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Each strip for First Line – Line Probe Assay (FL - LPA) has a total of 27 reaction zones (Figure below).

 

The Key Zones Include:

 

Conjugate Control (CC)

  • Indicates the efficiency of conjugate binding and substrate reaction

 

Amplification Control (AC)

  • Develops when control amplicon binds indication correct procedure was followed
  • The absence of AC zone indicates an invalid test

M. tuberculosis Complex (TUB)

  • Hybridizes with amplicons generated from Mycobacterium tuberculosis complex
  • The absence of TUB zone indicates the absence of M. tuberculosis complex
     

Locus Controls (rpoB, katG, and inhA)

  • Detect gene region specific for genes rpoB/ katg/ inhA
     

Wild-type Probes

  • Comprise the resistance regions of respective genes (rpoB/ katg/ inhA)
  • The absence of signal for at least one of the wild type probes indicates the resistance of the tested strain to the respective antibiotic

 

Mutation Probes

  • Detect most common resistance-mediating mutations (rpoB/ katg/ inhA)
  • Each pattern deviating from the wild-type pattern indicates resistance

 

Figure: Key Zones of FL - LPA Evaluation Strip; Source: GenoType MTBDR plus ver 2.0 kit, Instructions for Use.

 

 

Evaluation of Assay Strip for FL - LPA Zones:

  • The resistance status is determined and noted for each respective column.
  • Distances between single probes on the strips may vary slightly.
  • Not all bands of a strip have the same signal strength.
  • The DNA strip should only be interpreted when:​
    • AC, CC and TUB bands are present​
    • Along with the presence of locus control bands for rpoB, katG and inhA
    • Only those bands whose intensities are about as strong as, or stronger than that of the AC zone are to be considered.​
  • Bands whose intensities are about as strong as or stronger than that of the AC zone are considered.

 

Important: For an accurate evaluation, align provided template separately for each locus with the respective Locus Control band.

 

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