This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: RNTCP, Subject name: Social & Preventive Medicine
For sputum smear to come positive on ZN staining there should be minimum:- 
Select and explain. 
A. 100 bacilli per per ml sputum, B. 1000 bacilli per ml sputum, C. 2000 bacilli per ml sputum, D. 10,000 bacilli per ml sputum
D: 10,000 bacilli per ml sputum
Answer: D: 10,000 bacilli per ml sputum 
Explanation: Sputum smear microscopy for tubercle bacilli is positive when there are at least 10,000 organisms present per ml of sputum. ZN staining in RNTCP: Acid fast bacilli of TB; 'Rod shaped' with 'beaded appearance'. >10,000 bacilli per ml sputum must be present for a positive result.