Can cording seen on AFB staining from the bottle be used as a direct confirmatory test for identification of MTB?
Dear Gulnaz,
The cords seen on AFB strongly suggest MTB, being highly specific if the observed has experience. However, other species can show sometimes this pattern, such are M. kansasii and M. fortuitum. On the other hand, MT not always shows cords. The most rapid confirmatory method probably is the detection of MPT 64 Ag, commercially available and very easy to perform.
I would suggest using MPT64 test. All you do is aliquot 100 ul onto a test strip. If contamination is a concern, you swab 100 ul onto blood agar or tryptic soy agar and incubate for 24 hours. If any growth is seen, then it suggests contamination.
MPT 64 ag test is the option. We are even playing with the idea of rapid DST confirmation of broth cultures using MPT64. see Ochang et al 2013 APJTD for our published initial data.
We have started using MPT64 for direct identification of MTB complex from positive BacTAlert bottles. Previously we relied on PCR and conventional biochemical tests for the same. But this test gives accurate results within 15 minutes.
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