Back to Bacteria
Bacteroides fragilis
Bacteroides fragilis
Gram Negativebacilli
Description
B. fragilis is an obligate anaerobic gram-negative bacterium that is a normal member of the human gut microbiome. It plays important roles in polysaccharide breakdown and immune system development but can cause infections if it escapes the gut.
Membrane Composition
Key Properties
Peptidoglycan:2-7 nm (thin)
Lipopolysaccharide:Present
Teichoic Acid:Absent
Outer Membrane:Present
Membrane Components
- •Inner membrane
- •Thin peptidoglycan
- •Outer membrane with modified LPS
- •Capsular polysaccharides
Understanding Gram Classification
Gram-negative bacteria do not retain the crystal violet stain due to their thin peptidoglycan layer (2-7 nm) and outer membrane structure. They appear pink/red after counterstaining with safranin.
The cell envelope has a complex structure: an inner membrane, a thin peptidoglycan layer in the periplasmic space, and an outer membrane containing lipopolysaccharides (LPS). This outer membrane provides extra protection against antibiotics and immune responses.