Inhibition of Microbial Growth and Microbial Metabolism

Comprehensive practice questions covering microbial growth inhibition, antibiotic sensitivity, and metabolic assays including catalase, oxidase, and hydrolytic enzymes.

What is the primary purpose of the Kirby-Bauer Method in clinical microbiology laboratories?

It is a standardized method used to determine which antimicrobial drugs would be effective for treating an infectious disease.

Who was the German doctor that discovered Arsphenamine (Salvarsan) as a treatment for syphilis in the early 1900s?

Paul Erlich

In 1928, which British physician discovered that a mold contaminated a plate and inhibited the growth of staphylococci?

Alexander Fleming

How should forceps be sterilized according to the laboratory procedure?

Dip the tips in ethanol and briefly pass them through a flame to ignite the alcohol, then wait for the flame to burn out and for the forceps to cool.

At what temperatures should Pseudomonas flourescens and Staphylococcus epidermidis plates be incubated?

Pseudomonas flourescens at room temperature and Staphylococcus epidermidis at $37^\circ\text{C}$.

What mathematical formula is used to find the diameter of a zone of inhibition if only the radius is visible?

$$\text{Radius} \times 2 = \text{diameter}$$

What is the difference between an endoenzyme and an extracellular enzyme?

Extracellular enzymes act outside the cell to degrade large molecules, while endoenzymes act inside the cell to synthesize or degrade molecules.

What are inducible (adaptive) enzymes?

Enzymes that are produced only if the appropriate substrate is available, such as $\beta$-galactosidase.

In the context of microbiology, what is the difference between morphology and physiology?

Morphology is the study of cell size, shape, and arrangement, while physiology is the study of an organism's metabolic capabilities and functions.

What color change indicates a positive result in a cytochrome c oxidase assay?

The reagent (tetramethyl-p-phenylenediamine dihydrochloride) will turn bright blue/purple.

What is the chemical reaction catalyzed by the enzyme catalase?

$$2H_2O_2 \rightarrow 2H_2O + O_2$$

Why does Chlamydomonas reinhardtii require a functional cytochrome oxidase to grow on HSA medium in the dark?

Because it relies on aerobic respiration using acetate as an electron source when light is not available for photosynthesis.

What is the function of a Durham tube in nitrate broth?

It is a small inverted glass tube used to trap dinitrogen ($N_2$) and nitrous oxide ($N_2O$) gases produced during denitrification.

In the nitrate reduction test, what does a red color after adding zinc dust indicate?

It indicates a negative result for nitrate reduction by the bacteria, as the zinc reacted with unused nitrate ($NO_3^-$) to produce nitrite ($NO_2^-$).

What are the pH-dependent color changes for phenol red in carbohydrate fermentation broths?

Bright yellow indicates pH below $6.8$ (acidic), orange-red indicates neutral pH ($6.8$-$8.2$), and bright pink indicates pH above $8.2$ (alkaline).

How is amylase production detected on a starch agar plate?

By flooding the plate with iodine; a clear zone of hydrolysis around a colony indicates starch was broken down by amylase, while the rest of the plate turns brown.

What protein gives milk its opaque appearance and is used to test for the production of the protease caseinase?

Casein

What reagent is added to a gelatin agar plate to demonstrate gelatinase production through precipitation?

Hydrochloric acid ($HCl$)

What three products are released from the metabolic breakdown of cysteine by cysteine desulfhydrase?

Ammonia ($NH_3$), pyruvate ($CH_3-C-C-OH$), and hydrogen sulfide gas ($H_2S$).

What indicates a positive result for hydrogen sulfide production in peptone iron agar?

The formation of a black insoluble precipitate known as ferrous sulfide ($FeS$).