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Types of Microbes
Prions
Prions (proteinaceous infectious particles) are infectious
proteins that are responsible for a classof diseases known as the
Transmissible Spongiform Encephalopathy (TSEs), which
areneurodegenerative diseases including Mad Cow Disease and kuru.
Prions destroy the tissue of thenervous system, forming holes in
the brain and nervous systems. Prion diseases all
involvemodification of the prion protein, a normal part of
mammalian cells. They are also all fatal andrapidly progressive.
Like viruses, prions cannot replicate on their own and rely on
other organisms.Unlike other microbes, prions do not contain
nucleic acids. Prions are thought to have originatedfrom ZIP
proteins.
Viruses
Viruses are microorganisms much smaller than bacteria that
invade other cells in order toreplicate. Viruses are responsible
for a variety of diseases, such as chicken pox. The origin
ofviruses is unclear; some may have come from plasmids (pieces of
DNA that can travel betweencells) or transposons (pieces of DNA
that can move themselves to different places in a cell'sgenome)
while others may have evolved from bacteria.
Some viruses, known as bacteriophages, infect bacteria. Their
appearance is often compared tothat of an alien landing pod.
Typically, their genome is composed of DNA rather than the RNA
ofretroviruses. Other viruses, most famously Sputnik, infect other
viruses. These are known asvirophages.
Viruses can cause either lytic or lysogenic infections. In a
lytic infection, the virus injects itsgenome into the host cell,
which cannot differentiate between viral DNA and its own DNA.
Thecell begins to make mRNA from the viral DNA, which is then made
into viral proteins that destroy
the cell's DNA. When the cell eventually shuts down, the virus
continues to use the cell toreplicate. Enough viruses are made to
cause the cell to burst, or lyse. Hundreds or thousands ofreleased
viruses then go on to infect other cells.
In a lysogenic infection, a virus integrates its DNA into the
host cell's DNA. This viral DNA is knownas a prophage. The prophage
remains dormant in the cell's DNA for several generations
beforebecoming active, leaving the cell's DNA, and directing the
synthesis of new viral proteins. HPV,which causes AIDS, is a
lysogenic virus.
Cellular MicrobesCellular microbes are microbes that are made up
of cells. There are two main types of cellularmicrobes;prokaryotes
and eukaryotes. Prokaryotes differ from eukaryotes with their lack
of
nuclei and membrane bound organelles.
BacteriaBacteria are single-celled, prokaryotic microorganisms.
Some bacteria are beneficial to humanswhile others are pathogenic,
but a majority of bacteria are harmless to humans.
Pathogenicbacteria are responsible for a variety of diseases
including strep throat and tetanus. Bacteriacome in 3 shapes:
coccus (circular), bacillus(rod-shaped), and spirillum (spirally).
Bacteriaoriginate from the single-celled organisms that were the
first to inhabit the Earth.
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Bacteria may be photoautotrophic, utilizing photosynthesis to
produce food and oxygen. Theymay also be chemoautotrophic, making
food using the energy from chemical reactions - thesebacteria serve
an important role in the nitrogen and sulfur cycles.Motile bacteria
may utilize rotating flagella to move, or they may secrete slime to
slide aroundlike a slug. Bacteria may also be nonmotile.
ArchaeaArchaea are a group of single-celled microorganisms that
were previously thought to be bacteria.Archaea are prokaryotes.
Their origin and potential for causing disease are currently
unclear;however, Archaea are thought to be ancestors of eukaryotes
or very close descendants because oftheir many similarities,
including genes and inclusion of enzymes in translation and
transcriptionprocesses. Unlike bacteria, no known species of
Archaea form spores.
Spore: Typically one-celled, reproductive unit capable of giving
rise to a new individualwithout sexual fusion. & A haploid
reproductive cell that gives rise to a gametophyte.
Archaea are capable of living in extreme habitats and anaerobic
environments. They areextremely tolerant to heat, acid, and toxic
gases. Archaea are variously involved in the carbon
and nitrogen cycles, assist in digestion, and can be used in
sewage treatment.
FungiFungi are eukaryotic organisms that can be single-celled or
multi-celled. Fungi have cell wallscomposed of chitin, unlike the
cellulose walls of plants. Fungi are heterotrophic and do not
havechloroplasts like photoautotrophs. They grow best in slightly
acidic environments and can grow inareas of low moisture.
Technically, fungi are more closely related to animals than they
are toplants and likely shared a common ancestor with animals.
Fungi are responsible for diseases suchas athlete's foot. Bakers
yeast (a fungus) is used for bread and brewing. Some fungi are used
forantibiotics and others are important decomposers in the
ecosystem.
ProtistsProtists are eukaryotic but do not have specialized
tissues. Algal protists are similar to plants andcan go through
photosynthesis, but do not have cuticles that prevent water loss.
As a result algalprotists must live in water. Animal like protists
are called protozoa and are eukaryotic andheterotrophic. These
protists consume other protists and bacteria for food. Some have
two nuclei:the macronucleus (bigger) and the micronucleus
(smaller). Many move with cilia, flagella, orpseudopodia (in the
case of amoebae). They also have complex life cycles. For example,
they may
exist in atrophozoite: (A growing stage in the life cycle of
some sporozoan parasites, when theyare absorbing nutrients from the
host.). They can also change into a dormant form known as
acyst, which can help in reproduction.Endosymbiotic Theory
Championed by Lynn Margulis in the 1960s, the endosymbiotic
theory holds that mitochondria andchloroplasts in eukaryotic cells
originated from proteobacteria and cyanobacteria,
respectively.Evidence for this theory includes that mitochondria
and chloroplasts divide through binary fission,not mitosis like the
rest of the cell. These organelles, which are the same size as
bacteria, alsohave their own different, circular DNA and two
membranes. Chloroplasts in some algae have cellwalls of
peptidoglycan.
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Gram Staining
Gram staining is a type of differential staining, meaning it
separates bacteria into two differentgroups (Gram-positive and
Gram-negative) based on their reactions to the procedure. Because
ofwidely varying responses, Gram staining cannot be performed on
archaea.
The first step in the procedure is to heat fix the bacteria;
then, those bacteria are stained withcrystal violet, the primary
stain, for one minute. In an aqueous solution, crystal
violetdisassociates into CV and CL ions, which penetrate through
the cell wall. CV ions react withnegatively charged particles in
bacterial cells and stain them purple.
The third step is to apply iodine as a mordant, or trapping
agent, for one minute. It reacts withthe crystal violet and
prevents removal of the purple stain. After the remaining iodine is
rinsedaway, alcohol decolorizer (sometimes acetone) is added until
the primary stain is removed inGram-negative bacteria because
alcohol dissolves the outer membrane. In contrast,
Gram-positivebacteria retain the primary stain because it becomes
trapped in their thick, multi-layered walls ofpeptidoglycan.
The final step is to apply safranin (sometimes basic fuchsin) as
a counterstain. This gives theGram-negative bacteria their final
red-pink color.
Characteristics ofGram-Positive BacteriaTypically, Gram-positive
bacteria produce exotoxins and are susceptible to phenol
disinfectants.They retain the blue-purple color of crystal violet
in Gram staining because of their thicker wallsof peptidoglycan.
Unlike Gram-negative bacteria, they lack the periplasmic space
between thecytoplasm and outer membranes because Gram-positive
bacteria lack an outer membrane. Certaintypes of Gram-positive
bacilli, most importantly Lactobacilli (used in milk and dairy
products),cannot form spores.
Characteristics ofGram-Negative BacteriaGram-negative bacteria
have thinner walls of peptidoglycan and two membranes and
periplasmicspace between them. Because of the safranin
counterstain, they become red-pink after Gramstaining. There are
many Gram-negative aerobic (oxygen-using) bacteria.
Viral Diseases
Viral diseases are immune to antibiotics; therefore, vaccines
are typically the best form ofprevention.y AIDS (caused by the HIV
virus)y Chicken Pox and Shingles (caused by the varicella zoster
virus)y Common cold (often caused by the rhinovirus but can also be
caused by corona viruses and
adenoviruses)y Dengue fever (caused by the mosquito-borne dengue
virus)y Ebola Hemorrhagic Fever (caused by the Ebola virus)y
Hepatitisy Herpes (caused by the herpes simplex virus type 1 and
type 2)y Influenza (caused by viruses of the family
Orthomyxoviridae)y Measles (caused by the morbillivirus)y Mumps
(caused by the mumps virus)y Mononucleosis, also known as mono or
glandular fever (caused by the Epstein-Barr virus)y Polio (caused
by the poliovirus)y Rabies (caused by the rabies virus)
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Bacterial Diseases
Bacterial diseases may often be treated by antibiotics.y
Anthraxy Botulismy Choleray Dental Caries (tooth decay)y Gonorrheay
Legionnaire's Diseasey Lyme Diseasey MRSAy Peptic Ulcer Diseasey
Pertussis (whooping cough)y Rocky Mountain Spotted Fevery Rubellay
Strep throaty Syphilisy Tetanusy TuberculosisFungal DiseasesThe
technical term for a fungal disease is a mycosis.y Athlete's footy
Histoplasmosisy Ringwormy ThrushProtozoan Diseasesy Malariay
Paralytic Shellfish Poisoningy Estuary Associated Syndromey
Giardiasisy Cryptosporidiosis
