Microbiology
Review
Introduction to Microbiology
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Microbiology: The study of microscopic life (>1mm)
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Microbes (Micro-organisms): simple life form,
usually single celled, that can not be seen with the
naked eye.
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The term microbiology includes the study of all
microbes, including bacteria, fungi, algae, parasites,
helminths & viruses
Cell Types/Structures
Important figure in Microbiology
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Louis Pasteur (1822 – 1895) -Developed the germ
theory of disease in 1798, Pasteurization technique
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Anton van Leeuwenhoek – “father of microbiology”
– first microbiologst – invented first microscope
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Lynn Margulis – introduced and substantiated the
theory of endosymbiotic evolution
Favorable environment for bacterial/microbial
growth
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Microbes need certain conditions to survive. These include:
 Food, moisture, favorable temperature, proper gaseous
atmosphere, appropriate pH and salt concentration
If these conditions are not favorable some bacteria
will form spores to wait the return of favorable
growth conditions.
 Unlike other living beings some bacteria can live &
grow without the presence of atmospheric O2
The conditions which can inhibit or limit
bacterial growth
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Lack of food
Dryness—kills most bacteria but not spores
Medium too high or too low in pH
Antiseptics retard bacterial growth
Disinfectants kill bacteria.
Unfavorable temperature
Cold/below freezing retards growth.
Heat (boiling) kills most non-spore forming bacteria.
Light direct rays of sun & UV light are harmful to bacteria.
Growth Requirements of Bacteria:
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Bacteriologists grow bacteria by using nutrient agar, nutrient
broth, gelatin, litmus milk & other media.
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2. Food or energy sources
a. Autotrophic —inorganic, nonpathogenic
b. Heterotrophic —organic, pathogenic
Parasites — utilize living organic matter
Saprophytes — dead organic matter
3. Oxygen
a. aerobic
b. anaerobic
c. micro-aerophilic
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Growth & Reproduction
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Under favorable conditions, bacteria reproduce
by Binary fission —the cell divides in two
halves after developing a transverse furrow in
the cell wall around the bacteria.
 In a period of 12 hours, one single bacteria
may reproduce 16 million descendants to form
bacterial colonies.
Bacterial reproduction
Exponential growth
Growth curve – figure 7.18 (page 210)
 As bacteria grow, they give off poisonous
wastes & enzymes –Toxins - which may cause
disease or food spoilage
 Overpopulation & accumulation of waste kill
most bacteria
 Irregular/complex habitats and biofilms give
community stability and increase diversity
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Study of special characteristics of the cell wall
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Different stains give different colors to various
types of cell walls.
Gram negative:
cell wall is not as thick as in gram positive
bacteria
it allows to secrete toxins
Gram positive:
cell wall is much thicker compared to the gram
negative bacteria
it provides rigidity & strength to the organism
Spores
Toxins
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Endotoxins - remain within the cell
 produced by gram negative bacteria
 Signs/symptoms of endotoxins are produced
when the toxins enter the blood stream
 Exotoxins - toxins diffuse out of the cell wall
 produced by gram positive bacteria
 most potent toxins
 Responsible for tetanus, diphtheria, gas
gangrene
Relationship between living organisms
Independence
 Symbiosis
 Mutualism
 Commensalism
 Parasitism
 Antibiosis
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Classification of bacteria on the basis of cell
shape
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i) Cocci =Spherical
ii) Bacilli =Rod shaped
iii) Spirilla=Spiral shaped , or curved
Bacterial cells are often arranged into particular
patterns, because their cell walls remain attached to
each other after cell division.
Locomotion
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Many bacteria have flagella
Flagella propel the bacteria.
Most spiral shaped bacteria are motile
Sphere shaped cocci—non motile
Many rod-shaped bacteria are motile, e.g. Typhoid
bacillus— has many flagella
Endospores
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Bacilli have ability to form spores. When spores develop
nothing can enter or leave the cell. This makes the bacteria
very resistant to drying, temperature changes, & the action of
stains & disinfectants. They become hard to kill—health
hazard.
During spore stage bacterial cell is alive but inactive.
Only bacilli (rod shaped) bacteria form spores.
Spores present special problem in sterilization techniques.
Killing of spores requires strict & longer sterilization
procedures
For example, Bacillus anthracis, Clostridium species.
Bacteria
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May be harmful or beneficial.
 Pathogenic—invade animal or plant tissue to
produce diseases.
 Non-pathogenic—perform useful functions
 decomposing refuse—improve fertility of soil
 curring of tobacco, tea & coffee
 making of yogurt, cheeses- acidophilus milk
Fungi
are very simple, eukaryotic, “plantlike” structures
 do not contain chlorophyll—can not carry
photosynthesis & produce their own food.
 They are saprophytes that obtain their nutrition from
dead and decaying organic material.
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Fungi are the scavengers of the microbes.
Fungi
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Yeasts-are the unicellular forms of fungi
Molds are the multicellular, filamentous fungi—often found
on bread, cheese, and fruits
Molds are of great importance- major source of antibiotics
Both molds & yeasts have some harmful & some beneficial
members.
Yeasts are spherical or oval cells—microscopic
Molds’ filaments are visible to naked eye.
Rhizophus—black bread mold
Penicillium—used to make penicillin
Helminths (Parasitic Worms)
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Multicellular, usually macroscopic
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Produce infestation in both humans and animals
(fecal)
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Can be prevented by cleanliness
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Treated with antihelminthic drugs
Scolex (head) of a tape worm-Taenia
saginata
Protozoa
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microscopic, single celled animals - eukaryotes
larger than fungi
more complex & detailed internal structure
many protozoa have cell organelles
Responsible for diseases such as malaria, Chagas,
African sleeping sickness, Giardia
Giardia lamblia
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is a parasite found in human intestine that causes
dysentery.
 most common intestinal parasite in USA
 causes traveler’s diarrhea.
 Due to cross contamination of drinking water &
sewage
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Diagnosed by cysts or trophozoite forms.
Viruses
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smallest infections agents
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intracellular parasites-can reproduce only in host cells
 can not carry on independent metabolism
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viruses are not cellular – not autopoietic
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consist only of a nucleic acid either DNA or RNA,
surrounded by a protein coat.
Viruses continued
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the protein coat of the virus determines what type of
cells the virus can parasitize & acts to protect the
nucleic acid inside
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a virus that attacks the bacterial cells is known as a
phage or bacteriophage.
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a phage consists of a head made from a protein
membrane with 20 facets (sides) surrounding either
DNA or RNA
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the tail combines a collar attached to a tail sheath.
HIV
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HIV is carried in blood, semen, & body fluids.
usually fatal
known to be dormant for years
certain drug combinations slow the rate of
invasion of the White Blood cells by the virus.
cure is not yet on the horizon
leading cause of death in young adults, aged 2544
Prions
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Known as proteinaceous infectious particles
non-immunogenic - they do not result in the
formation of antibodies – no evolved immune
response
 Prions contain nothing but proteins. No RNA or DNA
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The known Prion diseases are all fatal and are
referred to as spongiform encephalopathies—because
they cause the brain to have holes like a sponge.
 Mad cow disease is one example.
Prions
Classification of viruses
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on the basis of:
 nucleic acid they contain
 the size, shape and structure of the virus
 the tissue the infect
Virus facts
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generally more resistant to some disinfectants
than most bacteria.
 most are susceptible to heat, except hepatitis
virus
 not affected by antibiotics
DNA viruses
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Poxivirus group (DNA) virus – pathogenic to skin small pox,
cow pox
Herpes virus group (DNA)
Latent infection may occur and lasts the life span of the host.
Cold sores
Shingles
Chicken pox
Adenovirus group (DNA)
Conjunctivitis
Papovirus group (DNA)
Wart virus
Aids Virus (Retrovirus)
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Patients are prone to develop opportunistic
infections and diseases/disorders
Incubation period (the period between becoming
infected and the actual development of the
symptoms) from 6 months up to 10 years.
Sometimes a mild illness--flu like symptoms appears
7-14 days after infection
It is accepted that once infected with HIV, AIDS will
develop at some time in the future in all cases.
At present there is no cure.
Opportunistic infections associated with AIDS can be
treated.