This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic Bacteriology (Gram Positive Bacilli, Gram Negative Bacilli), Subject name: Microbiology
Elek's gel precipitation test is done for: 
Select and explain. 
A. Corynebacterium diphtheria, B. Salmonella choleraesuis, C. Clostridium botulinum, D. Diphtheroids
A: Corynebacterium diphtheria
Answer: A: Corynebacterium diphtheria 
Explanation: Elek's gel precipitation test is done for Corynebacterium diphtheriae. Detection of C. diphtheriae: Elek's gel precipitation test - Double diffusion in two dimensions (Ouchterlony procedure), Detection of tox gene by PCR. Detection of diphtheria toxin by ELISA or immunochromatographic test (ICT). Cytotoxicity produced on cell lines.