Question

You are studying diseased mouse using Koch's postulates. You isolate two microbes that you think may be responsible for the disease. You observe the individual organisms under a microscope and do some molecular tests and record your results in the table below. Peptidoglycan Glycosidic Slime Capsule Fimbr crosslink bond layer organism Direct SS-1,3 PresentAbsent Abser crosslink OrganismInterbridge SS-1,3 Absent Present Abser Based on the provided information which of the two strains would you test first using Koch's remaining postulates?

Answer 1

• Robert Koch, formulated certain steps to establish relationship between the causative agent and the disease.

Koch postulates included:

• The diseased condition should be assotiated with abundance of microorganisms or pathogens, while a healthy individual should have much lesser number of the organisms.
• The causative agent should be isolated from the diseased individual and cultured as pure culture.
• If the same cultured organism is re-introduced into a healthy individual, it should cause the same disease.
• The pathogen thus introduced into the experimental host should be re-culturable.

• As per the observation, bacterial strain A contains slime layer and strain B contain capsule.
• Both slime layer and capsule are glycocalyx layers present outside the cell wall of bacteria.
• However, slime layer has loosely attached, while capsule have tightly associated glycoproteins.
• Also, slime layer may be easily washed off, but capsules are more firmly attached.
• Considering virulence factor, capsule can evade phagocytosis. Slime layer mainly helps in cell adhesion.
• Thus, strain B will be more sutable to test Koch postulates as capsule is present in these cells.