Suggested Answers for Insight Questions, Foundations in Microbiology, 7th Edition, listed
by chapter, number, and page location.
A note to the users of these answers: These answers discuss some of the possible ways to
approach the questions. They are not meant to be exhaustive in depth, but can offer information,
suggestions, and points of view that will be helpful in understanding some of the concepts
covered in the Insight and the chapter. Furthermore, they are not the final word--you may have
thought of some other explanations that are just as valid. It is hoped they will serve to stimulate
class discussion and inspire further research.
13.1, pg. 390 – Life Without Flora
The earliest flora of a fetus are acquired before the actual birth process, when the amniotic sac
inside the uterus begins to tear. Microbes that live in the mucosa of the cervix, vagina, and
external reproductive regions can potentially find their way through the weakened cervix into the
uterus. Mostly these are normal flora of the mother, but they can still establish themselves in the
fetal skin, membranes, and GI tract. The birth process exposes the newborn even more, since it
comes in such close contact with the vaginal membranes and is exposed to adults in various
ways from birth on. Once any microbes have reached the fetus or newborn, it can never be
made sterile again. So, a controlled birth is necessary prior to the weakening or breakage of the
amniotic sac, and the uterus is opened through an incision in the mother's abdomen, with the
newborns taken by sterile hands and placed immediately into sterile isolators.
13.2, pg. 392 – Laboratory Biosafety Levels and Classes of Pathogens
Based on our own labs, we use only microbes in levels 1 and 2. Micrococcus, Bacillus,
Lactobacillus, and Saccharomyces are considered harmless, and infections by these agents are
non existent or extremely rare. We usually use the less pathogenic species earlier in the
semester while students are still learning to use aseptic techniques. Then we introduce some
class 2 pathogens around midterm, including Salmonella and Shigella, but we use the less
pathogenic members of these genera. We also restrict our use of true pathogens to enteric
pathogens, since they generally are not transmitted in air. We don't use any pathogenic worms,
viruses, or fungi. When we use Corynebacterium diphtheriae, Staphylococcus aureus, and
Escherichia coli, they are strains that have been modified for reduced pathogenicity. The class 3
and 4 pathogens are far too virulent for most teaching labs and may be spread readily by air. A
professor of mine once said that everyone in his research lab eventually got tularemia (caused by
Franciscella tularensis) when he was working for in a pathogens lab. It is very infectious, with a
small dose and several portals of entry.
13.3 pg. 395 – Human Guinea Pigs
The main reason was that pathogens were known to have different effects on animals and
humans. Some pathogens, such as viruses, are quite species specific, and would not normally
infect a test animal. Examples are hepatitis B virus and mumps virus. Another reason was that
the microbe could infect the animal, but either did not cause a disease or did not cause the same
disease that humans acquired. Syphilis and leprosy are examples of this effect. Some
infectious agents may vary greatly in their infectious doses between humans and animals. Other
infectious agents may have different portals of entry and exit in animals and humans. Of course,
we simple would not purposely infect humans with these diseases anymore. We have to acquire
knowledge through study of existing cases and indirectly through animal models.
13.4, pg. 401 – A Quick Guide to the Terminology of Infection and Disease
Urethritis is an inflammatory condition of the urethra in males or females. It is usually due to an
infection; for example, chlamydia is the cause of non-gonococcal urethritis in males.
Endotoxemia means the presence of endotoxin in the blood. It usually arises when a patient has
a blood infection with gram-negative bacteria, and the lysis of the bacterial cell wall releases the
endotoxin into the bloodstream. Chlamydiosis is an infection by the genus Chlamydia. It is
usually an STD and may lead to scar tissue in the reproductive tract and infertility. Lymphoma is
cancer of a lymph node. It is one of the illnesses that commonly strikes AIDS patients.
13.5, pg. 414 – Koch’s Postulates: Solving the Puzzle of New Diseases
Epidemiologists and the world's medical community are convinced that HIV is the established
cause of AIDS, largely based on the combined research and statistics accumulated for human
cases over nearly 30 years. Tracing the disease from initial infection to full blown AIDS and
tracing the virus loads during these stages has been accomplished hundreds of thousands of
times, with predictable results. No patients with full blown AIDS symptoms have ever tested
negative for the virus. Drugs that act on HIV replication cycle are able to lower virus levels and
hold the disease at bay, returning relative health to most people who take the drugs. There is no
doubt that HIV is transmissible, and it has been documented on film lysing its host cells during
viral release. Consider just the example of hemophiliacs alone. This population began to acquire
AIDS early in the epidemic. Their infection was traced to a blood product, factor 8, taken from
unsterile pooled serum they took for their disease. The virus was found in this product. Infection
and AIDS had killed nearly 50 % of hemophiliacs by the 1990s. Many of these hemophiliacs
transmitted this virus to their wives or female sex partners, who developed AIDS. A number of
these women become mothers and transmitted the virus to their fetus, who also got AIDS. The
few naysayers who say that AIDS is not caused by HIV claim that life style choices and drug
abuse cause AIDS, and the virus is just "along for the ride". The statistics listed on page 771
should be enough evidence for a reasoning person.