This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
In a completely and adequately immunized child against Diphtheria, the throat swab was collected. It showed the presence ofCorynaebacterium diphtheriae like organisms on Albe staining. These orgainisms can have one of the following propeies on fuher laboratory processing - 
Select and explain. 
A. It can grow on Potassium tellurite medium, B. It would show a positive Elek's gel precipitation test, C. It can be pathogenic to experimental guinea pigs, D. It can produce cytotoxicity in tissue cultures
A: It can grow on Potassium tellurite medium
Answer: A: It can grow on Potassium tellurite medium 
Explanation: Ans. is 'a' i.e., It can grow on Potassium tellurite medium This child is a carrier of Diptheria. Remember, adequate immunization does not prevent the carrier state because the vaccine is active against the toxin (not against the organism). Tellurite medium is paicularly impoant in the isolation of diptheria bacilli from convalescent, contacts and carriers as in these cases they may be out numbered by the other bacteria. The other three options are about the virulence testing of the isolated bacilli. (see above explanation) These tests will be positive only if the isolated diphtheria like organism is virulent. Otherwise all of them will be negative.