Optochin discs and resp specimens

["Miller, J. Michael PhD ", Mike]

Recently, a question was asked on the net about using optochin disks on the 
initial inoculum of a sputum culture.
     Optochin disks are not placed on the initial inoculum of sputum 
cultures.  In fact, the test requires a pure culture inoculum and careful 
measuring of zone size to determine results.  After incubation in CO2, a 6-mm 
disk must produce a zone of 14-mm or more before calling the strain a 
pneumococcus.  A zone less than 14-mm is "questionable" for pneumococci and 
must be confirmed some other way.  If you use a 10-mm disk, the zone size for 
a pneumococcus must be at least 16-mm.  You can't do this test accurately on 
mixed culture streaks from direct specimens.