11 Morphological Characterization of Bacteria - MicroCore RC

Which of the following is a gelatinous polymer of polysaccharides that forms either as a capsule or slime layer?

• exopolysaccharide

• metachromatic granules

• glycolipid

• glycocalyx

Answer explanation

Answer: D. A glycocalyx, literally meaning "sugar coat" (glykys = sweet, kalyx = husk), is a network of polysaccharides that project from cellular surfaces of bacteria, which classifies it as a universal surface component of a bacterial cell, found just outside the bacterial cell wall.

Reference: Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

You performed a flagellar stain with your18 hr-old Escherichia coli culture. Which part of the flagella could you observe as a long whip-like structure?

• Filament

• Basal body

• Hook

• MS rings

Answer explanation

Answer: A. The bacterial flagellar filament is an extracellular tubular protein structure that acts as a propeller for bacterial swimming motility.

Reference: Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

Which of the following is not found in Gram-positive bacteria?

• N-acetylglucosamine

• Lipid A

• Murein

• Teichoic acid

• Cell membrane

Answer explanation

Answer: B. Lipid A is a lipid component of an endotoxin held responsible for the toxicity of gram-negative bacteria. It is the innermost of the three regions of the lipopolysaccharide (LPS), also called endotoxin molecule, and its hydrophobic nature allows it to anchor the LPS to the outer membrane.

 

Reference: Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

Which term describes a bacterial species that alter its shape in response to varying environmental conditions?

• Amorphous

• Unusual

• Pleiomorphic

• Stalked

Answer explanation

Answer: C. Pleomorphism refers to the ability of an organism to alter its morphology and reproductive and other metabolic behavior in response to environmental changes.

 

Reference: Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

McLaughlin, R. W., Vali, H., Lau, P. C. K., Palfree, R. G. E., De Ciccio, A., Sirois, M., Ahmad, D., Villemur, R., Desrosiers, M., & Chan, E. C. S. (2002). Are there naturally occurring pleomorphic bacteria in the blood of healthy humans? Journal of Clinical Microbiology, 40(12), 4771–4775. https://doi.org/10.1128/jcm.40.12.4771-4775.2002

Which of the following staining methods is NOT used to observe bacterial capsules?

• Schaeffer Fulton method

• Anthony's method

• Maneval's staining method

• Negative staining

Answer explanation

Answer: A. The Schaeffer–Fulton stain is a technique designed to isolate endospores by staining any present endospores green, and any other bacterial bodies red. The primary stain is malachite green, and the counterstain is safranin, which dyes any other bacterial bodies red.

 

Reference: Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

https://microbiologynotes.org/endospore-staining-and-capsule-staining-of-the-bacteria/

https://microbiologie-clinique.com/endospore-staining-malachite-green.html