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MLT-Mycobacterium

Microbiology

QuestionAnswer
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
Created by: kencho