Microbiology Flashcards
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
TB Treatement
Isoniazid + Rifampicin + Pyrazinamide + Ethambutol = 2/12
Continue Isoniazid + Rifampicin for 4/12
(TB Meningitis - continue Isoniazid + Rifampicin for 8-10/12)
S. pneumonia features
Gram +ve diplococci rust sputum Lobar on CXR (vaccine for at risk groups) Alpha haemolytic - aerobic conditions Beta haemolytic - anaerobic conditions
H. influenza
Gram -ve cocco-bacilli
smoking/COPD (pre-existing lung disease)
chocolate agar
May produce Beta lactamase
M. catarrhalis
Gram -ve coccus
Smoking
aerobic
oxidase-positive diplococcus
S. aureus
Gram +ve cocci
“grape-bunch clusters”
pot-influenza infection
cavitation on CXR
K. pneumonia
Gram -ve, enterobacter
Haemoptysis
Alcohol
Elderly
Legionella pneumophilia
travel/air conditioning/water towers Hepatitis Low Na Can cause multi organ failure Buffered charcoal yeast extract (special culture)
Resp Infection in HIV
P. Jiroveci (PCP)
TB
Cryptococcus neoformans
Resp Infection in Neutropenia
Fungi - Aspergillus spp.
Resp Infection in Bone Marrow Tx
Aspergillus
CMV
Resp Infection in Splenectomy
Encapsulated Organisms - H. influenza, S. pneumonia, N. meningitidis
Resp Infection in CF
Pseudamonas aeruginosa
Burkholderia cepacia
Coxiella burnettii
Q fever
worldwide
domestic/farm animals - transmitted yb aerosol or milk
hepatitis
Empyema
Consider if not improving on Abx treatment
Difficult to treat - difficult to penetrate + acidotic environment
CAP Organisms
Typical (85%)
- S. Pneumoniae
- H. Influenza
Atypical (15%)
- Legionella
- Mycoplasma
- Coxiella burnetii
- Chlamydia psittaci
HAP Organisms
Staph Aureus Enterobacteriaciae - E. Coli, Klebsiella Pseudamonas spp. H. Influenzae Acinetobacter baumanii Fungi (Candida)
Pneumocystis jiroveci (PCP)
Protozoan Ubiquitous in environment Insidious onset Dry cough, weightloss, SOB, malaise CXR: 'bats wing' (bilateral ground glass shadowing) Dx immunoflouresence on BAK Rx septrin (co-trimoxalose) Immunosupressed - prophylactic septrin Walk test - desaturate will walking - definitive indication for PCP
Aspergillus fumigatus - resp infection
Allergic bronchopulmonary aspergillosis = chronic wheeze, eosinophilia, bronchiectasis
Aspergilloma - fungal ball in pre exosting cavity - haemoptysis
Invasive aspergillosis in prolonged neutropenia (immunocompromised) - treat with Amphotericin B
Diagnosis for Resp Tract Infection
Urine Antigen Test - not definitive. Severe CAP - S. Pneumoniae, Legionella
Ab Test -paired serum sample (presentation + 10-14/7). Rise in Ab level - Chlamydia, Legionella (difficult to culture)
Immunofluorescence - virology - PCP detected by silver stain
Neisseria Gonorrhoeae
obligate intracellular
Gram -ve diplococcus
Gonorrhoea
Opathalmia neonatorum = neontal conjunctivitis - transfer from birth canal to baby
Complement deficiency = disseminated disease
Complicated infection = PID - female infertility
Gonorrhoea Dx and Tx
Urethral (or rectal) smear and culture
Single dose ceftriaxone IM - 250mg
Single dose cefixime PO - 400mg
Resistant - spectinomycin IM - 2g
Chlamydia trachomatis
obligate intracellular
Gram -ve
cannot be cultured on agar
