<prompt> For sputum smear to come positive on ZN staining there should be minimum:-100 bacilli per per ml sputum1000 bacilli per ml sputum2000 bacilli per ml sputum10,000 bacilli per ml sputum  <response>: 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. 