UAMS MICROBIOLOGY EXAM 5
QUESTIONS AND ANSWERS WITH
COMPLETE SOLUTIONS 100%
CORRECT!!
Mycobacteriology: Organism Characteristics & Acid-Fast Staining
What are the fundamental cellular characteristics and morphology of the
genus Mycobacterium?
✔✔ Strictly aerobic, non-spore-forming bacilli (rods)
(Slender, slightly curved or straight rods that grow slowly relative to most clinical
bacteria).
What structural property defines Acid-Fast Bacilli (AFB), and how does it
affect standard and specialized staining methods?
✔✔ Cell Wall Composition: Extremely high lipid content (primarily composed
of mycolic acids and complex wax lipids).
✔✔ Gram Stain Behavior: Stains poorly or not at all with routine Gram stains
(often appearing as faint, "ghost-like" rods or Gram-neutral beaded bacilli).
✔✔ Acid-Fast Primary Staining: Primary dyes (such as carbolfuchsin) penetrate
the cell wall with heating or lipophilic solvents and bind to the mycolic acids.
✔✔ Resistance to Decolorization: Once stained, they resist decolorization with
acid-alcohol solutions, retaining the primary dye (appearing bright pink/red
against a blue or green counterstain).
Ziehl-Neelson
Hot method of staining AFB
Carbolfuchsin (steamed 3-5 minutes)
Acid Alcohol
Methylene blue (counterstain)
AFB = red; Other organisms = blue
,Kinyoun
Cold stain
Phenol used to force carbolfuchsin into cell
AFB = red; Other organisms = blue
Fluorescent AFB stain
Auramine O-Rhodamine
Acid alcohol
Potassium permanganate (counterstain, quenches background fluorescence)
AFB = yellow to orange fluorescence
Mycobacterium tuberculosis (MTB)
Most common cause of tuberculosis
Transmitted via the respiratory tract
Spreads throughout body
Cell mediated immunity
Caseating granuloma (tubercle)
Interferon gamma release assay
Detects TB infection and disease in place of skin test
,Measures release of interferon-gamma by WBCs in response to MTB antigens
using a blood sample
Results unaffected by prior BCG vaccination
Primary MTB infection
First time infection
Once infected, MO permanently in body unless treated
Recurrent MTB infection
Reactivation of previous infection
If immunity declines, infection can be reactivated (elderly, HIV patients)
Tuberculosis patients
Elderly
HIV+
immigrants
homeless
immunocompromised
Pulmonary tuberculosis
disease caused by the presence of Mycobacterium tuberculosis in the lungs;
characterized by the formation of tubercles, inflammation, and necrotizing caseous
lesions
, Miliary tuberculosis
the development of active tubercles throughout the body
widespread, disseminated
Scrofula Tuberculosis
transcutaneous inoculation, moves via lymphatics
Other sites of tuberculosis
kidney
bone
liver
meninges
M. bovis
Tuberculosis, transmitted from cattle
Attenuated strain used for BCG vaccine
M. leprae
Leprosy (Hansen's disease)
Cannot grow on artificial media
QUESTIONS AND ANSWERS WITH
COMPLETE SOLUTIONS 100%
CORRECT!!
Mycobacteriology: Organism Characteristics & Acid-Fast Staining
What are the fundamental cellular characteristics and morphology of the
genus Mycobacterium?
✔✔ Strictly aerobic, non-spore-forming bacilli (rods)
(Slender, slightly curved or straight rods that grow slowly relative to most clinical
bacteria).
What structural property defines Acid-Fast Bacilli (AFB), and how does it
affect standard and specialized staining methods?
✔✔ Cell Wall Composition: Extremely high lipid content (primarily composed
of mycolic acids and complex wax lipids).
✔✔ Gram Stain Behavior: Stains poorly or not at all with routine Gram stains
(often appearing as faint, "ghost-like" rods or Gram-neutral beaded bacilli).
✔✔ Acid-Fast Primary Staining: Primary dyes (such as carbolfuchsin) penetrate
the cell wall with heating or lipophilic solvents and bind to the mycolic acids.
✔✔ Resistance to Decolorization: Once stained, they resist decolorization with
acid-alcohol solutions, retaining the primary dye (appearing bright pink/red
against a blue or green counterstain).
Ziehl-Neelson
Hot method of staining AFB
Carbolfuchsin (steamed 3-5 minutes)
Acid Alcohol
Methylene blue (counterstain)
AFB = red; Other organisms = blue
,Kinyoun
Cold stain
Phenol used to force carbolfuchsin into cell
AFB = red; Other organisms = blue
Fluorescent AFB stain
Auramine O-Rhodamine
Acid alcohol
Potassium permanganate (counterstain, quenches background fluorescence)
AFB = yellow to orange fluorescence
Mycobacterium tuberculosis (MTB)
Most common cause of tuberculosis
Transmitted via the respiratory tract
Spreads throughout body
Cell mediated immunity
Caseating granuloma (tubercle)
Interferon gamma release assay
Detects TB infection and disease in place of skin test
,Measures release of interferon-gamma by WBCs in response to MTB antigens
using a blood sample
Results unaffected by prior BCG vaccination
Primary MTB infection
First time infection
Once infected, MO permanently in body unless treated
Recurrent MTB infection
Reactivation of previous infection
If immunity declines, infection can be reactivated (elderly, HIV patients)
Tuberculosis patients
Elderly
HIV+
immigrants
homeless
immunocompromised
Pulmonary tuberculosis
disease caused by the presence of Mycobacterium tuberculosis in the lungs;
characterized by the formation of tubercles, inflammation, and necrotizing caseous
lesions
, Miliary tuberculosis
the development of active tubercles throughout the body
widespread, disseminated
Scrofula Tuberculosis
transcutaneous inoculation, moves via lymphatics
Other sites of tuberculosis
kidney
bone
liver
meninges
M. bovis
Tuberculosis, transmitted from cattle
Attenuated strain used for BCG vaccine
M. leprae
Leprosy (Hansen's disease)
Cannot grow on artificial media
