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Background Information
What is a microbe?
Microbes are single-cell organisms so tiny that we need to use a microscope to see them. They
are the oldest form of life on earth, with fossils dating back to more than 3.5 billion years.
Microbes are found everywhere and in great abundance. For example, there are more microbes
on a person’s hand than there are people on our planet! Microbes can be found in the air we
breathe, on most surfaces (like tables and doorknobs), in the foods we eat, and even inside of
us. Two examples of microbes include viruses and bacteria.
Bacteria
Bacteria are the simplest organisms that are considered to have all the characteristics of living
things. They are prokaryotes, meaning they are simple cells that do not have an organized
nucleus (DNA is not enclosed in the nucleus). Bacteria do have cell membranes like other cells
and even a protective cell wall. Unlike plant and animal cells, they have simple materials and
structures that allow them to live.
http://www.osovo.com/diagram/prokaryoticcelldiagram.htm
Courtesy of Savio DSilva, Director Enoma
They are found in three main shapes: spherical (round), rod (like a stick), and spiral (corkscrew;
coiled). Bacteria are small single cells whose sole purpose in life is to replicate.
http://science.nasa.gov/science-news/science-at-nasa/1999/ast28may99_1/
A common misconception is that all bacteria are harmful and cause disease. The truth, however,
is that almost 99% of all bacteria are helpful, and that our existence on this planet would not be
possible without them.
Below are some examples of how bacteria are helpful:
In humans, bacteria known as Escherichia coli (E. coli) occur everywhere in the digestive
system, and aids in the breakdown of many kinds of foods as well as controls the growth
of bad bacteria. These bacteria are also responsible for the production of vitamin K and
certain B vitamins
Certain kinds of bacteria, called decomposers, are essential in the decay and
decomposition of waste materials. Decomposers break down dead materials and recycle
them back into the soil as simpler molecules that can be used as nutrients by plants
Bacteria are involved in the production of many kinds of foods we eat. For example,
bacteria such as Lactobacillus acidophilus are used in the production of yogurt. Other
kinds of bacteria are important in the production of cottage cheese, buttermilk, and
vinegar
Bacteria produce a significant portion of the oxygen we breathe
Bacteria are used to create medicines and vaccines that keep us healthy
Certain bacteria are harmful and are known as pathogens (disease causing organisms). For
example, bacteria can cause tetanus, strep throat, typhoid fever, pneumonia, syphilis, cholera,
food-borne illness, and tuberculosis. Pathogenic bacteria have certain characteristics that they
need, and use, to cause disease. These characteristics are called virulence factors and have
specific functions in causing an infection. Virulence factors include bacterial toxins, cell surface
proteins that help bacteria attach to their host’s cells, cell surface carbohydrates and proteins
that protect bacteria, and special enzymes that may contribute to the pathogenicity of the
bacterium.
An infection can be viewed as a microscopic battle between bacteria and host, the first trying to
remain present, and to feed and multiply, while the host is trying to prevent this. The resulting
infection is a process with three possible outcomes:
the host wins and the bacteria are removed (possibly with the help of medication) so
that the host can recover;
the bacteria win the ultimate battle and kill their host (bacterial infections are a major
cause of death especially for children and elderly people);
an equilibrium is reached in which host and bacteria live involuntarily together and
damage is minimized.
In order to kill harmful bacteria, antibiotics are used. The word, antibiotic, comes from the
Greek anti meaning 'against' and bios meaning 'life' (remember, a bacterium is a life form). An
antibiotic is a substance that kills or slows the growth of bacteria. This is a great tool for
eliminating unwanted bacteria and has revolutionized the modern medical arena. Antibiotics
have saved countless numbers of lives.
The challenge, however, is that many antibiotics are labeled broad spectrum antibiotics, which
are antibiotics designed to target and kill a wide range of bacteria…both bad and good. They
are not selective enough to target only harmful bacteria, and therefore end up killing the good
bacteria in our body as well. This can result in unwanted side effects leading to imbalances of
the internal ecology of the body.
While broad spectrum antibiotics have many beneficial effects, they are often used incorrectly,
and this use and abuse has resulted in the evolution of antibiotic resistant bacteria. Common
forms of antibiotic misuse include:
taking an antibiotic inappropriately, in particular when antibiotics are used to treat viral
infections, like the common cold (see information on viruses below)
failure to take the entire prescribed course of the antibiotic, usually because the patient
feels better before the infecting organism is completely eradicated
In addition to failing to effectively treat the illness for which the antibiotic was prescribed,
these practices have resulted in antibiotic resistance, as the bacteria remaining in the body
(after treatment) are hardier, and therefore produce tougher, more resilient offspring. One
extreme and dangerous example of this is a bacteria called methicillin resistant Staphylococcus
aureus (MRSA – pronounced “mersa”). This bacteria is resistant to a wide range of antibiotics
and, once acquired, can be very serious.
Methicillin resistant Staphylococcus aureus (MRSA)
http://torontoemerg.wordpress.com/2010/01/19/a-fix-for-mrsa/
The symptoms of MRSA depend on where you're infected. Most often, it causes mild infections
on the skin, causing sores or boils. But it can also cause more serious skin infections or infect
surgical wounds, the bloodstream, the lungs, or the urinary tract.
Though most MRSA infections aren't serious, some can be life-threatening. Many public health
experts are alarmed by the spread of tough strains of MRSA. Because it's hard to treat, MRSA is
sometimes called a "super bug." Some doctors and researchers are trying to use an unlikely ally
against stubborn bacteria…viruses.
Virus
Viruses are strange things that straddle the fence between being living and non-living. A virus is
not strictly alive…nor is it strictly inanimate. For example, if a virus is floating around in the air
or sitting on a countertop, they're inert. They're about as alive as a rock. However, if they come
into contact with a suitable plant, animal or bacterial cell, they jump into action. They infect
and take over the cell like pirates hijacking a ship, and their only mission to reproduce.
Whatever a virus lives in is called its host.
Unlike bacteria, most viruses do cause disease. Antibiotics do not work on viruses because
viruses are not alive. Bacteria are living, reproducing life-forms whereas viruses are just pieces
of protein and DNA (or RNA). Additionally, bacteria and viruses are structurally different, which
means that medicines used to kill bacteria will not be successful for viruses.
A virus has some fundamental information (genes made of DNA or RNA) which allows it to
make copies of itself. However, the virus must be inside a living cell of some kind before the
information can be used. Viruses need to be inside living cells to grow and reproduce. Most
viruses can't survive very long if they're not inside a living thing like a plant, animal, or person.
A virus enters a cell by first attaching to a specific structure on the cell's surface (similar to a
lock) via a specific structure on the virus surface (similar to a key). Depending on the virus,
either: a.) the entire virus enters the cell, or b.) only the genetic material of the virus is injected
into the cell (see: http://www.news-medical.net/health/What-is-a-Virus.aspx).
In either case however, the ultimate result of viral infection is the exposure of virus genetic
material inside the entered cell. Once inside the cell, the virus material essentially "takes over"
the cell and nothing but viral parts are made, which then assemble into many new complete
viruses. These viruses are mature and leave the cell either by a process called budding (just one
or a few viruses at a time leave the cell) or by a process called lysis (the cellular membrane
ruptures and releases all of the virus particles at once).
http://people.ku.edu/~jbrown/virus.html
With a virus there is nothing to "kill," so antibiotics don't work on it. Viruses cause chickenpox,
measles, flu, and many other diseases, and are quite specific about the types of cells they attack.
For example, certain viruses are programmed to attack cells in the liver, respiratory system, or
blood. In some cases, viruses called bacteriophages target and kill bacteria (phage = eat). In this
last case, the killing power of a virus (bacteriophage) can be put to good use, in a form of
treatment called antibacterial phage therapy.
Bacteriophage
Courtesy of UC Museum of Paleontology
http://www.ucmp.berkeley.edu
http://www.ucmp.berkeley.edu/alllife/virus.html
Antibacterial Phage Therapy
Phage therapy is the therapeutic use of bacteriophages to treat pathogenic bacterial infections.
As mentioned above, viruses are very specific about the kind of cells they attack, thus
bacteriophages are a class of viruses that attack bacteria cells and not human cells. This makes
phage therapy a very attractive means of destroying unwanted bacteria, such as MRSA, as it
may be more efficient and have fewer side effects to the human body than broad spectrum
antibiotics (phage therapy will not harm the good bacteria in our body).
The reproductive cycle is as follows:
1. The virus (bacteriophage) uses its tail fibers to attach itself to its target.
2. The bacteriophage gets their genetic material, which is located in the head, inside the
bacterium (The details of how this occurs varies according to the different phage types,
but their aim is always the same. For example, T4, a well-studied phage infecting the
Escherichia coli (E. coli) bacterium, contracts its tail sheath which pushes a tube located
within the tail through the membrane of the bacterial cell).
3. The phage’s DNA is passed through the tube into the cell. The phage DNA takes control,
and stops many of the cell’s vital functions, and forces it to churn out new virus
components – heads, tails, and tail fibers – in assembly-line style.
4. New viruses (bacteriophages) are fully assembled. Enzymes dissolve the wall of the
bacterium from the inside, and the newborn bacteriophages reach the exterior, ready to
attack new targets (bacteria cells). The viruses proceed very selectively as they do so.
Most of them attack only a subgroup of a single bacterial species. Generally, they don’t
touch animal or human cells, which is why they are harmless to human beings.
Just imagine this phage multiplication going on inside the mass of bacteria that fill a boil on
human skin and you get the basic idea: The phages will attack the harmful bacteria and multiply
as long as there are any bacteria left. The bacteriophage produces itself in the body until its
food (bacteria causing the infection) is gone. This is the antibacterial phage therapy.
T4 phages on the surface of a pathogenic Escherichia coli bacterium © Prof M. V. Parthasarathy,
Cornell Integrated Microscopy Center, Cornell University.
http://www.thenakedscientists.com/HTML/articles/article/virusesvssuperbugs/
Links
http://www.cds.hawaii.edu/kahana/downloads/curriculum/SectionII/Unit9/Unit9Appendix/9.X
.iii.Microbes/9.X.a.MicrobeTypes.pdf
http://www.biology4kids.com/files/micro_bacteria.html
http://kidshealth.org/kid/talk/qa/germs.html
http://www.news-medical.net/health/What-is-a-Virus.aspx
http://www.scienceclarified.com/As-Bi/Bacteria.html
http://www.wisdia.com/articles/advantages_disandvantages_of_medicines_antibiotics.aspx
http://people.ku.edu/~jbrown/virus.html
http://www.webmd.com/a-to-z-guides/bacterial-and-viral-infections
http://www.webmd.com/skin-problems-and-treatments/understanding-mrsa-methicillinresistant-staphylococcus-aureus
http://www.mrsanotes.com/phage-therapy-explained/
http://www.bacteriophagetherapy.info/ECF40946-8E2F-4890-9CA6D390A26E39C1/What%20is%20it%20all%20about.html
http://www.bacteriamuseum.org/cms/Pathogenic-Bacteria/bacterial-pathogenicity.html
http://www.mgc.ac.cn/VFs/main.htm