Evaluation of First-line Line Probe Assay Strip

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.

Resources

• GenoType MTBDR plus ver 2.0 kit, Instructions for Use.

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