Final Modeling Project
Bacteria Growth In the Human
Bloodstream
GEOS 2004
December 8, 2000
Molly Bender – Pre-Social Work
Shauna Griggs – Microbiology
Clint Guerrero – Music
Vicky La – Elementary Education
Eleanor Ware – Elementary
Education
Introduction
Our
group had originally planned to find a model dealing with the increase and
decrease of population of an animal, so we chose a deer population model. This model was rather simple but also had
some problems, so it was suggested that we change to a slightly more complex
model that still portrayed a predator-prey component. Finding a downloadable predator-prey model was actually very
difficult. We found numerous models,
but not a downloadable Stella model.
They were all figures, pictures, or diagrams that could be seen visually
on line, but could not be manipulated.
Finally we did find some models that were downloadable, but were either
extremely complex or not functioning properly.
So we continued our search for a suitable model that would be
interesting.
We finally came upon a
model that seemed appropriate that dealt with the increase and decrease of
bacteria population due to environmental factors. Steve Uyed and Mike Slootmaker from the Catalina Foothills
Schools District in Tucson, Arizona created this model. It was not exactly the predator-prey model
that we had in mind such as our original one, but it could also still be
categorized as a predator-prey model where the bacteria is the predator
attacking the prey, or human. It was
not too complex to work with but also slightly more complex than our original
model.
This model is actually very interesting because it deals
with a process that is a major concern or interest to millions. Everyone is affected by bacteria, either in
a positive or negative manner. The
model mainly focuses on the negative aspects of bacteria that could result in
diseases, or pathogens. This model was
created to be used by grades ranging from 6th to 12th
grades, but these particular activities were aimed toward 9th graders. We felt that this model dealt with real-life
situations so would be a great activity to use in any classroom. By producing a model that demonstrates the
increase and decrease of bacteria population due to different factors would be
a great hands-on learning experience.
For the first activity the lesson discusses the two
phases of investigating the history of pathogenic organisms. This is done prior to treatment of
infectious diseases. The first phase is
to find out how the organism uses resources found in its environment for
survival. The second is studying how
the environmental conditions affect the increase or decrease in pathogen
population.
This
model mostly explores the influence of temperature and pH of human blood on the
population size of a bacteria culture.
It also aims to finding what are some of the limiting factors that
affect growth of bacteria. This in turn
can help to learn more about how antibiotics work.
Our group has broken down the model into different
categories where each person would have to discuss different components of the
model. Each of the group members will
do research in finding general information that deals with their component of
the model. Then each of us will find
information about each component in reference to the model as well, including
producing graphs will the model. The
different categories are divided up as so:
Vicky La: Introduction of
Bacteria/Toxins in reference to bacteria and to
the model.
Clint Guerrero: Bacteria in general and in reference
to the model.
Eleanor Ware: Food in reference to bacteria and the
model.
Molly Bender: Temperature in reference to
bacteria and the model.
Shauna Griggs: pH in reference to bacteria and the
model.
A downloadable version of
this model is available on the Internet at http://www.clexchange.org/cle_lom_science.html
Bacteria
Bacteria are simple
organisms that consist of one cell.
They are among the smallest living things. Most bacteria measure from .3 to 2.0 microns in diameter (.0003
to .002 millimeters) and can only be seen through a microscope. Bacteria exist almost everywhere, though
most are harmless to humans. In fact,
there are many different types of bacteria that are helpful to humans.
Helpful bacteria are essential to many physical
processes. Certain kinds of bacteria
live in the intestines of human beings and animals. These bacteria help with digestion and in destroying harmful organisms. Intestinal bacteria also produce some
vitamins that are vital to the human body.
Bacteria in soil and water play a crucial role in recycling carbon,
nitrogen, sulfur and other chemical elements used by living things. Many bacteria help decompose dead organisms
and animal wastes into chemical elements.
Other bacteria help change chemical elements into forms that can be used
by plants and animals. For example,
certain kinds of bacteria convert nitrogen in the soil and air into nitrogen
compounds that can be used by plants during certain metabolic processes. The structure of bacteria is important to
such processes.
Nearly
all kinds of bacteria are enclosed by a tough protective layer called a cell
wall. The cell wall gives the bacterium
its shape and enables it to live in a wide range of environments. Some bacteria are also enclosed by a slimy
layer outside the cell wall called a capsule.
The capsule makes the cell resistant to destructive chemicals. All
bacteria have a cell membrane, an elastic, baglike structure just inside the
cell wall. Small molecules of food
enter the cell through pores in this membrane, but large molecules cannot pass
through. Inside the membrane is the
cytoplasm, a soft, jelly-like substance.
The cytoplasm contains chemicals called enzymes, which help breakdown
food and build cell parts. To see a
diagram of the structure of a bacteria cell, go here. The
structure of bacteria cells, along with other factors discussed in our model
such as pH level, temperature and food supply strongly affect how long bacteria
lives.
Bacteria live almost
everywhere, even in places where other forms of life cannot survive. The air, water, and upper layers of soil
contain many bacteria. Bacteria are
always present in the digestive and respiratory systems and on the skin of
human beings and other animals. Certain
bacteria called aerobes require oxygen to live, but others known as anaerobes
can survive without it. Some anaerobes
can exist either with or without oxygen.
Other anaerobes cannot live with even a trace of oxygen in their
environment. Bacteria can only thrive
in a specific temperature range.
Approximately, bacteria can grow and reproduce in temperatures hotter
than 4 degrees Celsius (39.2 degrees Fahrenheit), and colder than 60 degrees
Celsius (140 degrees Fahrenheit). The
growth rate of bacteria is influenced heavily by temperature as seen in these graphs from our
model.
Our model displays the
growth and consumption patterns of bacteria in the human bloodstream. Throughout the human bloodstream and elsewhere
bacteria move, obtain food and reproduce.
Bacteria are carried long distances by air and water currents. Clothing, utensils, and other objects also
carry bacteria. Various kinds of
bacteria have flagella (thin hairs) that enable them to swim. Some species that don’t have flagella move by
wriggling back and forth. Bacteria
obtain food through several different methods, as well. Most kinds of bacteria, called heterotrophic
bacteria, feed on other organisms. Some
species, known as autotrophic bacteria, manufacture their own food. For example, bacteria involved in
photosynthesis in plants make food from carbon dioxide, sunlight, and
water. Certain bacteria may be autotrophic
or heterotrophic, depending on the food available. The majority of heterotrophic bacteria feed on dead
organisms. Others are parasites. Some parasitic bacteria cause little or no
harm to the host organism, but others cause diseases.
In Relation to the Model:
In our model, bacteria reproduce or die at a
certain rate in the human bloodstream according to several specific
factors. The real-life processes by
which bacteria reproduce are more complex.
Most bacteria reproduce asexually.
That means that each cell simply divides into two identical cells by a
process called binary fission. Most bacteria also reproduce quickly, and some
species double their number every 20 minutes.
If one of these cells were given enough food, over a billion bacteria
would be produced in 10 hours.
Industrial and laboratory processes often produce such enormous numbers
of bacteria. But in nature, bacteria lack an adequate food supply to maintain
such a high rate of reproduction.
Food
In
today’s society we are faced with many numerous dangerous health issues. One
concern is the problems that arise involving contaminated foods and food
poisoning. In order for us to survive, food must be consumed daily. With this
in consideration a chance for someone to be exposed to deadly bacteria found in
foods is possible.
Pathogens are bacteria that cause diseases. Food-borne
illness is present when certain pathogens enter the food supply. Studies show
that most cases of food-borne illness are preventable. Proper cooking and
processing of foods will increase the chances of preparing foods that do not
have bacteria. (1)
When showing the likely dangers of eating foods that are
contaminated, the proper information about which foods and why this is
occurring so frequently asked. Awareness of the potential bacteria found in
many fruits, vegetables, meats, and dairy products is beneficial to everyone.
Eleven of the most frequently contaminated organic foods
are strawberries, green peppers, spinach, peaches, (Mexican) cantaloupe,
celery, apples, apricots, green beans, (Chilean) grapes, and cucumbers. (4)
Congressman Sherrod Brown addressed the issue of
contaminated foods in a current article. For example, “two years ago, a Michigan
woman’s ten-year old daughter was infected with Hepatitis A after she ate
contaminated strawberries from Mexico,” stated Brown. A common response as to
why is this happening is dependant upon the proper cleaning and cooking.
81 million cases of food-borne illness occur each year
and 9,100 of these cases result in death; as found by General Accounting Office
(GAO). (3)
Since bacteria multiply rapidly between 40* & 140*,
keeping cold food cold and hot food hot will keep it out of the “danger zone”.
A few of the most common food-borne illness include E. coli, Salmonella, and
others such as Campylobacter.
E. coli is an infectious organism found in hamburger meat
that is contaminated. When eaten, many of the organisms are neutralized by
stomach acid. Depending on the number, the bacteria colonize and produce the
toxin. Potential deadly blood and
kidney damage may be produced. The
sickness begins. People with immune deficiencies, young children, and the
elderly are typically the ones who become extremely ill. (5)
Salmonella is transmitted through raw or uncooked eggs,
meat, and poultry; raw milk, dairy products, and seafood. Within 6-48 hours
after eating, stomach pain, diarrhea, and other symptoms occur.
Another bacteria that is harmful is Campylobacter. Symptoms include fever, muscle pain followed
by diarrhea, and others. It can possibly last up to 10 days. It is found in
contaminated water, raw milk, raw or under cooked meat, and poultry. This
bacterial infection although usually mild can cause a weakness of the
peripheral nerves that lead to paralysis or death. (1)
“Food-borne
illness is one of the most common, yet most preventable of mankind’s ailments,”
says epidemiologist Dr. Robert South of the Lee County Health Department. (2)
Prevention
1.
Careful hand washing and washing produce
2.
Cooking foods thoroughly is critical
3.
Refrigerate promptly
4.
Avoid cross-contamination
5.
Clean up carefully using hot water and soap
In Relation to the Model:
Beginning with the
Food/pop converter, it is Bacteria/1000 which means 1000 bacteria will consume
1 food unit in an hour. Consumed food is the food that is taken in or eaten in
an hour. Food is the supply of food that is available to consume. Food Fraction
is Food/100. This converter transforms
the amount of food left in the system to a decimal fraction to limit the size
of bacteria population. The initial amount of food remains at 100 units. The
important idea is that bacteria increases.
The food supply is getting lower since bacteria is feeding off the
food.
Toxic Limits
Some bacteria are
necessary in order for any individual to survive. This bacteria is found within the human body. There are some bacteria that produce toxins,
which are harmful to the human body.
Toxins are substances, which are poisonous, or chemicals that irritate
or kill. At the chemical level there
are two types of bacterial toxins, which are lipopolysaccharides and proteins,
which may be released into the extracellular environment of pathogenic bacteria
(Proteins Toxins).
There are three ways in
which bacteria can produce toxins:
1)
The bacteria dies and breaks up in the human
gut. This take some time and the
patient starts to feel sick in about 18 hours after the eating the contaminated
food. This type is called an
endotoxin. One example is Salmonella.
2)
The bacteria forms spores when the conditions are
not suitable for growth. They might do
this in the stomach or gut, or when food is being reheated. The affects are felt after about 12
hours. Clostridium perfringens is one
example.
3)
The bacteria grows and multiplies in the food that
a person is about to eat within favorable conditions. This is an exotoxin because the toxin is released outside the bacteria
and produced in the food. It is usually
heat resistant and quick acting. A
person is affected within 30 minutes to 6 hours (Bacterial Toxins).
Bacterial protein toxins
are the most powerful human poisons and retain high activity at very high dilutions. The protein toxins resemble enzymes because
Like enzymes, bacterial exotoxins: 1) are proteins, 2) can be manipulated by
heat, acid, proteolytic enzymes, 3) have a high biological activity and 4)
display specific actions or tasks (Protein).
Certain protein toxins have very specific cytotoxic
activity, where they attack specific types of cells. For example, tetanus and botulinum toxins attack only
neurons. But other toxins, such as
staphylococci, streptococci, and clostridia, have fairly broad cytotoxic
activity and cause nonspecific death of all sorts of cells and tissues,
eventually resulting in necrosis (Protein).
There
are some bacterial toxins that bring about death to living creatures known as
lethal toxins. Although the tissues
affected and the target sites may be known, the precise mechanism by which
death occurs is not understood. An
example is anthrax toxin (Protein).
Protein
toxins are inherently unstable; in time they lose their toxic properties but
retain their antigenic ones. Ehrlich
gave them the term toxoid, which is detoxified toxins, which retain their
antigenicity and their immunizing capacity.
Treating toxins with a variety of reagents including formalin, iodine,
pepsin, ascorbic acid, and ketones can accelerate the formation of
toxoids. The mixture is maintained at
37 degrees at pH range 6 to 9 for several weeks. The resulting toxoids can be used for artificial immunization
against diseases caused by pathogens where the primary determinant of bacterial
virulence is toxin production. Toxoids
are the immunizing agents against diphtheria and tetanus that are part of the
DPT vaccine (Protein).
In Relation to the Model:
Bacteria produces toxins that emit into the human
system. The model shows the bacteria
mainly as a pathogen that is attacking the human body. In the closed system, which is the human
body, organisms such as bacteria metabolize food and excrete waste materials into the body. After a while the amount of waste will
increase to the point where the body system will poison the organisms, or
bacteria living within.
Graph
Temperature
In order for bacteria to
thrive, certain conditions must be present.
Bacteria need food, moisture and most importantly, ideal temperature
conditions. Bacteria rarely
survive in conditions below 4 degrees Celsius and above 60 degrees
Celsius. In order to keep bacteria from
growing temperature must be controlled.
When body temperature rapidly increases, bacteria levels begin to
decrease. An example of this is when
you are sick. Your body warms up causing a fever. This fever is the body’s way of fighting off unnecessary amounts
of bacteria.
The optimum growth for bacteria
in the human body is 98.6. Basically,
there is a certain temperature span that must be present in order for bacteria
to survive. If it is too cold or too
warm the bacteria will be unable to survive.
In Relation to the Model:
In our model we set one of our graphs at 90 degrees. At 90 degrees the bacteria thrived. This temperature is closely related to the
98.6 degrees of the human body. In
contrast, we also set a graph at 85 degrees.
This temperature was too cold for the bacteria and it dramatically
decreased.
Blood pH - Does it affect bacterial growth?
First
we must understand pH before we can determine the answer to this question. Webster’s
New World Dictionary defines pH as
[potential
of Hydrogen], the logarithm of the reciprocal of the hydrogen ion concentration,
expressed in gram atoms per liter of a solution, and used to indicate acidity
or alkalinity; pH 7 (0.0000001 gram atom of hydrogen ion per liter), the value
of pure water, is regarded as neutral; pH values from 0 to 7 indicate acidity
and pH values from 7 to 14 indicate alkalinity (Webster 1096).
According
to the MERCK Manual of Medical
Information, the pH of our blood normally remains in the very small range
of 7.35-7.45. Humans are very sensitive
to changes in pH levels and if these levels rise above 7.8 or fall below 7.o,
death will occur. Our body has a very
good buffering system to prevent this from happening. Regulation of pH can be seen through three different
methods. The most obvious way that our
bodies regulate the acid levels in our bloodstream is through the kidneys. The kidneys remove excess acid and excrete
it as ammonia in our urine. Another way
that our pH is controlled is by the bicarbonate and carbon dioxide that already
exists in our bloodstream. When the
blood becomes too alkaline for some reason, we produce more carbon dioxide,
which brings the pH back down. If our
blood becomes acidic, we produce more bicarbonate, bringing the pH back
up. The last way that we can adjust our
pH is through our respiratory system. If
the blood becomes too alkaline, the respiratory control centers in the brain
are stimulated, causing the person to breathe more slowly and deeply, causing
carbon dioxide levels in the blood to increase, lowering the pH. If the blood becomes acidic, the respiratory
centers are stimulated to make the person breathe more rapidly, expelling more
carbon dioxide, causing a decrease in carbon dioxide levels in the blood,
raising the pH.
What
causes our pH levels to fluctuate? The MERCK
Manual also outlines some of the causes for fluctuations in pH. Too much acid in the blood is a condition
known as acidosis. This can be a result
of the ingestion of wood alcohol, antifreeze, or an overdose of aspirin. It can also be a result of illness such as
type I diabetes, emphysema, chronic bronchitis, pneumonia, or asthma. Too little acid in the blood results in a
condition called alkalosis. Alkalosis
can result from hyperventilation or extended periods of diarrhea or vomiting
(MERCK 676-679).
In Relation to the Model:
Now that we know a little
something about pH, we can get back to the question of how does pH relate to
bacterial growth? The answer is, is
that pH alone really does not have any effect on bacterial growth in our bloodstream. Instead, it turns out that the bacteria have
more of an effect on our pH than the pH has on it. Bacteria cause the bronchitis, pneumonia, vomiting and diarrhea
that result in acidosis and alkalosis. Because we have such a small window of
pH (7.0-7.8) in which we can exist, it turns out that we cannot survive a pH
change that is big enough to affect bacteria growth. A change in pH in combination, with a change in temperature and
toxic limits, will have some affect on bacterial growth, but pH alone cannot
make a difference.
Graphs