The famous experiment by Avery, MacLeod and McCarty showed that neither heat killed S-type nor live R-type pneumococci could kill mice (experiment 1) but simultaneous injection of both killed the mice just as efficiently as the live S-type (experiment 2). S-type pneumococci are known to possess a capsule structure outermost to the cell wall. Structurally, capsule is a linear homopolymer of sialic acid residues. Apart from the capsule, there are other virulence factors present in these bacteria such as adhesion proteins that recognise a wide range of molecular motifs and provide targeting of the bacteria to specific tissue surfaces in the host. |
(I) one can hypothesise that sialic acid residues are likely to be poorly immunogenic if the same homopolymer is a structural component of the host. |
(II) If the capsular deficient mutants are used in place of S-type bacteria and adhesion deficient mutants in place of R-type in the Avery, MacLeod and McCarty experiment, mice would be killed. |
(III) If genomic DNA from S-type is extracted and injected sub-cutaneously into the mice, most of the mice would be killed. |
(IV) In the experiments performed by Avery, |
MacLeod and McCarty, all types of live R strains recovered from dead mice would also be virulent. |
Select the option with true statements. |
A) (I) only
B) (I), (III) and (IV)
C) (III) only
D) (I) and (II)
Correct Answer: A
Solution :
Because these capsules are structurally similar to polysaccharides encountered on host tissue, these capsules are poorly immunogenic, and elicit a poor antibody response in the host.You need to login to perform this action.
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