When using a rapid (3 hour) automated antimicrobial susceptibility test system, is it necessary to perform a purity check plate on the test inoculum suspension?  Some of our technologists do not feel this is useful because the MIC results are reported BEFORE the purity plates are examined. 

Answer:

Yes.  Purity check plates are still useful even if the plates are examined 10-15 hours after the MIC results are reported.  It is important to verify that the MIC results were generated from a pure culture.   Despite the fact that the plates are examined after the report is issued, they still represent an important quality assurance tool.  An amended report may be necessary if the antimicrobial susceptibility profile for an organism does not match with the organism's identification. Atypical results must be verified before being released, which would include examination of the purity check plate.  Suggestions for this procedure are described in NCCLS M39-A.