Acid-fast Bacteria Flashcards
Rod-shaped, aerobic bacteria that do not form spores.
They are difficult to be stained by ordinary stain due to the high content of lipoid substances in the cell wall
Mycobacterium
causes tuberculosis and is a very important pathogen of humans.
M tuberculosis
Causes leprosy
Mycobacterium leprae
Frequently infect patients with AIDS, are opportunistic pathogens in other immunocompromised persons, and occasionally cause disease in patients with normal immune systems.
- Mycobacterium avium-intracellulare (M avium complex, or MAC)
- other nontuberculous mycobacteria (NTM)
The media for primary culture of mycobacteria
nonselective medium and a selective medium.
Are useful for observing colony morphology, for detection of mixed cultures, for antimicrobial susceptibility testing, and can also provide some indication of the quantity of organisms in a particular specimen.
Agar-based (solid) media
Obligate aerobes and derive energy from the oxidation of many simple carbon compounds
Mycobacterium
Enhances grow rate since they have slower growth rate than most bacteria
Increased CO2 tension
The doubling time of tubercle bacilli
18 hours
Tend to be more resistant to chemical agents than other bacteria because of the hydrophobic nature of the cell surface and their clumped growth.
Mycobacteria
Are resistant to drying and survive for long periods in dried sputum
Tubercle bacilli
Are emitted in droplets smaller than 25 um in diameter when infected persons cough, sneeze, or speak.
Mycobacteria
What happens inside the alveoli after Mycobacteria enters the host
The host’s immune system responds by release of cytokines and lymphokines that stimulate monocytes and macrophages.
Appear in the lung 1–2 months after exposure.
Pathogenic lesions associated with infection
The production and development of lesions and their healing or progression are determined chiefly by
(1) the number of mycobacteria in the inoculum and their subsequent multiplication
(2) the type of host and immune response
Two Principal Lesions
of Mycobacterium
Exudative type
Productive (proliferative) type
When fully developed, this productive type of lesion, a chronic granuloma, consists of three zones:
- a central area of large, multinucleated giant cells containing tubercle bacilli;
- a mid zone of pale epithelioid cells, often arranged radially
- a peripheral zone of fibroblasts, lymphocytes, and monocytes.
Later, peripheral fibrous tissue develops, and the central area undergoes caseation necrosis
tubercle
Clinical manifestation of Tubercle bacillus
protean
Can occur in the absence of other signs of tuberculosis
Meningitis or urinary tract involvement
Bloodstream dissemination leads to ______ with lesions in many organs and a high mortality rate.
miliary tuberculosis
Specimens of M tuberculosis
fresh sputum, gastric washings, urine, pleural fluid, cerebrospinal fluid, joint fluid, biopsy material, blood, or other suspected material
Specimens from sputum and other nonsterile sites should be liquefied with __________, neutralized with _____, and concentrated by _______.
- N-acetyl-L-cysteine decontaminated with NaOH (kills many other bacteria and fungi)
- buffer
- centrifugation
Specimens from sterile sites, such as cerebrospinal fluid can be directly
Centrifuged, examined, and cultured.
Stains of gastric washings and urine generally are not recommended because
saprophytic mycobacteria may be present and yield a positive stain.
Is more sensitive than traditional acid-fast stains, such as Ziehl-Neelsen, and is the preferred method for clinical material of tubercle bacilli
Fluorescence microscopy with auramine-rhodamine stain
Is the most sensitive method and provides results most rapidly.
Selective broth culture
Incubation for myvobacterial infection
35–37°C in 5–10% CO2 for up to 8 weeks
If culture results are negative in the setting of a positive acid-fast stain or if slowly growing NTM are suspected, then a set of inoculated media should be incubated
at a lower temperature (eg, 24–33°C) and both sets incubated for 12 weeks.
Produce pigment in light but not in darkness
Photochromogens
Develop pigment when growing in the dark
Scotochromogens
Are nonpigmented or have light tan or buff-colored colonies.
Nonchromogens (nonphotochromogens)
The two major drugs used to treat tuberculosis
INH and RMP
The other first-line drugs in treating tuberculosis
pyrazinamide (PZA) and ethambutol (EMB)
If the isolate is susceptible to INH and RMP, PZA and EMB can be discontinued, and the remaining treatment
with INH and RMP is continued to complete a 6-month course.
Most frequent source of infection of tuberculosis is
humans
Infection occurs at an earlier age in
urban than in rural populations.
T/F
Patients who have had tuberculosis can be infected exogenously a second time.
True
Endogenous reactivation tuberculosis occurs most commonly among persons with
AIDS immunosuppression and elderly malnourished or alcoholic destitute men
