:
• Amount of moisture
present
• pH
• Temperature
• Salinity
• Presence of chemical
wastes and other
microbes
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Indigenous Microflora of Humans,
cont.
• Microflora of the Ears and Eyes
– Middle ear and inner ear are usually sterile;
outer ear and auditory canal contain the
same microorganisms as on the skin
– Eye is lubricated and cleansed by tears,
mucus and sebum – few microorganisms
present
• Microflora of the Respiratory Tract
– Divided into upper respiratory tract (nasal
passages and throat) and lower respiratory
tract (larynx, trachea, bronchi and lungs)
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Indigenous Microflora of Humans,
cont.
• Microflora of the Respiratory Tract,
cont.
–
Upper respiratory tract (nasal
passages and throat) has an
abundance of microorganisms;
many are harmless, some are
opportunistic pathogens
–
Carriers harbor virulent pathogens
in their nasal passages or throats,
but do not have the diseases
usually caused by these pathogens
• Examples: people harboring the
bacteria that cause diphtheria,
pneumonia, meningitis, and
whooping cough
–
Lower respiratory tract is usually
free of microbes
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Indigenous Microflora of Humans,
cont.
• Microflora of the Oral Cavity
(Mouth)
– A shelter for numerous
anaerobic and aerobic
bacteria; remaining food
particles provide a rich
nutrient medium for
bacteria
– Careless dental hygiene
may cause:
• Dental caries (tooth
decay)
• Gingivitis (gum
disease)
• Periodontitis
– The most common
organisms within the
indigenous microflora of
the mouth are various
species of alpha-hemolytic
streptococci
pneumonia
Peptostreptococcus
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Indigenous Microflora of Humans,
cont.
• Microflora of the
Gastrointestinal (GI) Tract
–
The colon (large intestine)
contains the largest
number and variety of
microorganisms of any
colonized area of the
body; an estimated 500600 different species primarily bacteria.
–
Colon is anaerobic;
bacteria in colon are
mostly obligate-,
aerotolerant-, and
facultative anaerobes.
–
Many of the microflora of
the colon are
opportunists.
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Indigenous Microflora of Humans,
cont.
• Microflora of the Genitourinary (GU)
Tract
–
The GU tract consists of the
kidneys, ureters, urinary bladder,
urethra, and parts of the
female/male reproductive
systems
–
Kidney, ureters and urinary
bladder are usually sterile; the
distal urethra and its external
opening harbor many microbes
including bacteria, yeasts and
viruses
–
Most frequent causes of urethral
infections include Chlamydia
trachomatis, Neisseria
gonorrhoeae, and mycoplasmas
–
The male and female reproductive
systems are usually sterile, with
the exception of the vagina
Chlamydia trachomatis
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Beneficial and Harmful Roles of
Indigenous Microflora
• Humans derive many benefits
from their indigenous microflora;
examples - vitamins K and B12.
• Microbial Antagonism
– Means “microbes versus
microbes”
– Many members of our
indigenous microflora are
beneficial in that they
prevent other microbes from
becoming established
– Other examples of microbial
antagonism involve:
• Production of antibiotics
and bacteriocins
(antibacterial proteins);
an example is colicin,
produced by E. coli
E. coli
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Beneficial and Harmful Roles of
Indigenous Microflora, cont.
• Opportunistic Pathogens and
Biotherapeutic Agents
–
Opportunistic pathogens are
those microorganisms that
“hang around,” waiting for the
opportunity to cause infection
• Examples: E. coli, other
members of the family
Enterobacteriaceae, S.
aureus, and Enterococcus
spp.
–
The delicate balance of the
indigenous microflora can be
upset by antibiotics, other
types of chemotherapy, and
changes in pH
–
Bacteria and yeasts used to
stabilize the microbial balance
are called biotherapeutic
agents or probiotics
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Microbial Communities
• It is rare to find an ecologic niche
in which only one type of
microorganism is causing a
particular effect
• Microorganisms are often
organized into biofilms – complex
communities of assorted
organisms. Biofilms are
everywhere; example – dental
plaque.
• Biofilms consist of a variety of
different species of bacteria plus a
gooey polysaccharide that the
Iodine staining of biofilm plaque
bacteria secrete; the bacteria
grow in tiny clusters called
(upper right)
microcolonies, separated by water
channels
• Biofilms have medical significance;
they form on urinary catheters
and medical equipment and can
cause diseases like endocarditis
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Microbial Communities, cont.
• Microbes commonly associated with
biofilms on medical devices include
the yeast, Candida albicans, and
bacteria like Staphylococcus
aureus, Enterococcus spp.,
Klebsiella pneumoniae, and
Pseudomonas aeruginosa.
• Biofilms are very resistant to
antibiotics and disinfectants
–
Antibiotics that are effective
against pure cultures of
organisms have been found to
be ineffective against those
same organisms within an
actual biofilm
• Bacteria in biofilms produce
different types of proteins that may
not be produced by the bacteria in
pure culture.
Biofilm on contact lenses
http://www.clspectrum.com/pr
intarticle.aspx?article=102915
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Synergistic Infections
• When 2 or more organisms
“team up” to produce a
disease that neither could
cause by itself
• The diseases are called
synergistic infections,
polymicrobial infections, or
mixed infections
– Examples:
• Acute necrotizing
ulcerative gingivitis
(ANUG, trench
mouth, or Vincent’s
disease).
• Bacterial vaginosis
(BV)
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Agricultural Microbiology
• There are many uses for
microorganisms in
agriculture
• Role of Microbes in Elemental
Cycles
– Microorganisms play an
important role in the
cycling of nutrients and
elements like nitrogen,
carbon, oxygen, sulfur,
and phosphorus.
• N2 is converted by
nitrogen-fixing
bacteria and
cyanobacteria into
ammonia (NH3) and
ammonium ion (NH4).
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Root nodules
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Agricultural Microbiology, cont.
• Other Soil
Microorganisms
– There are a
multitude of other
microorganisms in
soil – bacteria,
fungi, algae,
protozoa, viruses,
and viroids; many
are decomposers.
– A variety of
human pathogens
live in soil
including
Clostridium spp.
(such as C. tetani
and C. botulinum)
and the spores of
Bacillus anthracis.
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Biotechnology
• Defined as “any technological
application that uses biological
systems, living organisms, or
derivatives thereof, to make or
modify products or processes for
specific use”
• Microbes are used in a variety of
industries, including the production
of certain foods and beverages, food
additives, vaccines, and antibiotics.
• Microbes are used in the production
of foods like bread, cheeses, olives,
pickles, vinegar and yogurt, as well
as in the production of alcoholic
beverages like beer and wine.
• Many antibiotics and drugs are
produced in pharmaceutical
companies by fungi and bacteria
(penicillin for example).
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins