Bauman Chapter 19 Answers to Critical Thinking Questions
p. 555
Why must diphtheria and tetanus vaccines be boosted every 10 years?
Diphtheria and tetanus vaccines are inactivated toxin extracts with few antigenic
determinants. Immunogens with few antigenic determinants do not generate lasting
immunity.
p. 559
Why don’t physicians try to prevent the spread of TB by simply administering
prophylactic antimicrobial drugs to everyone living in endemic areas?
Preventing TB with prophylactic administration of antibiotics is not practical logistically or
economically: Experts estimate that about one third of the world population is infected
with M. tuberculosis, and billions of people (on the order of 2/3 to 3/4 of the world
population) would need to be vaccinated, at prohibitive cost. In addition, such
widespread antibiotic use could result in rampant development of antibiotic resistance.
Finally, less than half of patients immunized against TB develop immunity, but all will
show a positive tuberculin test in the future, making it more difficult for epidemiologists to
monitor the incidence, prevalence, and spread of the disease.
p. 565
1. In Chapter 4 (p. 121) we discussed the identification of microbes using dichotomous
taxonomic keys. Design a key for the genera of Gram-positive cocci discussed in
this chapter. Design a second key for identifying the Gram-positive bacilli discussed
in the chapter.
Catalase?
Yes
No
Hemolytic?
Staphylococcus
Yes
Streptococcus
No
Enterococcus
Yes
Endospores?
Strict
anaerobe?
Filamentous?
Yes
No
Clostridium
Bacillus
Yes
No
Cords?
Yes
Mycobacterium
No
Acid-fast?
Yes
2.
No
Cold
tolerant?
Actinomyces
No
Nocardia
Yes
Listeria
No
Snapping
division?
Yes
No
Corynebacterium
Propionibacterium
A few days after the death of a hospitalized child from an MRSA infection, another
child, who had been admitted to the hospital with viral pneumonia, worsened and
died. An autopsy revealed that the second child also died from complications of
MRSA. By what route was the second child likely infected? What should hospital
personnel do to limit the transfer of MRSA and other bacteria among patients?
Methicillin-resistant Staphylococcus aureus (MRSA) can colonize the skin, and the
second child was likely infected by contact with the skin or hands of a hospital worker.
Hospital personnel need to be diligent about washing their hands before touching a
patient, and surfaces that may be contaminated by skin contact need to be disinfected
as frequently as is practical.
3.
An elderly man is admitted to the hospital with severe pneumonia, from which he
eventually dies. What species is the most likely cause of his infection? What
antimicrobial drug is effective against this species? How could the man have been
protected from infection? Is the hospital staff at significant risk of infection from the
man? Which groups of patients would be at risk if the man had visited their rooms
before he died?
Streptococcus pneumonia is a frequent cause of potentially fatal pneumonia in the
elderly. Erythromycin and cephalosporin are effective against S. pneumonia, and most
strains are still susceptible to penicillin. The vaccine Pneumovax provides immunity to
S. pneumonia and may have provided protection to the man, although the elderly do not
always develop protective immunity. The hospital staff is not at great risk of infection as
young and middle-aged healthy adults rarely contract symptomatic infection. Elderly
persons and people with pre-existing respiratory disease would be at risk of infection
had they been exposed to the man before he died.
4.
Botulism toxin can be used as an antidote for tetanus. Can tetanus toxin be used as
an antidote for botulism? Why or why not?
No, tetanus toxin is not an antidote for botulism toxin. Botulism toxin blocks the neuron
signal to muscle cells to contract, producing a flaccid paralysis, while tetanus toxin
interferes with the inhibitory signals that allow muscle contraction; tetanus toxin cannot
counteract flaccid paralysis.
5.
A blood bank refused to accept blood from a potential donor who had just had his
teeth cleaned by a dental hygienist. Why did they refuse the blood?
Cleaning the teeth damages the soft tissue around the teeth, removing a barrier that
otherwise prevents oral flora from entering the bloodstream. For a short period of time
the persons’ blood carries potential opportunistic pathogens from the oral cavity.