Medical Bacteriology Lab Final

What type of waste goes in biohazard disposal?

Contaminated plates, gloves, swabs, pipette tips, tubes with bacteria.

Where do sharps go?

Sharps container (needles, slides, broken contaminated glass).

Why do we store test results at 4°C?

To slow bacterial metabolism, prevent overgrowth, and preserve color reactions.

What is the purpose of the streak plate method?

To isolate single colonies and obtain a pure culture.

How do you differentiate Enterococcus from S. bovis?

Enterococcus grows in 6.5% NaCl; S. bovis does not. Both are bile-esculin positive.

Why is it clinically important to tell Enterococcus from S. bovis?

Enterococcus often has high-level antibiotic resistance.

What are the key characteristics of S. pyogenes?

β-hemolytic, catalase –, PYR +, Group A Strep.

What tests identify S. aureus?

Catalase +, coagulase +, MSA yellow, β-hemolysis.

What is MRSA and how is it detected?

Methicillin-resistant S. aureus; detected via chromogenic agar.

What identifies S. agalactiae?

CAMP + (arrowhead hemolysis), Group B Strep, β-hemolytic.

What identifies S. pneumoniae?

α-hemolytic, optochin sensitive, bile soluble, has capsule.

What genus is acid-fast and slow-growing?

Mycobacterium.

Name two spore-forming genera.

Bacillus and Clostridium.

Name two capsule-forming bacteria.

Klebsiella pneumoniae, Streptococcus pneumoniae.

What does a positive bile-esculin test look like?

Blackening of the media.

What does bile-esculin positivity indicate?

Enterococcus or Group D Streptococcus (S. bovis).

What does growth in 6.5% NaCl indicate?

Enterococcus (salt tolerant).

What does no growth mean on 6.5% NaCl?

S. bovis or other non-enterococci.

What color indicates a positive PYR test?

Red within 1–2 minutes.

Which organisms are PYR positive?

S. pyogenes and Enterococcus.

What does a positive CAMP test look like?

Arrowhead-shaped enhanced hemolysis.

Which organism is CAMP positive?

S. agalactiae (Group B Strep).

What color indicates oxidase positivity?

Dark purple within 10 seconds.

Name an oxidase-positive genus.

Pseudomonas (also Neisseria, Vibrio).

What does yellow media on MSA indicate?

Mannitol fermentation → S. aureus.

Which Staph grows on MSA but stays pink?

S. epidermidis.

What indicates a positive coagulase test?

Clot formation.

What organism is coagulase positive?

Staphylococcus aureus.

What does bubbling indicate in a catalase test?

Catalase positive (Staphylococci).

What does no bubbling indicate in a catalase test?

Catalase negative (Streptococci).

What does a capsule look like in a capsule stain?

Clear halo around the cell with a dark background.

How do spores and cells appear in a spore stain?

Spores = green; vegetative cells = red.

What color are acid-fast bacteria?

Pink/red.

What genus does this identify?

Mycobacterium.

What color is Gram-positive?

Purple.

What color is Gram-negative?

Pink/red.

What indicates a positive motility test?

Red pigment spread throughout the tube.

What indicates non-motility?

Red only along the stab line.

What does a large zone of inhibition mean?

High susceptibility to the antibiotic.

What does no zone of inhibition mean?

Resistance.

How do you read an MIC strip?

MIC is the number where the ellipse of no growth touches the strip.

What does a metallic green sheen on EMB indicate?

Strong lactose fermentation (E. coli).

What do colorless colonies indicate on an EMB?

Non-lactose fermenter.

What CFU/mL indicates infection?

>100,000 CFU/mL.

What does K/A indicate on TSI?

Glucose fermentation only.

What does A/A indicate on TSI?

Lactose and/or sucrose fermentation.

What does black precipitate indicate on TSI?

H₂S production.

What do cracks/lifting indicate on TSI?

Gas production.

What indicates a positive VP test?

Red color (acetoin production).

What does a blue slant on citrate agar indicate?

Citrate utilization (+).

What does blue color in malonate broth indicate?

Malonate utilization (+).

Why is mineral oil added to decarboxylase tests?

To create anaerobic conditions for enzyme induction.

What color means decarboxylase positive?

Purple.

What color is negative for decarboxylase?

Yellow.

What reagent is used in the indole test?

Kovac’s reagent.

What indicates indole positivity?

Red layer forms on top.

What does a red MR test indicate?

Mixed-acid fermentation (+).

What does the API test generate?

A 7-digit biochemical profile code for bacterial ID.

What does visible clumping indicate in a coagglutination test?

Positive for Group B Strep (S. agalactiae).

What does the RPR test detect?

Reagin antibodies (non-treponemal) for syphilis screening.

What indicates a positive RPR?

Black clumping/flocculation.

What does ELISA detect?

Antigen or antibody using enzyme-linked reactions.

What does a blue color indicate in an ELISA?

Positive reaction due to HRP enzyme activity.

Voges-Proskauer reagent(s)?

α-naphathol & KOH.

Phenylalanine test reagent?

Ferric chloride.

Catalase test reagent?

Hydrogen peroxide.