Overview
This lecture reviews atypical bacterial cell walls, focusing on wall-less bacteria and acid-fast bacteria, highlighting their structure and clinical significance.
Wall-less Bacteria (Mycoplasma)
- Some bacteria lack cell walls; the most notable genus is Mycoplasma.
- Mycoplasma are the smallest bacteria capable of reproduction outside host cells.
- They survive without a cell wall due to their small size and sterols in their plasma membrane.
- Their sterols are related to cholesterol, providing membrane stability similar to that in animal cells.
Acid-fast Bacteria
- Acid-fast bacteria have a unique waxy cell wall containing mycolic acid, making up to 60% of the wall.
- This waxy layer is hydrophobic and prevents Gram stain uptake.
- If the mycolic acid is removed, acid-fast bacteria would stain Gram positive.
- Main genera: Mycobacterium (notably Mycobacterium tuberculosis and Mycobacterium leprae) and rarely, pathogenic Nocardia.
- Mycobacterium tuberculosis causes tuberculosis; Mycobacterium leprae causes leprosy (Hansen’s disease).
Key Terms & Definitions
- Atypical cell wall — a bacterial cell wall structure differing from typical Gram-positive or Gram-negative walls.
- Wall-less bacteria — bacteria lacking a cell wall, such as Mycoplasma.
- Sterols — lipid molecules in cell membranes providing structural stability.
- Acid-fast bacteria — bacteria with a waxy mycolic acid layer in their cell wall, resistant to Gram staining.
- Mycolic acid — a hydrophobic, waxy substance forming a protective outer layer in acid-fast bacteria.
Action Items / Next Steps
- Review differences between typical and atypical bacterial cell walls.
- Read about Mycoplasma, Mycobacterium tuberculosis, and Mycobacterium leprae for clinical context.