Erythrocytes sensitized with antigens are called
Answer: A
Correct answer: erythrocytic diagnosticum
Red cells coated with a known antigen make an erythrocytic diagnosticum: they clump visibly when the corresponding antibody is present, so a reaction too fine to see becomes a plain agglutination. The technique is indirect (passive) haemagglutination, and the red cell serves only as an inert carrier.
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The interaction between somatic antigens and specific antibodies is
Answer: A
Correct answer: slow and fine granular sediment forms in 18-20 hrs. agglutinate do not break upon shaking
Somatic (O) antigens are lipopolysaccharide, lying on the cell surface itself, so the cells are drawn tightly together: agglutination is slow, the deposit is fine and granular, and it does not redisperse when shaken. Flagellar (H) agglutination is the opposite - rapid, loose and flocculent, and easily broken up.
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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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H antigen is a
Answer: C
Correct answer: flagellar antigen
H is the flagellar antigen, from the German Hauch, the spreading film that motile organisms make on a plate. It is protein - flagellin - and heat labile, unlike the O antigen, which is polysaccharide and heat stable.
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Which one of the following statements about endotoxins is false?
Answer: C
Correct answer: action is often enzymatic
That statement is false. Endotoxin is the lipid A of lipopolysaccharide, and it acts not as an enzyme but by triggering the host’s own inflammatory cascade - the cytokines that produce fever and shock. Exotoxins are the ones with enzymatic action. The other three statements are true: endotoxin is heat stable, it is a lipopolysaccharide-protein complex, and it comes from gram-negative bacteria.
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Primary infection is
Answer: A
Correct answer: initial infection with organism in host
A primary infection is the first infection of a host by a given organism. A reinfection is a later one by the same organism, and a secondary infection is a new one by a different organism in a patient already weakened by disease.
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The attachment structures of bacteria are the
Answer: D
Correct answer: all of the above
All three are names for the structures by which bacteria stick to a surface. Fimbriae and pili are the short hair-like appendages themselves - the words are often used interchangeably, though pilus is also used for the longer sex pilus - and colonisation factors is the general term for the adhesins that let a pathogen attach to a particular host tissue. Attachment is the first step of almost every infection.
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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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Which one of the following statements about exotoxins is false?
Answer: D
Correct answer: polysaccharide-lipid complex in nature
That statement is false: exotoxins are proteins. It is the endotoxin that is a lipopolysaccharide complex. The other three are true of exotoxins - their action is usually enzymatic, they have specific tissue affinities (tetanus toxin for nerve, cholera toxin for gut epithelium), and being catalytic they are active in minute amounts. Being protein, they are heat labile and can be converted into toxoids.
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Cross infection is
Answer: C
Correct answer: situation, when patient suffering from a disease and new infection is set up from external source
A cross infection is a fresh infection acquired from an outside source by a patient already ill with something else - classically in hospital, where it is called a nosocomial or cross infection. A first infection by an organism is a primary infection, and a later one by the same organism is reinfection.
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