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No. 4, 2009

MYCOBACTERIOLOGY LABORATORY BRANCH UPDATE

MLB Offers New Drug Testing Service

The Mycobacteriology Laboratory Branch (MLB) of DTBE has implemented a new testing service for the rapid molecular detection of drug resistance (MDDR) in isolates of multidrug-resistant M. tuberculosis complex (MDR TB).  This service will use DNA sequencing to identify the mutations most frequently associated with resistance to rifampin (RIF) and isoniazid (INH).  In addition, MLB will examine genetic loci associated with resistance to the most effective second-line drugs, fluoroquinolones (FQ) and the injectables amikacin (AMK), kanamycin (KAN), and capreomycin (CAP). Although the presence of a mutation indicates that a clinical isolate is most likely resistant to the drug of interest, the absence of a mutation is not confirmation of drug susceptibility. Therefore, all isolates will also undergo conventional drug-susceptibility testing using agar proportion to determine phenotypic resistance to first- and second-line drugs (RIF, INH, ethambutol, streptomycin, ofloxacin, ciprofloxacin, KAN, CAP, AMK, ethionamide, and para-aminosalicylic acid). PZA testing will be performed by the MGIT 960 method. Molecular and conventional results will be analyzed and released in a final report.

TB cases must meet one of the following criteria for isolates to be accepted for MDDR testing:

  • High risk for RIF resistance or MDR TB (e.g., previous TB; MDR TB contact; foreign-born)
  • Known RIF resistance
  • Patient works in high-risk setting (e.g., daycare worker, nurse)
  • Patient adverse reaction (e.g., RIF allergy)
  • Mixed or nonviable culture

Other isolates may be accepted on a case-by-case basis. All isolates must be submitted on either solid media or as MGIT cultures. BACTEC 460 vials will not be accepted.

The MDDR service offered by MLB will improve TB elimination efforts in the United States by quickly identifying MDR TB, which is critical for the appropriate treatment of patients and efforts of TB programs to control the spread of TB.

—Submitted by Mitchell A. Yakrus, MS, MPH
Mycobacteriology Laboratory Branch

Laboratory Services for Nontuberculous Mycobacteria Transferred to Clinical and Environmental Microbiology Branch

Historically, the Mycobacteriology Laboratory Branch (MLB) in DTBE has provided reference services for the identification and typing of nontuberculous mycobacteria (NTM) and for laboratory support in investigations of outbreaks due to NTM. While species identified as NTM can cause pulmonary disease, sources of infection are environmental, and person-to-person transmission has not been documented. Since control programs for TB are not appropriate for NTM, these services and support for NTM will no longer be offered by MLB. They will instead be provided by the Clinical and Environmental Microbiology Branch (CEMB) of the Division of Healthcare Quality Promotion (DHQP). In the past, MLB has worked closely with CEMB by providing laboratory support for epidemiological investigations involving NTM in healthcare settings.

The laboratory services offered by CEMB will be quite similar to those provided by MLB.  For submission of isolates, laboratories must provide data to demonstrate that the isolate is not Mycobacterium tuberculosis and that the isolate is clinically significant. CEMB will continue to use a combination of high performance liquid chromatography (HPLC) and 16s rRNA gene sequence analysis for identification of NTM. Pulsed-field gel electrophoresis (PFGE) will be used to type isolates in support of outbreak investigations. MLB will retain all isolates and laboratory reports for NTM previously submitted to CDC.

Institutions have been officially notified of the specific services to be provided along with requirements for submission of isolates, through announcements from the Association of Public Health Laboratories (APHL) and CEMB. For further information, please contact Brandi Limbago in CEMB at 404-639-2162.

—Submitted by Mitchell A. Yakrus, MS, MPH
Mycobacteriology Laboratory Branch

 

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