MIB HC 1 – What is a pathogen?
What is a pathogen?
A biological agent that causes disease or illness to its host
- Viruses
- Bacteria
- Protozoa
- Yeast/fungi
- Worms
Pathogens:
Normal microflora Real pathogens
- Endogenous - Exogenous
- Beneficial for host? - pathogenic for host?
Normal microflora:
- Bacteria
- Protozoa
- Bacterial viruses
Gut microflora
- More than 500 species, mainly:
• Firmicutes → Clostridium species
• Bacteroidites → Bacteroides fragilis
Bacteroides thetaiotaomicron
- Gnotobiotic animals (germ-free):
• Worden gebruikt om gut microflora te onderzoeken
• Need 30% more calories
• Less vascularisation and poor development villi
• Underdeveloped mucosal immune response
Gut anaerobes (Bacteroides thetaiotaomicron) degrade and ferment indigestible plant material
- Release of small simplified carbohydrates (butyric acid)
- Zonder kunnen we geen planten verteren
- Release amino acids die plantmateriaal verteren
So B. thetaiotaomicron produces enzymes on the surface → breakdown plantmaterial into simple
sugars and carbohydrates (like butyric acid) → these are adsorbed by the gut
,Gut microflora induce immune response, including production of antimicrobial peptides
→ muramyl dipeptides
are released from
peptidoglycan layer →
stimulate immune
response
Cells of the gut produce low amount of antimicrobial peptides
Microflora produces bacterial compounds that stimulate immune response
→ stimulate TLR production (mainly by PAMPs) → stimulate immune response
Diseases by normal microflora
1. Normal microflora at the wrong place
2. Abnormalities in host defence
, Normal microflora at the wrong place
- Damage to the epithelium (B.fragilis)
• Damage to colon epithelium (spontaneous, after surgery) results in the infiltration of
gut microflora in peritoneum → coinfection E.coli and B.fragilis (= synergistic) which
results in abscess formation, high morbidity and mortality
- New site for normal microflora (E.coli)
• Urinary tract infections: E.coli
• Can result in bladder infections (cystitis) and kidney infections (pyelonephritis)
• Mainly in women → close proximity urethra and anus
- Foreign bodies (surgical implants) (Staph. epidermidis)
- Wrong host (E.coli O157)
• Different mammals have similar composition of gut flora, however, with strain-
specific bacteria
• Example outbreak of E.coli O157:H7
- Apple juice infected by E.coli from deer poop (molecular strain identification, PFGE)
- Deer don’t get ill from this strain, but humans will
- E.coli O157:H7
> O = LPS
> H = Flagella
> K = Capsule
• Example wrong host/wrong place
- Humans sometimes get infected when bitten by dogs/cats
- 5-10% becomes infected
- Capnocytophaga canimorsus belongs to the normal oral flora of dogs and cats
- Infection with C.canimorsus → sepsis
What is a pathogen?
A biological agent that causes disease or illness to its host
- Viruses
- Bacteria
- Protozoa
- Yeast/fungi
- Worms
Pathogens:
Normal microflora Real pathogens
- Endogenous - Exogenous
- Beneficial for host? - pathogenic for host?
Normal microflora:
- Bacteria
- Protozoa
- Bacterial viruses
Gut microflora
- More than 500 species, mainly:
• Firmicutes → Clostridium species
• Bacteroidites → Bacteroides fragilis
Bacteroides thetaiotaomicron
- Gnotobiotic animals (germ-free):
• Worden gebruikt om gut microflora te onderzoeken
• Need 30% more calories
• Less vascularisation and poor development villi
• Underdeveloped mucosal immune response
Gut anaerobes (Bacteroides thetaiotaomicron) degrade and ferment indigestible plant material
- Release of small simplified carbohydrates (butyric acid)
- Zonder kunnen we geen planten verteren
- Release amino acids die plantmateriaal verteren
So B. thetaiotaomicron produces enzymes on the surface → breakdown plantmaterial into simple
sugars and carbohydrates (like butyric acid) → these are adsorbed by the gut
,Gut microflora induce immune response, including production of antimicrobial peptides
→ muramyl dipeptides
are released from
peptidoglycan layer →
stimulate immune
response
Cells of the gut produce low amount of antimicrobial peptides
Microflora produces bacterial compounds that stimulate immune response
→ stimulate TLR production (mainly by PAMPs) → stimulate immune response
Diseases by normal microflora
1. Normal microflora at the wrong place
2. Abnormalities in host defence
, Normal microflora at the wrong place
- Damage to the epithelium (B.fragilis)
• Damage to colon epithelium (spontaneous, after surgery) results in the infiltration of
gut microflora in peritoneum → coinfection E.coli and B.fragilis (= synergistic) which
results in abscess formation, high morbidity and mortality
- New site for normal microflora (E.coli)
• Urinary tract infections: E.coli
• Can result in bladder infections (cystitis) and kidney infections (pyelonephritis)
• Mainly in women → close proximity urethra and anus
- Foreign bodies (surgical implants) (Staph. epidermidis)
- Wrong host (E.coli O157)
• Different mammals have similar composition of gut flora, however, with strain-
specific bacteria
• Example outbreak of E.coli O157:H7
- Apple juice infected by E.coli from deer poop (molecular strain identification, PFGE)
- Deer don’t get ill from this strain, but humans will
- E.coli O157:H7
> O = LPS
> H = Flagella
> K = Capsule
• Example wrong host/wrong place
- Humans sometimes get infected when bitten by dogs/cats
- 5-10% becomes infected
- Capnocytophaga canimorsus belongs to the normal oral flora of dogs and cats
- Infection with C.canimorsus → sepsis
