what is a capsule
a capsule is a thick protective layer made of polysaccharides around a bacteria
Bacillus anthracis capsule – composition and importance
Capsule made of D-glutamic acid (polypeptide)
Encapsulated strains cause anthrax
Capsule prevents phagocytosis and enhances virulence
the over all negative charge = inhibits phagocytosis
Streptococcus pyogenes
- M protein capsule (100 M serotypes), anti-phagocytic, Virulence factor
-causes (strep)Pharyngitis,(skin irritation) impetigo,
erysipelas, cellulitis,
necrotizing fasciitis, toxic
shock syndrome
-25% death rate
group A infects
Streptococcus pneumoniae
-Polysaccharide capsule
-Cells lacking capsule do not
cause pneumonia
capsule advantage of microbes
-protection against harsh conditions
-protection from innate system long enough to cause disease
-k antigen and o antigen cause alot of varieties making it hard for the antibodies to recognize
advantges to the microb that has casple
-helps it attach to surfaces
-allows to escape the immune system
-protect against harsh eniovorments
Capsule
A layer firmly attached to the bacterial cell, often linked to lipids in the membrane.
Mostly made of carbohydrates, though some capsules are made of proteins.
Composed of long chains of repeating units, which can be all the same (homopolymer) or different (heteropolymer).
Structures vary: they can be straight or branched, giving bacteria lots of diversity.
K antigen: the capsule type in E. coli; there are 84 different types.
Group B streptococcus (Streptococcus agalactiae)
an opportunistic gram-positive pathogen
can a dead cell with capsule give capsule to noninfectious cell?
genetic material can be transferred to make non-virulent bacteria virulent.
capsules are classified into 4 groups(taxonomy)
there are 80 distinct types of capsular polysaccrides
-Groups 1 & 4: Made using the Wzy-dependent pathway.
-Groups 2 & 3: Made using the ABC transporter pathway.
OPX (Outer membrane Polysaccharide Export protein):
Forms a channel in the outer membrane so the capsule can exit the cell.
PCP (Polysaccharide Co-polymerase):
Helps transport and coordinate the polysaccharide chain across the periplasm to the OPX channel.
OPX/PCP
Come together to form a fluid-filled channel
Also an entry port near inner membrane
ABC transporter
ABC transporters help move capsule materials out of the cell.
They have 4 key parts:
2 Transmembrane Domains (TMDs): form a channel through the inner membrane.
2 Nucleotide-Binding Domains (NBDs): use ATP for energy to push materials through the channel.
The glycolipid (capsule building block) is passed from the ABC transporter to the PCP-OPX complex, which moves it across the periplasm and outer membrane to the outside of the cell.
In short:
ATP → ABC transporter → PCP & OPX → capsule exits the cell.
