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Interpretation of FL-LPA: Predicting Drug-resistance in Special Cases
Learning Objectives- Understand the nuances and challenges associated with interpreting First Line - Line Probe Assay (FL-LPA) results for predicting drug resistance in special cases.
- Learn about some specific scenarios/special cases.
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Predicting Drug Resistance in Special Cases
- When specimen tested contains a hetero resistant strain:
- Mutated as well as a wild-type sequence can be detected
- One of the mutation probes as well as corresponding wild type probe may stain positive on the respective strip
- Whether the respective resistance becomes phenotypically evident, depends on the ratio of mutated and nonmutated sequences
- The tested specimen contains more than one M. tuberculosis complex strain (due to mixed culture or contamination):
- One of these strains harbors a mutation, one of the mutation probes as well as the corresponding wild type probe may stain positive.
- Whether the respective resistance becomes phenotypically evident, depends on the ratio of the resistant and sensitive strain
- Due to mixed infection with M. tuberculosis complex strain and a nontuberculous mycobacterium:
- The TUB band may be missing
- If resistance pattern develops, presence of M. Tuberculosis complex must be suspected and repeat test
- All bands of a gene locus (including the Locus Control band) missing completely on a test strip:
- DNA concentration below the limit of detection or indicates the presence of interfering substances
- Repeat test
- If cultivated sample generates result with complete katG locus missing
- Indicates Isoniazid resistance
Resources
- GenoType MTBDR plus ver 2.0 kit, Instructions for Use.
- GLI Line Probe Assays for Drug-resistant Tuberculosis Detection.
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