AFB clibac lab - midterm real

Primary stain used in AFB staining

Carbolfuchsin

Decolorizer used in AFB staining

Acid alcohol

Counterstain used in AFB staining

Methylene blue

Mnemonic for AFB staining reagents

CAM (Carbolfuchsin, Acid alcohol, Methylene blue)

AFB staining method that uses heat

Ziehl-Neelsen method

AFB staining method that does NOT use heat

Kinyoun method

AFB staining method using fluorescent dye

Auramine-Rhodamine method

Color of AFB in Ziehl-Neelsen stain

Red or pink

Color of non-acid-fast organisms

Blue

Color of AFB in fluorescent staining

Yellow or orange

Reason for acid-fastness

Mycolic acid in cell wall

Nature of mycolic acid

Hydrophobic lipid

AFB characteristic due to mycolic acid

Resistance to decolorization by acid alcohol

Minimum number of fields to declare negative

300 oil immersion fields

Number of fields typically counted if positive

At least 100 fields

Best specimen for AFB smear

Early morning sputum

Worst specimen for AFB smear

Saliva

Macroscopic appearance of good sputum

Yellowish muco-purulent

Minimum acceptable sputum volume

1 mL

Ideal sputum volume for DSSM

5-10 mL

Cells indicating good sputum quality

Alveolar macrophages (dust cells)

Cells indicating contamination

Oropharyngeal epithelial cells

Meaning of dust cells

Macrophages from deep lung tissue

Interpretation of salivary specimen

Poor quality specimen

Shape and classification of MTB

Acid-fast bacilli

Oxygen requirement of MTB

Strict aerobe

Optimal CO2 condition for MTB growth

5-10% CO2

Growth characteristic of MTB

Slow-growing

Culture medium for MTB

Lowenstein-Jensen medium

Colony appearance of MTB

Buff-colored, nonpigmented

Primary mode of TB transmission

Inhalation of droplets

Activities that spread TB

Coughing, sneezing, talking, singing, spitting

Meaning of DOTS

Directly Observed Treatment Short Course

Purpose of DOTS

TB control and treatment strategy

Definition of AFB positive smear

At least one smear positive

Definition of AFB negative smear

Both smears negative

Action if smear result is doubtful

Repeat sputum examination

Action if smear is negative

Refer for chest X-ray

Action if smear is positive

Start treatment / refer to physician

Survival of MTB in dried sputum

6-8 months

Survival of MTB in air droplets

8-10 days

Effect of sunlight on MTB in culture

Killed in about 2 hours

Effect of sunlight on MTB in sputum

Requires 20-30 hours to be killed

Resistance of MTB to disinfectants

Highly resistant

Chemical needed to kill MTB

5% phenol for 24 hours

Method that easily kills MTB

Moist heat (boiling 10 minutes)

Other method to kill MTB

Autoclaving

Key structural feature of AFB cell wall

High lipid content (>60%)

Effect of lipid-rich cell wall

Low permeability to stains and chemicals

Reason AFB retain primary stain

Strong binding of carbolfuchsin to mycolic acid

Microscopic appearance of AFB

Thin red rods, sometimes beaded

Possible forms of AFB

Beaded, filamentous, clumped

Proper smear thickness

Text readable through smear

Proper smear size

3 cm by 2 cm

Scanning pattern for smear reading

Horizontal systematic scanning

Reason 300 fields are required

To confirm absence of AFB reliably

Main diagnostic tool for TB

Direct sputum smear microscopy (DSSM)

Most accurate TB diagnostic method

Culture