Metabolic Activities of Bacteria and the Fungi, Yeasts, and Molds

Exercises
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May 27, 2023
Exercise 4: Some metabolic activities of bacteria
1 The color of phenol red at an acid pH is yellow.
2 A Durham tube's function is to detect gas production during bacterial fermentation. If gas is produced, it will collect in the Durham tube, causing it to bubble or rise.
3 Iodine detects starch hydrolysis because it forms a complex with starch, producing a dark blue or black color. When bacteria secrete enzymes like amylase to break down starch, the presence of iodine helps visualize the areas where starch has been hydrolyzed.
4 Indole is produced in SIM (Sulfide, Indole, Motility) medium through the hydrolysis of tryptophan by the enzyme tryptophanase, produced by certain bacteria. To detect indole production, Kovac's reagent (a mixture of p-dimethylamino benzaldehyde and hydrochloric acid) is added to the medium (Sutami et al., 2021). If indole is present, it reacts with the reagent to produce a cherry-red color.
5 Hydrogen sulfide is demonstrated in SIM medium by reducing sulfur-containing compounds by bacteria. This reduction produces hydrogen sulfide gas, which reacts with iron in the medium to form a black precipitate called ferrous sulfide. The presence of ferrous sulfide indicates hydrogen sulfide production by the bacteria.
Exercise 5: Fungi, yeasts, and molds
1 Viewing mold structures in a transparent tape preparation allows easy observation of their morphology and arrangement without complex staining procedures. The transparency of the tape allows light to pass through, making it easier to visualize the fungal structures under a microscope.
2 Candida albicans can be reliably identified using the germ tube test. This test involves incubating yeast cells in human serum at 37°C. If germ tubes (elongated projections) emerge from the yeast cells after a specified incubation time, it indicates Candida albicans (Hemaid et al., 2021).
3 Three stains ...