MCB 2010C Microbiology Laboratory Midterm Review

Comprehensive practice flashcards for the MCB 2010C Microbiology Laboratory Midterm, covering microscope usage, staining, media interpretation, and laboratory techniques.

What are the four common objective lenses found on a compound microscope?

$4 \times$, $10 \times$, $40 \times$, and $100 \times$

How is total magnification calculated on a microscope?

By multiplying the ocular magnification ($10 \times$) by the magnification of the objective lens used.

What is the total magnification when using the low-power ($4 \times$) objective lens?

$$40 \times$$

What is the total magnification when using the medium-power ($10 \times$) objective lens?

$$100 \times$$

What is the total magnification when using the high-dry ($40 \times$) objective lens?

$$400 \times$$

What is the total magnification when using the oil immersion ($100 \times$) objective lens?

$$1000 \times$$

Which objective lens specifically requires the use of immersion oil?

$$100 \times$$

What does numerical aperture measure in microscopy?

The light-gathering ability of the objective lens.

What is resolution in the context of a compound microscope?

The ability to distinguish two adjacent points as separate and distinct.

What is the correct order of reagents used in Gram staining?

Crystal violet → Gram's iodine → Decolorizer → Safranin

What is the first reagent used in the Gram stain procedure?

Crystal violet

What is the second reagent used in the Gram stain procedure?

Gram's iodine

What is the third reagent used in the Gram stain procedure?

Decolorizer

What is the fourth and final reagent used in the Gram stain procedure?

Safranin

What is the function of Crystal violet in Gram staining?

It acts as the primary stain, coloring all cells purple.

What is the function of Gram's iodine in Gram staining?

It acts as a mordant to fix the dye in the cell wall.

What is the function of the Decolorizer in Gram staining?

It removes the primary stain from Gram-negative cells.

What is the function of Safranin in Gram staining?

It acts as a counterstain, coloring decoupled Gram-negative cells pink or red.

Gram staining is used to differentiate between which two types of bacteria?

Gram-positive and Gram-negative bacteria

What are the three types of hemolysis that can be identified on Columbia CNA Blood Agar?

Alpha, beta, and gamma hemolysis

What characterizes alpha hemolysis on blood agar?

Partial destruction of red blood cells, often appearing as a greenish discoloration.

What characterizes beta hemolysis on blood agar?

Complete destruction of red blood cells, resulting in a clear zone around the colonies.

What characterizes gamma hemolysis on blood agar?

No destruction of red blood cells, appearing as simple growth with no change to the medium.

What is the purpose of the CNA in Columbia CNA Blood Agar?

It makes the medium selective by inhibiting the growth of certain organisms.

What do yellow colonies on Hektoen Enteric (HE) Agar indicate?

Lactose fermentation

What do green colonies on Hektoen Enteric (HE) Agar indicate?

The organism is a non-fermenter.

What do black colonies or black centers on Hektoen Enteric (HE) Agar indicate?

$H_2S$ (hydrogen sulfide) production

Which metabolic process is recognized by a color change to yellow on HE agar?

Lactose fermentation

Which metabolic process causes a black precipitate in HE agar?

$H_2S$ production

What is being tested in a starch hydrolysis test?

The ability of an organism to produce amylase to break down starch.

What is being tested in a DNA hydrolysis test?

The ability of an organism to produce DNase to break down DNA.

What is being tested in a tributyrin hydrolysis test?

The ability of an organism to produce lipase to break down lipids (tributyrin).

What is being tested in a casein hydrolysis test?

The ability of an organism to produce casease to break down milk protein (casein).

What is the purpose of Fluid Thioglycollate Medium (FTM)?

To determine the oxygen requirements of a microorganism.

How is an obligate aerobe defined in FTM?

An organism that requires oxygen and grows only at the top of the medium.

How is an obligate anaerobe defined in FTM?

An organism that cannot survive in oxygen and grows only at the bottom of the medium.

How is a facultative anaerobe defined in FTM?

An organism that can grow with or without oxygen, but grows better in its presence.

How is a microaerophile defined in FTM?

An organism that requires a reduced level of oxygen for growth.

How is an aerotolerant anaerobe defined in FTM?

An organism that does not use oxygen but is not affected by its presence.

What reagent is used to perform the Catalase Test?

Hydrogen peroxide ($H_2O_2$)

What constitutes a positive reaction in the Catalase Test?

The rapid production of bubbles.

What constitutes a negative reaction in the Catalase Test?

An absence of bubble production.

What are the first two reagents added to the Nitrate Reduction Test?

Reagent A and Reagent B

If a nitrate test turns red after adding Reagents A and B, what is the result?

Positive for nitrate reduction to nitrite ($NO_2^-$).

What is the purpose of adding zinc powder to a Nitrate Reduction Test?

To determine if nitrate ($NO_3^-$) is still present in the tube after no color change occurred with Reagents A and B.

In a Nitrate Reduction Test, what does it mean if the medium turns red after adding zinc powder?

The result is negative; nitrate was still present and was reduced by the zinc, not the bacteria.

In a Nitrate Reduction Test, what does it mean if the medium remains colorless after adding zinc powder?

The result is positive; nitrate was reduced beyond nitrite to nitrogen gas ($N_2$) or other non-nitrite products.

What gas is being identified if it appears in the Durham tube during a nitrate test?

Nitrogen gas ($N_2$)

What does 'K/A' represent in a Kligler Iron Agar (KIA) interpretation?

Alkaline slant (red) / Acid butt (yellow)

What does 'A/A' represent in a Kligler Iron Agar (KIA) interpretation?

Acid slant (yellow) / Acid butt (yellow)

What does a black precipitate in the bottom of a KIA tube indicate?

$H_2S$ (hydrogen sulfide) production

How is gas production visualized in a Kligler Iron Agar (KIA) tube?

Cracks or lifting of the agar.

What does TSA stand for?

Tryptic Soy Agar

What does MSA stand for?

Mannitol Salt Agar

What is the primary difference between selective and differential media?

Selective media inhibit the growth of specific microbes; differential media distinguish between different microbes based on metabolic reactions.

What is a pure culture?

A laboratory culture containing only a single species of microorganism.

What is the purpose of a quadrant streak?

To isolate individual colonies from a mixed culture to obtain a pure culture.

What is the purpose of heat fixing a slide during staining?

To kill the bacteria and permanently adhere them to the microscope slide.

What is aseptic technique?

A set of specific practices used to prevent contamination of cultures, the environment, and the researcher.

What does the abbreviation BSL-2 stand for?

Biosafety Level 2

How are bacteria classified based on their growth at different temperatures?

Temperature classifications (e.g., psychrophiles, mesophiles, thermophiles)

Why must the mouth of a culture tube be flamed before inoculation?

To create convection currents that prevent airborne contaminants from entering the tube.

Why must the mouth of a culture tube be flamed again after inoculation?

To ensure any microbes at the opening are killed and the environment remains sterile before recapping.

On Columbia CNA agar, what is the role of the blood?

It acts as a differential agent to identify hemolytic activity.

What is the function of immersion oil in microscopy?

It reduces light refraction and increases the numerical aperture and resolution at high magnification ($1000 \times$).

Is TSA considered a selective or differential medium?

Neither; it is a general-purpose growth medium.

Is MSA considered a selective or differential medium?

Both selective (due to high salt) and differential (due to mannitol fermentation).

In Gram staining, what happens if the decolorizer is left on for too long?

Gram-positive cells may lose their purple color and appear Gram-negative (pink).

In Gram staining, what happens if the decolorizer is not left on long enough?

Gram-negative cells may retain the purple color and appear Gram-positive.

What specific reagent identifies the presence of starch in a hydrolysis test?

Iodine (added after incubation)

What does a clear zone around growth on a starch agar plate after adding iodine indicate?

A positive result for starch hydrolysis (amylase present).

What does a clear zone around growth on a tributyrin agar plate indicate?

A positive result for lipid hydrolysis (lipase present).

What does a clear zone around growth on a casein (milk) agar plate indicate?

A positive result for casein hydrolysis (casease present).

What does a clear zone around growth on a DNA agar plate indicate?

A positive result for DNA hydrolysis (DNase present).

Which objective lens has the smallest field of view?

The $100 \times$ objective lens.

In which hydrolysis test is the medium initially opaque or cloudy?

Casein (milk) or Tributyrin agar.

What is the color of nitrite ($NO_2^-$) when it reacts with Nitrate Reagents A and B?

Red

In KIA, if both slant and butt are yellow, which sugars were fermented?

Glucose and lactose.

In KIA, if only the butt is yellow and the slant is red, which sugar was fermented?

Glucose only.

What is the primary purpose of identifying microscope parts and functions for the midterm?

To demonstrate proper operation and care of the instrument.

Which hemolysis type results in a 'clearing' of the agar around growth?

Beta hemolysis

Which hemolysis type results in 'greening' of the agar around growth?

Alpha hemolysis

Does Hektoen Enteric agar inhibit the growth of Gram-positive bacteria?

Yes, it is selective for Gram-negative enteric organisms.

What does 'A' stand for in KIA results?

Acidic (usually yellow due to fermentation).

What does 'K' stand for in KIA results?

Alkaline (usually red due to peptone utilization).

What is the indicator in Fluid Thioglycollate Medium that shows where oxygen is present?

Resazurin (turns pink in the presence of oxygen).

In the Catalase Test, what is being broken down into water and oxygen gas?

Hydrogen peroxide ($H_2O_2$).

Which temperature classification describes bacteria that grow best at human body temperature ($37 \, ^\circ C$)?

Mesophiles

What is the goal of the first quadrant of a quadrant streak?

To deposit the initial heavy amount of inoculum.

What is the result when oxygen is present at the very top of an FTM tube?

A pink layer (if resazurin is used).