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HelpTest Code MTBPZ Mycobacterium tuberculosis Complex, Pyrazinamide Resistance by pncA DNA Sequencing, Varies
Infectious
Reporting Name
Mtb PZA Resistance, pncA SequencingUseful For
Detection of genotypic resistance to pyrazinamide by Mycobacterium tuberculosis complex isolates
Reflex Tests
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| MTBVP | Mtb PZA Confirmation, pnc A Sequence | No, (Bill Only) | No |
Testing Algorithm
When this test is ordered, the reflex test may be performed and charged.
Method Name
DNA Sequencing
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
VariesShipping Instructions
1. See Infectious Specimen Shipping Guidelines.
2. Place specimen in a large infectious container (T146) and label as an etiologic agent/infectious substance.
Necessary Information
Specimen source and suspected organism identification are required.
Specimen Required
Specimen Type: Organism
Supplies: Infectious Container, Large (T146)
Container/Tube: Middlebrook 7H10 agar slant
Specimen Volume: Isolate
Collection Instructions: Organism must be in pure culture, actively growing.
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Varies | Ambient (preferred) | ||
| Refrigerated | |||
Reject Due To
| Agar plate | Reject |
Special Instructions
Reference Values
Pyrazinamide resistance not detected
Day(s) Performed
Varies
CPT Code Information
87153-Mtb PZA Confirmation, pncA Sequence
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| MTBPZ | Mtb PZA Resistance, pncA Sequencing | 46245-7 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| MTBPZ | Mtb PZA Resistance, pncA Sequencing | 46245-7 |
Clinical Information
The protein product of the Mycobacterium tuberculosis complex pncA gene is an enzyme that is responsible for activation of the prodrug pyrazinamide (PZA). DNA sequencing of the Mycobacterium tuberculosis complex pncA gene can be used to detect mutations that correlate with in vitro PZA resistance.(1,2) The sequencing result can be available in as little as 1 day after the Mycobacterium tuberculosis complex isolate grows in culture, thereby providing a more rapid susceptibility result than the average 10 to 14 days required by phenotypic broth methods.
Interpretation
Polymorphisms in the pncA gene that have been previously correlated in our laboratory with pyrazinamide (PZA) resistance will be reported as "Mutation was detected in pncA suggesting resistance to pyrazinamide."
Wildtype pncA or a silent pncA gene polymorphism (ie, no change in the amino acid translation) will be reported as "No mutation was detected in pncA."
New polymorphisms in the pncA gene that have not previously been seen in our laboratory will require additional testing using a reference broth method to determine their correlation with PZA resistance.
Cautions
According to the literature,(3) 72% to 97% of pyrazinamide (PZA)-resistant clinical isolates carry mutations in the pncA gene or promoter region. However, other resistance mechanisms (eg, changes in PZA uptake or increased PZA efflux) will not be detected by this method.
Correlation of the in vitro sequencing result with clinical presentation is strongly recommended.
Method Description
Organisms identified as Mycobacterium tuberculosis complex using the Mycobacterium tuberculosis AccuProbe (GenProbe) are lysed using the PrepMan Ultra lysis buffer. Using the pncA primers described by Shenai and colleagues, an approximately 700 base pair-polymerase chain reaction (PCR) product is generated that flanks the entire pncA gene and the upstream promoter region. The PCR product is cleaned and sequenced using the Big Dye terminator v 1.1 Cycle Sequencing reagents (Applied Biosystems). Results are analyzed versus the wildtype pncA sequence using MicroSeq Microbial ID software. A custom library of non-wildtype sequences was constructed in MicroSeq. An exact match to the custom nucleotide library is required to report the result.(Shenai S, Rodrigues C, Sadani M, Sukhadia N, Mehta A: Comparison of phenotypic and genotypic methods for pyrazinamide susceptibility testing. Indian J Tuberc. 2009;56(2):82-90)