Bacteria Questions and Answers

Answer: C

Correct answer: immunoglobulin transfer

Receiving ready-made immunoglobulin gives passive immunity: the recipient’s own immune system never responds, so no memory is left and the protection fades within weeks. Active immunity is what the body builds for itself - after an infection, a subclinical infection, or a vaccination.

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.

Answer: A

Correct answer: attenuated bacteria

A live vaccine contains organisms that have been attenuated - weakened by repeated passage or by mutation so that they multiply in the recipient without causing disease. Because they multiply, the dose is small and the immunity strong and long-lasting; the price is that they must be kept cold and are unsafe for the immunocompromised. BCG and oral polio are examples.

Answer: C

Correct answer: inactivated bacteria

A killed corpuscular vaccine contains whole bacteria inactivated by heat or chemicals. Nothing multiplies, so it is safe and stable but generally needs a larger dose and booster injections. The old typhoid, cholera and whooping cough vaccines were of this kind.

Answer: B

Correct answer: immunogenic component of the bacteria

A subunit vaccine contains only the immunogenic part of the organism - a surface protein or a capsular polysaccharide - and none of the rest. Leaving out everything unnecessary means far fewer side effects; the hepatitis B and pneumococcal vaccines work this way.

Answer: D

Correct answer: inactivated toxin

A toxoid is an exotoxin treated with formalin so that it loses its toxicity but keeps its antigenicity. The recipient makes antitoxin, which neutralises the real toxin on any later exposure. Diphtheria and tetanus vaccines are toxoids, which is why they protect against the toxin rather than against infection itself.

Answer: D

Correct answer: serological reaction with the use of labels

Immunofluorescence is a labelled antibody technique: the antibody carries a fluorescent dye, and binding is read under a fluorescence microscope. It belongs with ELISA and radioimmunoassay, which use enzyme and isotope labels, rather than with the unlabelled reactions of precipitation, agglutination and lysis.

Answer: D

Correct answer: All of the above

Monoclonal antibodies are used for all three: as therapeutic agents, since a single specificity can be directed at one target; for the identification of cells and tissues, as in typing leukaemias by their surface markers; and, radiolabelled, for imaging, localising a tumour by where the antibody accumulates.

Answer: C

Correct answer: tube agglutination

The tube method is the quantitative one: the serum is diluted serially and a fixed amount of antigen added to each tube, so the result is a titre - the highest dilution still giving agglutination. Slide agglutination is quick but only qualitative.

Answer: B

Correct answer: capsular antigen

K is the capsular antigen - from the German Kapsel. The other two in the Kauffman-White scheme are O, the somatic antigen of the lipopolysaccharide, and H, the flagellar antigen. Together they define the serotype of an enterobacterium.