A. Gram-negative anaerobic rod
B. Gram-positive cocci
C. Gram-positive anaerobic rod
D. Gram-positive aerobic rod
The correct answer is C. The causative organism of tetanus is Clostridium tetani , which is a gram-
positive, spore-forming anaerobic rod. Bacteroides is gram-negative anaerobic rod (choice A).
Examples of gram-positive cocci (choice B) are staphylococci and streptococci. The causative
organism of anthrax, Bacillus anthracis , is a gram-positive, spore-forming aerobic rod (choice D).
97. Last year's influenza A vaccine is unlikely to be effective today because influenza A
A. has a heavy polysaccharide coat
B. immunosuppresses the patient
C. kills lymphocytes
D. resists inactivation by complement
E. undergoes genetic reassortment
The correct answer is E. The difficulty with developing a vaccine against influenza A arises because
the influenza virus genome is composed of eight strands of single-stranded RNA. Minor shifts
(antigenic drift) in surface antigens that occur as point mutations in the genes accumulate. Influenza A
can also undergo larger, abrupt changes in antigen expression (antigenic shift), however, as a
consequence of reassortment of some of the RNA fragments between human and nonhuman hosts.
Thus, last year's vaccine does not necessarily work against this year's virus. Polysaccharide coats
(choice A) are a virulence factor of some bacteria, not of viruses. Influenza A can compromise the
lungs sufficiently to predispose to secondary infections, producing a functional immunosupression
(choice B), but this attribute does not make it difficult to produce vaccines against the virus. Unlike
AIDS, influenza virus does not selectively target lymphocytes (choice C). Influenza A, bound to
antibody and complement, can be effectively phagocytized (compare with choice D).
98. Infections in hyaline cartilage typically destroy the cartilage because
A. cartilage contains chondroitin sulfate
B. cartilage contains collagen
C. cartilage is not innervated
D. cartilage is relatively avascular
E. cartilage tends to become calcified
The correct answer is D. Hyaline cartilage contains very few, sparsely distributed, small blood
vessels. The tissue consequently is very vulnerable to infection because the immune system (white
cells and serum with clotting factors and antibodies) cannot access the cartilage in an efficient
fashion. Chondroitin sulfate (choice A) is an important constituent of cartilage that can be attacked by
bacteria, but this is not the cause of uncontrollable infections in the cartilage, because if the infection
is controlled, chondrocytes will continue to synthesize chondroitin. Collagen (choice B) is present in
cartilage, but does not predispose the cartilage for uncontrollable infection. Collagen is not innervated
(choice C), but this does not contribute to the development of uncontrollable infection. The tendency
of cartilage to undergo calcification (choice E), even when not acting as the site of ossification, does
not predispose for uncontrollable infection.
99. The highest level of chronic disease state is associated with which of the following
diseases?
A. Hepatitis A
B. Hepatitis B
C. Hepatitis C
D. Hepatitis D
E. None of these diseases have chronic carrier stages
The correct answer is choice C. Hepatitis C is a disease about which much has been learned
recently, but much more is unknown. It seems to be transferred through both bloodborne and sexual
routes (not fecal/oral). It is harder to contract than HBV, but easier than HIV. It is distinguished by
having the highest percentage of cases going into a chronic destructive stage, of all hepatitis types. It
is a single stranded RNA virus. It was formerly known as NANB (Non-A Non-B) or "transfusion
hepatitis" because tests for hepatitis A or B did not detect it. Hepatitis B also has a destructive carrier
state, but it is less common. Hepatitis A has NO carrier state, and exposure to Hepatitis A gives
lifelong immunity.
100. Which of the following organisms would most likely be isolated from the vagina of a
normal 5-year-old girl?
A. Candida
B. Lactobacillus
C. Neisseria
D. Staphylococcus
E. Streptococcus
The correct answer is D. The vagina of prepubertal girls and postmenopausal women is colonized
by colonic and skin bacteria, including Staphylococcus epidermidis, which is normally found on the
skin. The vagina of women of childbearing age tends to be colonized by Lactobacillus (choice B)
species, yeasts such as Candida (choice A), and Streptococcus species (choice E). The presence of
Neisseria (choice C), such as N. gonorrhoeae (the cause of gonorrhea), in the vagina of a 5-year-old
girl strongly suggests sexual abuse.
