Microbiology - Mycobacteriology
Reporting Procedure and Interpretation
Results are reported on computer-generated forms and returned to the submitting agency. The results are also available online at http://slph.ncpublichealth.com. The Laboratory does not retain hard copies of results, since computer records are copied to microfiche and therefore accessible when necessary. Duplicate reports for appropriate notification of results are the responsibility of the agency submitting the specimen. Refer to the NC TB Policy for reporting regulations.
Microscopic (Smear) Report
A smear of the concentrated clinical specimen is examined and reported within 24 hours of receipt and the laboratory. Smears are not performed on bloods or bone marrow speciments as they are not appropriate specimens for fluorescence smear and analysis. Reports may be as follows:
- Found -- indicates the presence of acid-fast organisms in the smear
- Per Field -- indicates the approximate number of acid-fast organisms seen per microscopic field
- Not Found -- indicates the absence of acid-fast organisms in the smear
Real-time PCR (PCR)
AFB smear positive sample - PCR will be performed on the first AFB smear positive sample for each patient.
- If the PCR result is positive on any AFB smear positive sample, PCR will not be performed on the subsequent samples. The sample will still be cultured and TB isolates tested for drug susceptibility as usual.
- If the PCR result is negative on any AFB smear positive sample, then testing for inhibitors will be performed.
AFB smear negative samples- PCR will only be performed on patients who are at an increased risk of tuberculosis and who demonstrate signs and symptoms consistent with pulmonary TB (see Appendix A Mycobacteriology in SCOPE).
- If the PCR test is negative on any AFB smear-negative sample, up to two more samples will be tested.
- If the PCR test is negative on all three AFB smear-negative samples, then the AFB culture is the final definitive result.
Culture Report
Cultures are incubated for a maximum of six weeks. If growth occurs, organisms are identified, if possible, by high pressure liquid chromatography or nucleic acid probes. Identification of some organisms may necessitate subculturing for biochemical tests or susceptibility testing which may require up to several additional six weeks.
A report of "no growth" indicates that no acid-fast organisms have grown by the end of six weeks. If growth resembling mycobacteria is observed, identification testing is performed as quickly as possible. If there is overgrowth of other bacteria, the specimen is reported "Contaminated". Reports of "no growth" require six weeks from receipt of the specimen.
Final identification reports (including susceptibility results, where appropriate) may require three to twelve weeks for all tests to be completed. If isolates are submitted to the CDC for further testing or confirmation, additional time will be required.
Drug Susceptibility Tests
Indirect drug susceptibility tests for M.tuberculosis complex are performed using five first-line drugs. Second-line drugs are tested when resistance is seen on first-line testing. Selected drug screenings are performed for clinically significant isolates of M.kanasaii and M.marinum.
High Pressure Liquid Chromatography (HPLC)
HPLC is currently our standard method of identification. This test is correlated with morphological data and other identification methods (DNA probes and/or biochemical testing) when necessary.
Relevant Links:
See also:
- About Microbiology
- Botulism
- Bordetella Pertussis
- Enteric Bacteriology
- Foodborne Illness
- Cholera
- Legionella
- Mycobacteriology
- Mycology
- Neisseria Gonorrhoeae
- Norovirus
- Parasitology
- Special & Atypical Bacteriology
