Mycobacteria Flashcards
- slender, slightly curved or straight rods
- non-motile, non-spore-forming
- cell wall has high lipid content (mycolic acid)
- acid-fast (resist gram stain)
- aerobic
- require complex media
- slow growers (2-6 weeks)
Mycobacteria
Mycobacteria media
complex media that supresses normal flora and pathogens
Two major Mycobacteria groups
- M. tuberculosis complex
- Nontuberculous mycobacteria (NTMs) or MOTT (Mycobacteria other than tubercle bacillus)
Mycobacterium tuberculosis Complex
- US pathogens: M. tuberculosis, M. bovis
- Other: M. africanum, M. canettii, M. microti, M. leprae
Primary tuberculosis
- transmitted by airborne droplet
- infect deep lung (alveoli)
- bacteria phagocytosed and multiply intracellularly
- T cells sensitize after 4-6 weeks
- Regression and healing of primary lesion
- Positive tuberculin skin test
- Kids: nonproductive cough
- Adults: small % develop progressive pulmonary disease
- reactivation can occur
Reactivation TB
- alteration or suppression of cellular immune system
- fever, shortness of breath, night sweats, chills, fatigue, etc.
- 20% asymptomatic
- eventually productive cough, chest pain
M. tuberculosis Complex (clinical diseases)
- Primary tuberculosis
- Reactivation TB
- Chronic disease
- Extrapulmonary TB
Chronic M. tuberculosis complex disease
- fibrosis
- calcifications
- complications (empyema, pleural fibrosis, etc.)
Extrapulmonary TB
- miliary TB (lungs to bloodstream to other organs)
- mostly in kids and HIV patients
- Pleural (cough, fever, chest pain)
- Lymphadenitis
- Gastrointestinal
- Skeletal TB of the spine (Pott’s disease)
- Meningeal (meningitis)
- Peritoneal
- Genitourinary TB
- slow growing
- raised, dry, rough colonies
- nonpigmented
- cord factor
- grow best at 35-37C
- positive niacin accumulation
- reduces nitrate
- nucleic acid probe available
M. tuberculosis
Cord factor
- toxic to our cells
- inhibits PMN migration
TB treatment
- 9 month course of therapy
- isoniazid and rifampin
- maybe streptomycin or ethambutol
- drug combo if resistant
Mutlidrug-resistant TB
second-generation aminoglycosides and fluoroquinolones
Extensively drug-resistant TB
drug combos
M. bovis
- cattle and humans
- transmitted via ingestion of contaminated milk or airborne
- closely resembles TB
- low rate in US
- very slow growing
NTMs
- soil and water sources
- opportunistic (lung disease, ICPs)
- resembles TB, some may be cutaneous
- no person-to-person transmission
M. avium complex (MAC complex)
- M. avium and M. intracellulare
- most common NTM causing TB in the US
- slow growing, nonpigmented
- soil and water sources
- disease in swine and poultry
- large increase in number of isolates due to HIV patients developing AIDS (most common systemic disease)
M. avium complex (biochemical tests)
- inactive in most tests
- produce heat-stable catalase
- grow in media containing T2H
- Nucleic acid probes available to identify
- treatment based on empiric data, not susceptibility/ID
Other Slow-growing species
M. paratuberculosis M. kansasii M. genavense M. haemophilum M. malmoense M. marinum M. scrofulaceum M. simiae M. szulgai M. ulcerans M. xenopi M. gordonae
M. paratuberculosis
- Johne’s disease
- niacin -, nitrate -, tween 80 -
M. kansasii
- 2nd most common NTM causing lung disease in US
- CHRONIC PULMONARY DISEASE
- occasionally extrapulmonary
- photochromogenic
- catalase +, Tween 80 +
- reduces nitrate
- pyrazinamidase production
- nucleic acid probe available
Slow growing ID
- slow growth with smooth to rough colonies
- wavy edges and dark centers
- photoreactivity
Photochromogens
- photoreactivity
- carotene pigment upon exposure to light
Scotochromogens
- photoreactivity
- produce a pale yellow to orange color in dark or light
Non chromogenic
- photoreactivity
- buff or lack of color
M. genavense
- disseminated AIDS infection
- enteritis, genital, soft tissue
- SQ and heat-stable catalase +, pyrazinamidase +, urease +
M. haemophilum
- ICPs
- submandibular lymphadenitis, subcutaneous nodules, painful swellings, ulcers, abscesses, draining fistulas
- requires hemoglobin or hemin
M. malmoense
- chronic pulmonary disease
- cervical lymphadenitis
M. marinum
- cutaneous infections
- due to contact with saltwater or inadequately chlorinated freshwater
- “swimming pool granuloma”
M. scrofulaceum
- cervical lymphadenitis in kids
- smooth colonies with dense centers
- light yellow to deep orange pigment
- Tween 80 -, don’t reduce nitrate
- urease +, high SQ catalase
M. simiae
- pulmonary disease
- phochromogenic
- niacin +
M. szulgai
- pulmonary disease
- similar to TB
- photochromogenic
- Tween 80 +, reduces nitrate
- inhibited by NaCl
M. ulcerans
- nodule developing into a severe shallow ulcer
- nonchromogenic buff colonies
- heat-stable catalase
M. xenopi
- hot and cold-water taps, birds
- pulmonary infection in patients with predisposing condition
- scotochromogenic
- niacin - , reduce nitrate
M. gordonae
- tap water and soil sources
- “tap water” bacillus
- nucleic acid probe available
Rapidly Growing Species
M. chelonae
M. fortuitum
M. smegmatis
M. chelonae
- M. abscessus group
- opportunistic
- more drug resistance than M. fortuitum
- positive 3-day arylsulfatase test
- growth on Mac without crystal violet
- doesn’t reduce nitrate
M. fortuitum
- localized infections of skin and soft tissues
- positive 3-day arylsulfatase test
- reduces nitrate
M. smegmatis
- rare cases of pulmonary, skin, soft tissue and bone infections
- nonpigmented colonies
- negative arylsulfatase test
- reduces nitrate
- grows on Mac w/o crystal violet
M. leprae
- Hansen’s disease (leprosy)
- Tuberculoid leprosy and Lepromatous leprosy
- person-to-person transmission
- low infection rate
- can’t be cultured in vitro
- armadillos and foot pads of white mice
Tuberculoid leprosy
- skin lesions and nerve involvement
- spontaneous recovery
Lepromatous leprosy
- skin lesions
- progressive nerve damage
Safety when working with Mycobacteria
- ventilation separate from rest of lab
- biological safety cabinet
- disinfectants
- PPE
Mycobacteria specimen collection
- Respiratory specimens
- sputum (expectorated or induced)
- early morning specimen on 3 consecutive days (2 out of 3 positive is confirmatory)
- gastric aspirate, urine, stool, blood, body fluids, tissue
Digestion/decontamination of specimens
- liquefy sample through digestion of proteinaceous material
- allow chemical decontaminating agent to contact and kill the non-mycobacterial organisms
- mycobacteria survive chemical treatment because of high lipid content in cell walls
- liquefying mucin allows mycobacteria to utilize nutrients
Specimens that need digestion and decontamination
sputum, gastric washing, BAL, bronchial washings, transtracheal aspirate
Specimens that only need decontamination
urine, autopsy tissue, fluids
specimens that don’t need digestion and decontamination
CSF, pleural fluid, joint fluid
Digestion and decontamination agents
- Sodium hydroxide
- N-acetyl-L-cysteine
Mycobacteria staining
- irregular uptake of gram stain because of high lipid content
- light gram-positive if anything
- ACID-FAST STAINING
- Auramine-rhodamine fluorochrome stain
Acid-fast staining
- Ziehl-Neelsen (uses heat)
- Kinyoun (no heating)
Auramine-rhodamine fluorochrome stain
- bright yellow-orange bacilli
- more sensitive
- may miss rapid-growers
Mycobacteria culture media
- Lowenstein-Jensen (LJ) media (also called ATS): eggs, salts, glycerol, potato flour
- Middlebrook media
- all media contain malachite green (suppress gram-positive)
BACTEC system
amount of labeled CO2 liberated is detected by instrument and is interpreted as “growth index”
Mycobacteria Growth Indicator Tube (MGIT)
O2 consumption by organism present in the medium are detected as an increase in fluorescence
Septi-Chek AFB system
- growth is detected by observing paddle
- detection times shorter than conventional media, longer than BACTEC
Mycobacterium ID
- acid fast organism
- colony morphology (smooth and soft or rough)
- growth rates: rapid growers (7 days)
- growth temperature
- photoreactivity
- niacin accumulation (most +)
- nitrate test (M. kansasii and tuberculosis +)
- catalase (M. tb, bovis are -)
- Tween 80 hydrolysis
- iron uptake
- arylsulfatase test
- pyrazinamidase (distinguishes M. marinum (+) from kansasii and M. bovis from tb (+))
- Tellurite reduction (MAC +)
- urease (M. scrofulaceum (+) and gordonae)
Inhibitory tests
- NAP (inhibits M. tb complex)
- T2H (bovis (S) from tb (R))
- NaCl tolerance (M. flavescens and M. triviale grow)
- Growth on MAC agar (M. fortuitum-chelonae complex grow on MAC w/o crystal violet)
M. tuberculosis (Identification)
MTB is only non-pigmented producer that is nitrate + and niacin + in culture media
