Mycobacterium tuberculosis Flashcards

Question

Culture

Answer 1

Gold standard for laboratory confirmation of TB Culture media include Egg based (Lowenstein-Jensen, Petragnani, American Thoracic Society medium) Agar based (Middlebrook 7H10 or 7H11) Liquid based (Middlebrook 7H9, 7H12, etc) Growth is faster in liquid media and allows detection in 1-3 weeks BSL 3

Answer 2

initial decontamination remove fast-growing non-mycobacterial organisms Liquefaction to allow access of decontaminants to nonmycobacterial organisms and media nutrients to surviving mycobacteria. N-acetyl-L-cysteine in 1% sodium hydroxide solution Centrifugation for concentration Neutralization by buffer

Answer 3

Recently developed automated liquid culture systems are faster and more sensitive. E.g. BACTEC 460TB BACTEC c-MGIT (Mycobacteria Growth Indicator Tube) 960 Versa TREK Myco BacT/Alert 3D ESP Culture Sytstem II

Answer 4

These have the advantages of being rapid and highly sensitive 1) In Situ Hybridization Uses an oligonucleotide probe labeled with a detector molecule If the detector molecule is fluorescein, and interpretation is by fluorescence microscopy, this is referred to as Fluorescence In Situ Hybridization (FISH) If detection is by secondary reaction and color change, it is termed Chromogenic In Situ Hybridization (CISH) Used to identify M.tuberculosis in cultures and direct respiratory specimens 2) Nucleic acid amplification (NAA) Enhanced Amplified-MTD (Amplified Mycobacterium Tuberculosis Direct) test:- detects M.tuberculosis mRNA *from both smear positive and smear negative specimens Ampiclor MTB test:- detects M.tuberculosis DNA *smear positive specimens only Interpretation of NAA should be correlated with AFB smear results Positive NAA + positive smear :- strongly indicates TB Positive NAA + negative smear:- initiate treatment based on clinical assessment while awaiting culture results NAA detect nucleic acids from both living and dead organisms May remain positive during and after therapy. Hence, should not be used to assess infectivity or response to treatment 3) Xpert MTB/RIF A catridge-based automated diagnostic test which identifies M. tuberculosis and resistance to rifampicin Was endorsed in Dec. ‘10 by WHO for use in TB endemic countries How it works It purifies and concentrates MTB bacilli from sputum sample Isolates genomic material from captured bacilli Amplifies genomic DNA by PCR Identifies all relevant Rifampicin resistance inducing mutations in the RNA polymerase beta (rpoB) gene

Answer 5

Advantages of Xpert MTB/RIF Results from unprocessed sputum are obtained within 90 mins Minimal training required Minimal biohazard Disadvantage Expensive

Answer 6

Gene expert

Answer 7

Culture using Zeihl Neelson stain

Answer 8

1. Xpert MTB/RIF A catridge-based automated diagnostic test which identifies M. tuberculosis and resistance to rifampicin Was endorsed in Dec. ‘10 by WHO for use in TB endemic countries How it works It purifies and concentrates MTB bacilli from sputum sample Isolates genomic material from captured bacilli Amplifies genomic DNA by PCR Identifies all relevant Rifampicin resistance inducing mutations in the RNA polymerase beta (rpoB) gene 2. TB-LAMP------------loop mediated isothermal amplification (TB Complex 3. Truenat (detect Rif resistance [rpoB]) 4. Line probe assay (LPA) Detect Rif resistance and 2nd line medications

Answer 9

1. First-line drugs (Via DOTS): Isoniazid Rifampicin Ethambutol Pyrazinamide 2.Second-line drugs (ELIXIR post MDR-TB mgt) * aminoglycosides: e.g., amikacin, kanamycin * polypeptides: capreomycin, viomycin, enviomycin * Fluoroquinolones: e.g., Gatifloxacin, moxifloxacin * thioamides: e.g. ethionamide, prothionamide * Cycloserine * Terizidone 3. Third-Line drugs * Rifambutin * Macrolides: eg. clarithromycin * Linezolid *Thioacetazone * Thioridazine;

Answer 10

Primary resistance: occurs in persons who do not have a history of previous treatment and these individuals are initially infected with resistant organisms. Secondary resistance: occurs during therapy for TB, either because the patient was treated with an inadequate regimen or because the patient did not take the prescribed regimen appropriately (non adherence). Mono-drug resistance: Resistant to one drug (mono isoniazid or monorifampicin) Poly-drug resistance: Resitant to greater than 2 drugs apart fromm isoniazid and rifampicin Obsolete terms: Multidrug resistant TB (MDR-TB) – resistant to at least Isoniazid and Rifampicin Extensively drug resistant TB (XDR-TB) – resistant to at least Isoniazid and Rifampicin, a Quinolone, and one of the 2nd line injectables (amikacin, kanamycin, capreomycin) Others: As of January 2021, WHO introduced new definitions for pre-XDR-TB and XDR TB MDR-TB (remained unchanged): Resistance of M. tuberculosis strains to at least isoniazid and rifampicin (called rifampin in the US), the cornerstone medicines for the treatment of TB Rifampicin-resistant disease (RR-TB) on its own requires similar clinical management as MDR-TB Poly-drug resistant TB indicates resistance to two or more anti-TB drugs but not to both Isoniazid (INH) and Rifampicin (R) simultaneously Pre-XDR-TB is now defined as TB caused by M. tuberculosis strains that are resistant to isoniazid, rifampicin, and any fluoroquinolone (+ second line injectables) XDR-TB is now defined as TB caused by M. tuberculosis strains that are resistant to isoniazid, rifampicin, any fluoroquinolone, (+ second line injectables) and either bedaquiline or linezolid (or both).

Answer 11

Treatment is with Pretomanid, bedaquiline and linezolid (Nix-TB) +/- newer quinolones

Answer 12

Nix-TB was a prospective study of a regimen of bedaquiline (400 mg daily for two weeks followed by 200 mg 3 times a week), pretomanid (200 mg per day) and linezolid (1 200 mg per day) for six months Myelosuppression and peripheral neuropathy ZeNix trial Patients were treated for six months with bedaquiline 200 mg daily for eight weeks followed by 100 mg daily for 18 weeks), pretomanid (200 mg daily) and were equally randomized, dose-blinded, to daily linezolid starting at 1200 mg for six months (1200L6M), 1200 mg for two months (1200L2M), 600 mg for six months (600L6M), or 600 mg for two months (600L2M)

Answer 13

BCG Vaccine Bacillus Calmette-Guérin (BCG) 1924

Answer 14

15th December, 2022, WHO reintroduces another change in the treatment of drug resistant TB 6 months course of oral bedaquiline, pretonamid, linezolid and Moxifloxacin Shortens duration and more effective

Mycobacterium tuberculosis Flashcards

(40 cards)