Microbiology Lab Quiz 2: Bacterial Behavior, Metabolism, and Growth

Comprehensive practice question-and-answer flashcards covering bacterial behavior, differential metabolism assays, enzymatic detoxification of oxygen, and oxygen requirement categories from Microbiology Lab Quiz 2.

Why must motility deeps be inoculated by stabbing in a straight line with a needle?

To see where the bacteria moves and avoid getting a false positive result.

What visual result in a motility deep indicates a negative result, and what does it signify?

A crisp, straight stab line, which indicates nonmotile bacteria.

What visual result in a motility deep indicates a positive result, and what does it signify?

A blurry line or cloudy area spreading out from the stab line, which indicates motile bacteria.

Why do bacteria form endospores?

Endospores help cells survive harsh conditions such as lack of nutrients, high temperatures, certain chemicals, and UV radiation.

In quorum sensing (such as bioluminescence regulation), what molecular condition is needed to turn on gene expression?

A high density of autoinducers is required to bind receptors and initiate transcription.

Why do bacteria use quorum sensing to regulate bioluminescence instead of constantly glowing?

Cells do not want to waste their energy and only activate the genes when high cell density is present.

What enzyme is tested for in a urea plate, and what does a positive reaction look like?

It tests for urease; a positive reaction raises the pH and turns the plate pink.

What enzyme is tested for in a citrate plate, and what does a positive reaction look like?

It tests for citrate permease; a positive reaction raises the pH and turns the plate blue.

What enzyme does a gelatin tube test for, and how are positive and negative results distinguished?

It tests for gelatinase. If the tube remains liquid after removal from an ice bath, it is positive ($+$); if it turns solid, it is negative ($-$).

What enzyme does a starch plate test for, and what indicates a positive result following the addition of iodine on day 2?

It tests for amylase; a clearing zone around bacterial growth after flooding with iodine indicates an amylase-positive ($+$) result.

What specific enzyme is detected in the bacterial oxidase test?

Cytochrome c oxidase.

What reaction does superoxide dismutase (SOD) catalyze inside a bacterial cell?

It breaks down toxic superoxide anions into hydrogen peroxide ($H_2O_2$).

What reaction does catalase catalyze inside a bacterial cell?

It breaks down hydrogen peroxide ($H_2O_2$) into water ($H_2O$) and oxygen gas ($O_2$).

What is observed when hydrogen peroxide reagent is added to a catalase-positive bacterium versus a catalase-negative bacterium?

Catalase-positive bacteria produce bubbles from oxygen gas release, whereas catalase-negative bacteria show no reaction.

Why is thioglycolate broth used to evaluate bacterial oxygen requirements?

It creates an oxygen concentration gradient that has higher oxygen at the top and lower oxygen at the bottom, differentiating aerobic and anaerobic growth.

What is the purpose of using a Brewer's jar and GasPak?

It creates an environment that removes oxygen so that anaerobic bacteria can grow.

What is an obligate aerobe?

An organism that requires oxygen to survive and uses it for making ATP.

What is an obligate anaerobe?

An organism that cannot use oxygen and will die if exposed to it.

What is a facultative anaerobe?

An organism that can grow with or without oxygen, switching how it makes energy.

What is an aerotolerant anaerobe?

An organism that does not use oxygen for energy but is not harmed by its presence.