Epidemic disease is
Answer: B
Correct answer: spreads rapidly, involving many persons in an area at the same time
An epidemic is an outbreak affecting many people in one area at one time, well above the expected level. A disease constantly present at a low level is endemic; one spreading across many countries is a pandemic.
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The antigen causing agglutination is called
Answer: A
Correct answer: agglutinogen
The agglutinogen is the antigen; the agglutinin is the antibody that clumps it; and the agglutinate is the visible clump they form. The parallel set for precipitation is precipitinogen, precipitin and precipitate.
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Fixation of the smear is necessary for
Answer: D
Correct answer: all of the above
Fixing serves all three purposes: it kills the organisms, making the slide safe to handle; it makes them stick to the glass so they are not washed off during staining; and it alters the cells so that they take up the dye more readily.
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Flagella are demonstrated by
Answer: D
Correct answer: Morozov’s staining
A flagellum is far too thin to see by ordinary light microscopy, so it must first be thickened. Morozov’s silver impregnation deposits metal along it until it is visible - the same principle as the mordant-and-silver flagella stains generally.
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Bacteria that cannot grow in the presence of oxygen are
Answer: A
Correct answer: Strict anaerobes
Strict (obligate) anaerobes are killed by oxygen, because they lack the enzymes that dispose of the toxic products of oxygen chemistry. Strict aerobes require it; facultative anaerobes grow with or without it; microaerophiles need it but only at low concentration.
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Naked viruses are
Answer: B
Correct answer: Nonenveloped
A naked virus is simply one with no envelope - the capsid is its outermost layer. Such viruses are the tougher: having no lipid, they survive drying, detergents and the acid and bile of the gut, which is why so many of them spread by the faecal-oral route.
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Growth factors are
Answer: D
Correct answer: Essential substances that bacteria cannot synthesise for themselves
A growth factor is an organic compound - a vitamin, amino acid, purine or pyrimidine - that an organism must have but cannot make, so it has to be supplied in the medium. Mineral salts and the bulk elements are nutrients, but they are not growth factors.
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Which of the following is a simple staining method
Answer: D
Correct answer: Burri
A simple stain uses a single dye and shows shape and arrangement without distinguishing types of cell. Burri’s India-ink method is of that kind - strictly a negative stain, colouring the background rather than the cell. Gram, Neisser and Ziehl-Neelsen are all differential stains, using more than one reagent to separate one group of organisms from another.
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The covalent bond which links the cell walls of gram-positive bacteria containing two modified sugars - N - acetylmuramic acid (NAM) and N-acetyl glucosamine (NAG) is
Answer: B
Correct answer: 1,4-glycosidic bond
The glycan backbone is an alternating chain of NAM and NAG joined by β-1,4-glycosidic bonds - the same linkage as in cellulose and chitin. It is precisely this bond that lysozyme hydrolyses, which is why tears and saliva can lyse many bacteria.
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The function of an adjuvant in a vaccine is
Answer: C
Correct answer: antigenicity
An adjuvant makes the antigen more immunogenic: it holds the antigen at the injection site so that it is released slowly, and it provokes a local inflammatory response that draws in and activates antigen-presenting cells. The result is a stronger and longer-lasting response to the same amount of antigen.
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