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MLT-Mycobacterium
Microbiology
| Question | Answer |
|---|---|
| What is the basic info about Mycobacterium? | 1.Gram positive rod 2.Non motile 3.Non spore forming 4.Strict aerobe |
| What are the example species of Mycobacterium? | 1.M.tuberculosis -> Human tuberculosis 2.M.leprae -> Human leprosy |
| Whats the characteristics of Mycobacterium cell wall? | 1.Thick and waxy: Mycolic acid, highly hydrophobic 2.Impermitable to stain and antibiotics 3. No outer membrane -> Gram positive 4.Acid-fast |
| What are the slow grower of Mycobacterium? | 1.Requires >7 days to produce colony 2.M. tuberculosis complex and M. avium complex requires 6-8weeks |
| What are the fast grower of Mycobacterium? | 1.Produce colonies in less than 7 days 2.M. fortuitum, M. chelonae |
| What is Photochromogens? | With light, the colony will be pigmented as yellow. Eg.M.marinum |
| What is Scotochromogens? | The colony will be pigmented as yellow, with or without light. Eg.M. gordonae |
| What is Non-photochromogens? | Only non-pigmented colonies. Eg.M. tuberculosis complex, M. avium complex |
| What is the mechanism of Pulmonary tuberculosis? | 1.Mycobacterium reaches alveoli. 2.Macrophage engulf 3.Waxy cell provide protection 4.Macrophages secret more cytokines and fibroblast 5.These cells fuse together and form GRANULOMA |
| What is latent TB? | Mycobacteria survive inside granuloma without causing disease |
| What is Active TB? | When immune systems weakened, mycobacteria break through the granuloma and cause necrosis |
| What is extra-pulmonary tuberculosis? | 1.In 10% of active TB, M.tuberculosis disseminate all over the body via blood and lymphatic system 2.also called Military TB |
| What are the specimen for the diagnosis? | 1.Pulmonary: Sputum, Bronchoalveolar lavage 2.Extrepulomany: Blood, urine, tissue biopsy, body fluid or feaces |
| The pros and cons of AFB smear staining? | Pros: 1.direct perform on sputum smear 2.the most rapid Cons: 1.low sensitivity, only about 60% detection rate 2.Cannot differentiate M. tuberculosis from other mycobacteria |
| What are the types of acid fast stain? | 1.Ziehl-Neelsen stain 2.Auramine O fluorescent stain |
| What is Auramine O Fluorescent stain? | 1.Yellow fluorescent stain 2.Auramine O as principle dye 3.0.5% acid alcohol as decolourization agent 4.potassium permanganate as a counterstain 5.Positive: Yellow |
| What is Ziehl-Neelsen stain? | 1.Classical stain 2.1% carbol fuchsin as principle dye 3.3% acid alcohol as decolorization agent 4.methylene blue as counterstain 5.Positive: Red |
| What are the culture media for the TB? | 1. Lowenstein Jensen Medium(LJ) 2. Middlebrook 7H10 agar 3. Middlebrook 7H9 medium, liquid 4. Bactec MGIT 960, liquid |
| What is the LJ medium? | 1. Classical medium 2. Egg based 3. No antibiotic 4. Malachite green(anti fungal) |
| What is Middlebrook 7H10 agar? | 1. Contain oleic acid, albumin, dextrose and catalase 2. can add antibiotics to prevent from unwanted bacteria and fungi |
| What is Middlebrook 7H9 medium? | 1. Liquid medium 2. More efficient in cultivation of mycobacteria 3. easy to generate aerosol, so seldom used in clinical lab |
| What is Bactec MGIT 960? | 1. Liquid-based automated system 2. Detect the growth of bacteria based on depletion of O2 |
| What is the pre-culture treatment for TB? | 1. All respiratory specimens 2. Digested the specimens with N-acetyl-L-cysteine (NALC) or sputasol 3. Decontaminate with 1-2% NaOH to remove unwanted bacteria for 30mins, then weak acid |
| Mycobacteria withstand _____ pH whereas bacteria of respiratory tract were killed off? | High |
| What is culture condition for TB? | 1. Incubate at 37C for 6-8 weeks, examine weekly 2. Slow grower: colonies form in 4-6 weeks 3. Fast grower: colonies form in 1 week 4. LJ media incubate in O2 incubator 5. 7H10 agar require 5% CO2 enrichment |
| Whats the colony characteristics of TB? | 1. rough and buff-colored 2. roughness |
| Identification of M.tuberculosis nowadays relies on ? | Molecular tests on extracted DNA or direct specimens |
| What is Cobas TaqMan MTB test (Roche)? | 1. Real time PCR based 2. Target: 16S rDNA |
| What is Abbott RealTime M2000 (Abbott)? | 1. Real time PCR based 2. Target: S6110 |
| What does MIC mean in Antimicrobial Susceptibility testing? | Minimal Inhibitory Concentration |
| What are the tests for Antimicrobial Susceptibility testing? | 1. Agar proportion method: Middlebrook 7H10, gold standard, used by HA 2. Resistance ratio method: LJ medium, by comparing the MIC, used in DH |
| How to interpret the Agar proportion method results? | 1.Incubate at 37℃ for 6-8 weeks in presence of CO2 first. 2.If growth in partition 3 and 4 is similar or even exceed the growth in partition 2 -> Resistance |
| How to interpret the Resistance ratio method results? | 1.Incubate at 37℃ for 6-8 weeks first 2.MIC: <4: Sensitive 4-8:Suggestive of resistance >8: Resistant |