Microbiology Flashcards
(47 cards)
MTB vs NTM
MTB - Mycobacterium Tuberculosis (droplet transmission)
NTM - Non-Tuberculosis Mycobacteria (everywhere, e.g. water, soil)
Mycobacterium Microcrobiology
Non-motile rod shaped Gram +ve Intracellular Aerobic Thick, waxy cell wall Relatively slow growing (cf other bacteria)
Mycobacterium Staining
Acid alcohol fast bacilli (AAFBs) Sputum sample: 1. Auramine - fluorescence 2. Ziehl Neelsen (ZN) Stain - stay pink when decolouriser is added 3. Gram +ve
NTM
Environmental or atypical mycobacteria
No person-to-person transmission
A/w immunosupression
Resistant to classical anti-TB tx
“Slow growing” NTM - M. Avium Intracellulare (MAI)/ M. Avium Complex (MAC)
“Slow growing”
Pulmonary - immunocompetent w/ underlying lung disease e.g. bronchiectasis, cavities, CF, COPD (resembles TB)
Children - pharyngitis/cervical adenitis
Immunosupressed = disseminated infection - cytotoxics, lymphoma, HIV (multibacilllary infection, bacteraemia - longstanding diarrhoea)
“Slow growing” NTM - M. Marinum
“Slow growing”
Swimming/fish tank pool granuloma
Single/clusters of papules/plaques
Swimming pool/aquarium owners
“Slow growing” NTM - M. Ulcerans
Skin lesions e.g. Bainsdale, Buruli ulcer
Chronic progressive painless ulcer
Seldom fatal
Deformity
“Rapid growing” NTM
M. Abscessus, M. Chelonae, M. Fortuitum
Skin/ soft tissue infection
Hospital setting - isolated from blood culture vascular catheters, other devices
Usually treat with macrolide
Treatment of M. Avium Intracellulare (MAI)
Clarithromycin/azithromycin
Rifampicin
Ethambutol
+/- Amikacin/streptomycin
Features of Leprosy (M. Leprae and M. Lepromatosis)
Lifelong illness
Incubation period 2-10 years
Transmission nasal secretions (poor)
Manifestations of Leprosy (M. Leprae and M. Lepromatosis)
Nerves = thickening/ damage –> sensory neuropathy/hypothesia
Disability secondary to nerve damage
Skin = depigmentation/ plaques/ trophic ulcers etc
Profound disfigurement
Eyes (keratitis) and bone (periositis aseptic necrosis)
Tx of Leprosy (M. Leprae and M. Lepromatosis)
Rifampicin
Dapsone
Clofazime - if multibacillary
Immunological Spectrum of Leprosy
- Tuberculoid (TT) - paucibacillary
Few bacilli in skin lesions
Th1 mediated - robust response - Lepromatous (LL) - multibacillary
Abundant bacilli in multiple skin lesions, neuropathic ulcers
Th2 mediated - poor response
(Also in between - BT, BB, BL)
MTB Presentation
Cough Haemoptyisis Fever (night sweats) Weightloss Malaise
MTB Complex Microbiolgy
7 closely related species
M. bovis - infection via contact with cows (e..g unpasteurised milk)
M. africanum - West Africa
MTB Transmission
Droplet/ airborne
Infectious dose = 1-10 bacilli
Air remains infectious up to 30 mins
MTB Prevention
BCG vaccine Live attenuated strain M. Bovis Babies in high prevalence communities Efficacy 70-80% prevention of severe childhood TB Protection wanes Contraindicated in HIV
MTB Natural History
Primary TB
Latent TB
Reactivation (Post-primary)
Primary TB
Asymptomatic (usually) Ghon focus/ complex Granuloma Ipsilateral lymphadenopathy Rarely - erythema nodosum Occassionally - miliary/ diseminated
Post-Primary TB
Reactivation (exogenous re-infection)
>5 year post primary
Risk factors = immunosupression, chronic alcohol use, malnutrition, ageing
Pulmonary TB
Caeating granulomata - lung parenchyma, mediastinal LN
upper lobe
Extra-pulmonary
Lymphadenitis - scrofula, cervical LNs
GI
Peritoneal
Genitourinary - slow progression to renal disease, spread to lower urinary tractmmon)
Bone/joint - haematogenous spread (spine/Potts disease most common)
Spinal Tb
back pain
haematogenous spread
iliopsoas abscess
tx 12/12 anit-TB
TB Drugs (1st Line)
Rifampicin - drug interaction (raised transaminases, induces CYP450), orange secretions, hepatotoxicity Isoniazid - peripheral neuropathy, give B6/pyrodoxine Pyrazinamide - hyperuricaemia, hepatotoxicity Ethambutol - optic neuritis