Microbiology Quiz

Structures Outside the Bacterial Cell Wall

• Capsule is a gelatinous layer covering the bacterial cell wall, composed of polysaccharides or polypeptide.
• The capsule of Bacillus anthracis is composed of D-glutamic acid and is a determinant of virulence, preventing phagocytosis and enabling adherence and colonization.
• Capsules are used in vaccine production, such as the HiB vaccine, due to their antigenic character (K-antigen).
• Capsules also help bacteria resist desiccation and dryness.
• Flagella are long whip-like appendages composed of flagellin protein, responsible for bacterial motility and the H antigen.
• Pili, or fimbriae, are composed of pilin protein and serve as organs of attachment, as seen in E. coli, and as sex pilus for donor attachment.
• Klebsiella pneumoniae is an example of a bacterium with a distinctive capsule.
• The loss of capsule in bacteria can result in nonpathogenic strains.
• Capsules prevent phagocytosis by phagocytes and resist flushing.
• Flagella enable bacteria to move and navigate their environment.
• Pili are important for bacterial attachment and the transfer of genetic material.
• Dr. Rasha Mosbah, an Associate Professor of Microbiology & Immunology at the Faculty of Oral and Dental Medicine-ACU University, authored the content on structures outside the bacterial cell wall.