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AFB CULTURE, MYCOBACTERIAL CULTURE (clinical specimens)

Synonym(s):

​Culture for Mycobacterium Species, TB Culture

Lab Section Category

Description

Indications

Specimen Required

​Sputum, bronchoalveolar lavage, CSF, body fluids, gastric lavage, tissue, urine, pus, etc

Storage and Transport

Method

​Culture by MGIT non-radiometric method and LJ solid media. Alternate media include 7H10/11 solid media.

Includes reflex testing as follows:
1. TB susceptibility testing
First-line susceptibility testing for M. tuberculosis (MGIT method) for the first MTBC isolate cultured from new TB cases and upon follow-up at 6-8 weeks. Second-line panel (ofloxacin, kanamycin, ethionamide) testing is automatically performed for isolates resistant to isoniazid, rifampin or ethambutol; and extended-line testing (capreomycin, clofazimine, PAS) for XDR isolates (resistant to isoniazid, rifampin, ofloxacin and kanamycin). If MTBC is isolated in tissue from infants <2 years old, subspeciation of M. bovis subsp BCG will be performed instead of drug susceptibility testing.

2. Identification of NTM from clinically significant sites like blood, bone marrow, BAL, bronchial wash, CSF, skin and tissue. For sputum isolates, this involves identification of every 2nd NTM out of 3 and every 3rd NTM if isolated after 3 months from the second; and if isolated from smear-positive specimens.

Special requests and charges apply for the following:
- M. tuberculosis isolates that do not meet the above criteria for reflex susceptibility testing
- Pyrazinamide susceptibility testing of M. tuberculosis
- Extended-line susceptibility testing for M. tuberculosis e.g. Capreomycin, clofazimine and PAS
- Identification of NTM isolated from sputa that do not meet the above criteria for reflex testing
- Subspeciation of M.tuberculosis complex** e.g. BCG, M. bovis etc

Test Results

​- M. tuberculosis complex**isolated.
- Susceptibility test result pending / refer to previous cultures for susceptibility test results. 
- Presumptive nontuberculous mycobacteria isolated***
- AFB culture overgrown with non-mycobacterial organism/s.
- No growth of AFB

Reference Interval / Value

Turnaround Time

Receipt of specimen to detection of growth (average: 21 days). Affected by type of organism, specimen received and prior antibiotic treatment.

Detection of growth to final identification (range of 2 days to 4 weeks, average 5-7 days for MTBC). Affected by slow growing mycobacteria, mixed cultures requiring additional processing and repeat cultures.

Negatives: 8 weeks; 6 weeks for Myco-F lytic samples 

Day(s) Test Set up

​Monday - Saturday

Remarks

** M. tuberculosis complex includes M. tuberculosis, M. bovis, M. bovis BCG, M. africanum, M. canettii and M. microti. 


*** Less than 1% of acid-fast bacteria isolated may include weakly acid-fast aerobic actinomycetes like Nocardia, Rhodococcus, Gordonia and Tsukemurella species.

Change History Notes

  • 16 Oct 2015 06:10 PM

    Remove "BACTEC 460 Radiometric" as alternate media

  • 18 Sep 2017 02:45 PM

    Amend spelling for Clofazimine

  • 15 Jan 2018 06:35 PM

    Added in "If MTBC is isolated in tissue from infants <2 years old, subspeciation of M. bovis subsp BCG will be performed instead of drug susceptibility testing." under TB ST.

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