Microbiology Lab Quiz 10 Practice

What is innate (non-specific) immunity?

The body's first defense that attacks any invader using WBCs and chemicals. Discovered by Elie Metchnikoff (1883).

What is adaptive (specific) immunity?

Targets specific microorganisms using antibodies. First shown by Emil von Behring (1894).

What is an antigen?

A molecule that triggers an immune response to produce antibodies.

What is an antibody?

A protein made by plasma cells that binds to and neutralizes pathogens.

What is agglutination?

Clumping reaction between antigens on cells and antibodies; used to identify bacteria.

What is an antiserum?

Blood serum containing antibodies that provides passive immunity.

What do red blood cells do?

Transport oxygen.

What do white blood cells do?

Defend against infection.

What do platelets do?

Help with clotting.

What is plasma?

Fluid part of blood containing fibrinogen.

What is serum?

Fluid left after clotting; lacks fibrinogen.

What is fibrinogen?

Protein precursor that forms fibrin for blood clots.

What is hemagglutination?

Clumping of red blood cells when antibodies react with surface antigens.

What is the Rh factor?

A protein antigen (D antigen) used in blood typing.

How is the Rh factor detected?

By mixing RBCs with anti-D antiserum — agglutination = Rh positive.

When does Rh incompatibility happen?

When the mother is Rh- and the baby is Rh+.

Why is Rh incompatibility dangerous?

Mother's anti-D antibodies can cross placenta and destroy baby's RBCs → hemolysis, jaundice, anemia.

How can Rh incompatibility be prevented?

IM injection of RhoGAM (anti-D antibodies) after sensitizing events.

Why is the skin inhospitable to most microbes?

Sebum inhibits growth, sweat creates a salty environment, and dry keratin layers limit survival.

What is the normal microbiota of the skin?

Bacteria adapted to dryness and high salt; common in moist areas like the nose and armpits.

What is transient microbiota?

Temporary microbes acquired from environmental contact.

What is Propionibacterium and what does it do?

Lives in hair follicles; produces propionic acid → lowers pH and inhibits other bacteria (helps cause acne).

What enzyme is produced by all Staphylococcus species?

Catalase — breaks down hydrogen peroxide into water and oxygen.

What does the coagulase enzyme do?

Clots fibrin to help bacteria evade the immune system.

What color are Staphylococcus epidermidis colonies?

White (small colonies).

Is Staphylococcus epidermidis coagulase positive or negative?

Coagulase negative (-).

Can Staphylococcus epidermidis ferment mannitol?

No — it cannot ferment mannitol.

What color are Staphylococcus aureus colonies?

Golden yellow colonies

Is Staphylococcus aureus coagulase positive or negative?

Coagulase positive (+).

Can Staphylococcus aureus ferment mannitol?

Yes — it ferments mannitol.

What is MRSA?

Methicillin-resistant S. aureus; confirmed by Kirby-Bauer or RT-PCR.

What does Mannitol Salt Agar (MSA) test for?

Selects for salt-tolerant bacteria and differentiates mannitol fermenters. Fermentation → acid → phenol red indicator turns yellow.

What are the main steps of the skin bacteria lab?

Label plate → swab skin → streak sections → flame loop before/after → keep plate closed.