1. JonathanJeffrey
5/3/15
LIFE 205
Microbial Biology
Assignment #5
Total Points: 20
Postedto Ram Blackboard:Wednesday, April 29, 2015
Due Date: Monday, May 4, 2015;At the beginning of class:
See Note Below*
Instructions:
Utilize lecture material and the reading from your text “Microbiology A Human Perspective” to
answer the questions. Each question can be answered with a few sentences or a short paragraph.
Answers should be concise, complete, and clearly written.
Write each question and then give your answer. The assignment must be typed, single spaced,
and in 12 font. Your answers should have a double space between each question.
You must turn in a hard copy of the assignment in class on due date, May 4, 2015.
No e-mailed copies will be accepted.
*NOTE: The assignment is due at the beginning of class on the due date. It will be considered
late and a 2-point deduction will be taken if the assignment is turned in after 2:05 p.m. on
the due date. You will lose an additional 2 points for every day the assignment is late.
This assignment will NOT be accepted for any reason after 2:05 p.m. Friday, May 8, 2015.
Questions for Chapters 24, 25, 26, 27, 28, 29, 31
1. Why are new cavities less common, but loss of teeth more common in people over
65? (1.0 pts)
New cavities are less common in older groups because the pits in the teeth where cavity
forming caries lives wear down with time and the bacteria have less places on the teeth to
live. Older people are more likely to have receding gums that expose more tooth surface
area where tooth decay can take place. When the bacteria are able to get closer to the root
of the tooth, the plaque that forms there releases tissue degrading enzymes and is more
likely to cause the tissue surrounding the root to decay, causing the tooth to fall out.
2. Give two ways in which the chancre of chancroid differs from the chancre of
syphilis. What, if any, is the relationship between chancroid and development of
AIDS? (1.5 pts)
The chancre of syphilis is a painless red, hard ulcer. It may be on the genitals or
elsewhere. It causes enlargement of the local lymph nodes. Chancres of syphilis can be so
small they go unnoticed or they can be absent altogether. Chancres of chancroid are

2. characterized by one or more painful genital sores that are soft, tender, and full of pus.
They begin as a pimple at the site of infection and ulcerate. They may rupture,
discharging the pus. They can also occur on the thighs. Chancroid chancres are lesions
and a sign of sexually transmitted disease. This is an indicator of high levels of sexual
activity, which increases the risk of HIV transmission, and lesions always increase the
risk of transmitting or contracting HIV.
3. Why does shigellosis cause dysentery, and cholera causes watery diarrhea? (2 pts)
Cholera is caused by the bacteria Vibrio cholera colonize in the small intestine on the
epithelium, multiplying and producing cholera toxin, this enterotoxin activates ion
transport channels in the epithelial cell membrane, causing chloride and other electrolytes
to exit the cells. Water follows the electrolytes, causing an influx of water and salts in the
intestinal lumen. The volume of fluid is too great to be reabsorbed by the large intestine,
causing severe diarrhea. Shigellosis causes dysentery because colonization of the bacteria
Shigella dysinteriae on the epithelium of the intestine causes cell death after the
bacterium infect the cells of the epithelium, the patches of infected cells slough off and
leave exposed inflamed patches, covered in pus and blood that cause the symptoms of
dysentery.
4. What are possible consequences of sexually transmitted papillomavirus infections
for men, women, and babies? (1.5 pts)
Possible outcomes of HPV in men are warts on the penis, or anus, and different types of
lesions caused by the warts, they can also cause penile anal and oral cancer. In women,
warts can occur at the vaginal opening or inside the vagina, cause blockage of the urethra,
or cause cervical, anal, or oral cancer. In newborn babies, HPV can cause warts that
cause blockage of the respiratory tract, and can be a very serious problem.
5. What is the difference between HIV, HIV disease, and AIDS? What role do
asymptomatic people with HIV disease play in the epidemiology of AIDS? (1.5 pts)
HIV is human immunodeficiency virus. It is the virus that causes HIV disease and AIDS.
HIV infection just indicates that the virus is present in the body and may not be causing
any signs or symptoms. HIV disease indicates that the virus is beginning to cause
symptoms. Symptoms look like many other viral infections may be flulike and include
headache, fever sore throat, and muscle aches. This stage is characterized by high levels
of viral replication, followed by a possible latency period that can last years. During this
latency period the virus is still replicating however, and causes cell damage and death and
therefore can be asymptomatically transmitted to other people, a dangerous factor in the
epidemiology of the disease. AIDS is the last stage of the disease and is characterized by
low CD4 lymphocyte levels and the presence of opportunistic infections and fever weight
loss, fatigue and diarrhea, and persistent enlargement of the lymph nodes.
6. Why might rodent burrows be a source of plague months after they are abandoned?
How would conditions in crowded cities favor spread of plague? (1 pt)
Rodent burrows could contain plague even months after abandonment because the
bacteria is present in fleas that infect the rodents. The fleas can remain infectious for a
year or even more and are likely to be present in the rodents den. Crowded cities can be a

3. reservoir because they provide places were infected rodents can thrive, and food sources
for them, too. The fleas can also spread between people because of the dense population
of people. In some Chinese provinces, earthquakes can create conditions for reservoirs of
plague to thrive.
7. What is the difference between sporadic encephalitis and epidemic encephalitis?
Name one cause of each. (1.5 pts)
Epidemic viral encephalitis is spread through populations through insect bites. It is
usually caused by arbovirus, a group of enveloped, single stranded RNA viruses
transmitted by insects, mites, or ticks. Sporadic encephalitis is usually due to the
reactivation of latent viruses. Herpes simplex virus usually causes sporadic encephalitis.
8. Why might clots on the heart valves make microorganisms there inaccessible to
phagocytic killing? (1 pt)
If a clot has formed on a deformed heart valve, microbes can get trapped there, because
of the disrupted blood flow. The microbes create a biofilm at the site which protects them
from phagocytic killing. The clot grows larger around the organisms and bacteria fall off
the mass into circulation.
9. Why is rabies now rare in humans when it is still so common in wildlife? What
animals most commonly carry the rabies virus? (2.0 pts)
Rabies is rare in humans because it is most commonly transmitted to humans through dog
and cat bites. We now vaccinate all domestic dogs and cats against the rabies virus, so
they cannot carry it. If a human is infected, they can be vaccinated as well. The most
common animal carriers of the rabies virus are raccoons and skunks.
10. Explain the typical sequence of events that lead to staphylococcal food poisoning.
Why would S. aureus more likely be found in higher numbers on ham than on fresh
meat? (2 pts)
Typically, a person with poor hygiene transmits S. aureus handles a food that has proper
growing conditions for S. aureus. Proper growing conditions include moist rich foods in
which other organisms have been killed or their growth inhibited. Ham, for example, is a
better S. aureus carrier than fresh meat because it has been treated and salted to kill other
potentially competitive organisms, and refrigerated to inhibit the growth of new
organisms. Once the organism inoculates the food, and the food is left at room
temperature, the organism multiplies, producing the exotoxin. The exotoxin is heat stable,
so cooking it will not destroy the toxin. Food poisoning occurs when the toxin is already
present in the food and is ingested.
11. Why do lakes in temperate regions stratify during the summer months? (1.5 pts)
In summer months, the surface water turns warm, decreasing the density of the surface
water. This forms a separate layer from the cooler water below. The upper layer is
referred to as the epilimnion, is rich in oxygen from photosynthetic activity. The colder
layer, the hypolimnion may be anaerobic because of oxygen consumption by
heterotrophs.

4. 12. Why are prokaryotes critical in the nitrogen cycle? What is the importance of
nitrogen fixation? (1.0 pts)
Prokaryotes are diverse in their use of nitrogen containing compounds. Some use nitrite
and nitrate as terminal electron acceptors. Others use ammonium as energy sources.
These activities are essential in the nitrogen cycle. Nitrogen fixation is the process in
which nitrogen gas is reduced to make ammonia, which can be incorporated into cellular
material. The process is catalyzed by nitrogenase. Very few organisms, almost all
prokaryotes, are able to reduce this abundant gaseous form of nitrogen. Humans and
other animals rely on prokaryotes to convert nitrogen gas to the usable form for creation
of biomass.
13. Why are ground meats more common than steaks as a source of E. coli O157:H7
infection? (1.5 pts)
Initial infection of meat occurs on the exposed surface that is cut, and can be seared off
during cooking. When the surface area of the meat is ground into itself, as with ground
beef, the bacteria that the surface has been exposed to is churned throughout the beef, and
must be cooked all the way through to kill the bacteria.
14. Why is dengue feverknown as “break-bone” fever? Why is a second infection with
dengue virus more serious than the first? (1 pt)
Dengue fever is called break-bone fever, because it causes severe joint and muscle pain.
A second infection is generally more serious because dengue hemorrhagic fever and
dengue shock syndrome can occur because antibodies to the original strain of the virus
already exists. When a different strain is introduced, antibody dependent enhancement
(ADE) of the virus occurs. Preexisting dengue antibodies recognize the virus in the
second infection and form complexes that instead of inhibiting the virus actually facilitate
the entry of the virus into cells that express Fc receptors, where the virus freely replicates
causing more infected cells and a more severe infection.