Two streptococcus pneumonia strains, agent 1 and agent 2, are administered to groups of animals at...

Two streptococcus pneumonia strains, agent 1 and agent 2, are administered to groups of animals at different doses. Mortality rates are then measured for the animals that received each dose level of each agent. Agent 1 found to have an LD50 of 400. Agent 2 was found to have an LD50 of 600.

a) Which one is producing a capsule and which one is not? Why?

b) Briefly explain 2 ways in which bacterial capsules facilitate host colonization and pathogenesis.

Solutions

Expert Solution

a) Since LD50 of agent 1 is lower, the agent 1 is more virulent as there is inverse relation between LD50 and virulence.
Presence of capsule makes the bacteria more virulent as it prevents their phagocytosis and help in adherence to the host cell. This means that the agent 1 is producing capsule and agent 2 is not.

b) 1. Capsule contain large amount of water which it turn exclude the viruses and hydrophobic toxins. This prevents the killing of bacteria by desiccation and makes it more pathogenic. Presence of capsule also prevents the phagocytosis of bacteria from the cells of the host's immune system and thereby ensure its pathogenicity.
2. The glycocaclyx of capsule serve to help the bacteria to adhere to the tissue surfaces in the host body.

gladiator answered 1 year ago

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