UAMS MICRO CASE STUDY MODULE 4
EXAM QUESTIONS AND ANSWERS
WITH COMPLETE SOLUTIONS
ALREADY PASSED!!!
Mycobacteriology: Transmission, Diagnostic Assays, & Specimen Collection
How is Mycobacterium tuberculosis (MTB) primarily transmitted between
individuals?
✔✔ Inhalation of airborne infectious aerosols (droplet nuclei).
What are the primary characteristics and clinical implications of a positive
Tuberculin Skin Test (TST / PPD)?
✔✔ Physical Finding: A red, indurated (hardened) area at the injection site
measured across its diameter.
✔✔ Clinical Interpretation: Indicates the individual has been exposed to MTB
and may have either latent tuberculosis infection (LTBI) or active TB disease
(does not differentiate between active and latent disease).
What are the key operational features and diagnostic advantages of
Interferon-Gamma Release Assays (IGRAs)?
✔✔ Requires a blood sample (in vitro whole-blood assay).
✔✔ Less subjective to reader bias and measurement errors compared to skin tests.
✔✔ Not affected by prior Bacille Calmette-Guérin (BCG) vaccination
(eliminates false-positive results caused by BCG).
How do Mycobacterium species typically appear on standard Gram-stained
smears?
✔✔ They stain very poorly—if at all (often appearing as faint, ghost-like Gram-
positive or unstained "beaded" bacilli due to the high lipid/mycolic acid content of
their cell walls).
What is the recommended clinical specimen collection protocol for urine
mycobacterial cultures?
,✔✔ Collection of 3 to 5 first-morning clean-catch urine samples obtained on
consecutive days (over one week).
No decontamination-centrifuge and inoculate media
CSF
Decontaminate specimen and inoculate 2 sets of media (30C and 35C)
Skin/wound
no decontamination needed
pleural fluid
decontaminate specimen before inoculating media
sputum and urine
How should gastric aspirated be handled if they cannot be processed within 4 hours
neutralize specimen with sodium bicarbonate
which mycobacteria are rapid growers
M. abscesses and M. fortuitum-chelonae
, how fast does a rapid grower grow
less than 7 days
if the contamination rate is too HIGH
the decontamination process is not strong enough
function of N-acetyl-L-cysteine
mucolytic agent
function of 2% NaOH
Decontaminating agent
requirements for storing middlebrook agar
store in the dark
incubate plates in CO2
Agar based mycobacteria media
Middlebrook 7H10
EXAM QUESTIONS AND ANSWERS
WITH COMPLETE SOLUTIONS
ALREADY PASSED!!!
Mycobacteriology: Transmission, Diagnostic Assays, & Specimen Collection
How is Mycobacterium tuberculosis (MTB) primarily transmitted between
individuals?
✔✔ Inhalation of airborne infectious aerosols (droplet nuclei).
What are the primary characteristics and clinical implications of a positive
Tuberculin Skin Test (TST / PPD)?
✔✔ Physical Finding: A red, indurated (hardened) area at the injection site
measured across its diameter.
✔✔ Clinical Interpretation: Indicates the individual has been exposed to MTB
and may have either latent tuberculosis infection (LTBI) or active TB disease
(does not differentiate between active and latent disease).
What are the key operational features and diagnostic advantages of
Interferon-Gamma Release Assays (IGRAs)?
✔✔ Requires a blood sample (in vitro whole-blood assay).
✔✔ Less subjective to reader bias and measurement errors compared to skin tests.
✔✔ Not affected by prior Bacille Calmette-Guérin (BCG) vaccination
(eliminates false-positive results caused by BCG).
How do Mycobacterium species typically appear on standard Gram-stained
smears?
✔✔ They stain very poorly—if at all (often appearing as faint, ghost-like Gram-
positive or unstained "beaded" bacilli due to the high lipid/mycolic acid content of
their cell walls).
What is the recommended clinical specimen collection protocol for urine
mycobacterial cultures?
,✔✔ Collection of 3 to 5 first-morning clean-catch urine samples obtained on
consecutive days (over one week).
No decontamination-centrifuge and inoculate media
CSF
Decontaminate specimen and inoculate 2 sets of media (30C and 35C)
Skin/wound
no decontamination needed
pleural fluid
decontaminate specimen before inoculating media
sputum and urine
How should gastric aspirated be handled if they cannot be processed within 4 hours
neutralize specimen with sodium bicarbonate
which mycobacteria are rapid growers
M. abscesses and M. fortuitum-chelonae
, how fast does a rapid grower grow
less than 7 days
if the contamination rate is too HIGH
the decontamination process is not strong enough
function of N-acetyl-L-cysteine
mucolytic agent
function of 2% NaOH
Decontaminating agent
requirements for storing middlebrook agar
store in the dark
incubate plates in CO2
Agar based mycobacteria media
Middlebrook 7H10
