Chapter 10. Microbial Ecology
and Microbial Biotechnology
• Chapter 10 Outline
• Symbiotic Relationships Involving Microorganisms
• Indigenous Microflora of Humans
• Beneficial and Harmful Roles of Indigenous
Microflora
• Microbial Communities (Biofilms)
• Agricultural Microbiology
• Microbial Biotechnology
• 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.
• 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
• 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)
• Indigenous Microflora of Humans, cont.
• Microflora of the Respiratory Tract, cont.
– Upper respiratory tract (nasal passages
and throat) has an abundance of
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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
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
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 500-600 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.
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
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
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
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
bacteria secrete; the bacteria grow in tiny clusters
called microcolonies, separated by water channels
• Biofilms have medical significance; they form on
urinary catheters and medical equipment and can
cause diseases like endocarditis
Microbial Communities, cont.
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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.
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)
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).
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.
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”
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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).