question_answer

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)