Pure culture of microorganisms was obtained from pharynx of a child with suspected diphtheria. Morphologic, tinctorial, cultural, and biochemical properties of the microorganisms were studied and revealed to be characteristic of diphtheria agents. What investigation should be additionally performed to make a conclusion, that these microorganisms are pathogenic diphtheria bacilli?

Answer options

1. Determine urease activity
2. Determine amylolytic activity
3. Determine proteolytic properties
4. Determine toxigenic properties
5. Determine cystinase activity

Explanation

Diphtheria bacilli undergo phage conversion and become toxigenic. The action of toxins in the pathophysiology of the disease so determining toxigenic properties is a sure way to confirm the diagnosis of diphtheria.