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Using a proprietary antibiotic- impregnated strip method, Stanford has validated the performance of in-house susceptibility testing for rapidly growing mycobacteria. |
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Mycobacteriology
Microscopy:
Direct microscopic exam with fluorescent stain is performed routinely. A STAT (approximately 2 hour turnaround time) AFB stain is available for initial sputum from patients with suspected untreated tuberculosis, however this process renders the specimen unsuitable for other studies and additional samples must be submitted for culture.
Direct detection of Mycobacterium tuberculosis using real-time PCR:
Real-time PCR for detection of M. tuberculosis complex is automatically performed on smear-positive respiratory specimens. Smear-negative specimens are tested by request. Genotypic susceptibility testing for rifampin and isoniazid are performed by request at California Department of Public Health Laboratory.
Culture and identification of mycobacteria using broth and plates:
Microbiology uses Middlebrook plates and a special automated broth incubation system for detection of mycobacterial cultures. Positive isolates are identified with multiplexed, real-time PCR and ribosomal RNA gene sequencing. Mycobacterium tuberculosis complex and Mycobacterium chelonae-abscessus group are identified to species level. Aerobic actinomycetes, and Nocardia spp. in particular, are identified by ribosomal RNA gene sequencing.
Antibiotic susceptibility testing:
Mycobacterium tuberculosis complex isolates are tested for sensitivity to first-line drugs with the MGIT instrument. Second-line testing is performed at reference laboratories. Rapidly growing mycobacteria and other aerobic actinomycetes are tested with antibiotic-impregnated strip method.
