microbiology practical

What is the specimen used for diagnosis of Streptococcus pneumoniae?

Sputum.

What is the Gram stain appearance of Streptococcus pneumoniae?

Gram-positive diplococci.

Is Streptococcus pneumoniae spore forming?

No.

Is Streptococcus pneumoniae motile?

No.

Does Streptococcus pneumoniae have a capsule?

Yes, polysaccharide capsule.

What type of hemolysis does Streptococcus pneumoniae produce on blood agar?

Alpha hemolysis.

What is alpha hemolysis?

Partial hemolysis.

What temperature is optimal for growth of Streptococcus pneumoniae?

37°C.

Is Streptococcus pneumoniae aerobic or anaerobic?

Facultative anaerobe.

Does Streptococcus pneumoniae grow better in excess CO₂?

Yes.

Does Streptococcus pneumoniae grow on ordinary media?

No.

What are the colony characteristics of Streptococcus pneumoniae on blood agar?

Small colonies with central depression.

Which biochemical test shows fermentation of inulin?

Inulin fermentation test.

Is Streptococcus pneumoniae bile soluble?

Yes.

Is Streptococcus pneumoniae sensitive to optochin?

Yes.

What is the principle of the optochin sensitivity test?

Pneumococci are sensitive while viridans streptococci are resistant.

What indicates a positive optochin test?

Zone of inhibition around disc.

What is the principle of bile solubility test?

Pneumococci dissolve in bile.

What indicates a positive bile solubility test?

Clearing of the turbid broth.

What is the Quellung reaction?

Capsular swelling after addition of antibodies.

What genus does Mycobacterium tuberculosis belong to?

Mycobacterium.

What diseases are caused by Mycobacterium tuberculosis?

Pulmonary, GI, renal TB, meningitis, bone spread.

What is the reservoir of Mycobacterium tuberculosis?

Humans.

What is the shape of Mycobacterium tuberculosis?

Straight or slightly curved rods.

Is Mycobacterium tuberculosis motile?

No.

Is Mycobacterium tuberculosis spore forming?

No.

What staining property characterizes Mycobacterium tuberculosis?

Acid-fast.

Why is Mycobacterium tuberculosis acid-fast?

High lipid content in cell wall.

What samples are collected for pulmonary TB diagnosis?

Sputum, bronchial or gastric washings.

How many sputum samples are required for TB diagnosis?

At least three morning samples.

Which stain is used for direct smear of TB?

Ziehl-Neelsen stain.

What dye is used as primary stain in ZN stain?

Concentrated carbol fuchsin.

What is used as decolorizer in ZN stain?

Acid alcohol.

What is the counterstain in ZN stain?

Methylene blue.

What is the appearance of acid-fast bacilli after ZN stain?

Red bacilli on blue background.

Is Mycobacterium tuberculosis aerobic or anaerobic?

Obligate aerobe.

What temperature is optimal for Mycobacterium tuberculosis growth?

37°C.

Which media is used for culture of Mycobacterium tuberculosis?

Lowenstein-Jensen medium.

What type of medium is Lowenstein-Jensen?

Enriched selective medium.

How long does Mycobacterium tuberculosis take to grow?

4–8 weeks.

What are the colony characteristics of Mycobacterium tuberculosis?

Dry, rough, raised, grayish colonies.

What animal is used for pathogenicity testing of TB?

Guinea pig.

What rapid culture system is used for TB?

BACTEC system.

What is detected in BACTEC system?

Radio-labeled CO₂.

What modern methods detect TB DNA?

PCR and DNA probes.

What test is used for latent TB diagnosis?

Quantiferon TB test.

What is the tuberculin skin test used for?

Detection of previous TB exposure.

What substance is injected in tuberculin test?

PPD.

What volume is injected in tuberculin test?

0.1 ml.

When is tuberculin test read?

After 48–72 hours.

What indicates a positive tuberculin test?

Induration >10 mm.

What causes false positive tuberculin test?

BCG vaccination, non-TB mycobacteria.

What causes false negative tuberculin test?

Immunosuppression, HIV, malnutrition.

Are fungi aerobic or anaerobic?

Aerobic.

What temperature is used to culture filamentous fungi?

25–27°C.

What temperature is used to culture yeasts?

37°C.

What is the most common fungal culture medium?

Sabouraud dextrose agar.

What is added to SDA to inhibit bacteria?

Chloramphenicol or gentamicin.

What is added to SDA to inhibit opportunistic fungi?

Cycloheximide.

What enriched medium is used for dimorphic fungi?

Brain heart infusion agar.

What is KOH preparation used for?

Digest tissue and clear background.

What stain detects Cryptococcus capsule?

India ink.

What stain is used for fungal morphology?

Lactophenol cotton blue.

Which stains detect invasive fungal infection in tissue?

PAS and Gomori methenamine silver.

What are the colony features of Aspergillus?

Velvety to powdery colonies.

What is the microscopic feature of Aspergillus?

Septated hyphae with dichotomous branching.

What antigen is detected in Aspergillus infection?

Galactomannan.

What fungal cell wall component can be detected in serum?

(1–3)-β-D-glucan.

What are the colony characteristics of Candida albicans?

White creamy smooth colonies.

What is the microscopic appearance of Candida albicans?

Budding yeast with pseudohyphae.

How does Candida albicans appear on Gram stain?

Gram positive.

What test differentiates Candida albicans from other Candida species?

Germ tube test.

At what temperature is germ tube test done?

37°C.

How long does germ tube formation take?

4 hours.