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
Investigation of choice of diphtheria carrier is:- 
Select and explain. 
A. Throat Swab Culture, B. Gram's stain, C. Albe stain, D. Zeihl Neelsen stain
A: Throat Swab Culture
Answer: A: Throat Swab Culture 
Explanation: Investigation of choice of diphtheria carrier is throat swab. Carriers are detected by cultural methods - swabs are taken from nose and throat and it is examined by culture methods for diphtheria bacilli. Source of infection: Carriers (95%) are more common source of infection than cases (5%). Types of Carriers: Temporary (persists for a month) Chronic (persists for a year) Nasal carriers are more dangerous due to frequent shedding than throat carriers. Option 2, 3: Gram Stain and Albe stain aids in identification of C. diphtheriae but not the Investigation of choice of diphtheria carrier. Option 4: Zeihl Neelsen stain: for Mycobacterium species.