Molecular Basis of Bacterial Infections Evelien Floor
Bacterial pathogenesis at the
mucosal surface
Stomach – Helicobacter pylori
H. pylori is a well-known bacterial species and colonizes the stomach. Half of the world is colonized
by this bacterium. It plays a role in gastritis and peptic ulcer disease. They form small colonies and
grow under complicated nonstandard lab conditions.
Challenges for H. pylori are:
Low pH
Mucus layer
Peristalsis/fluid flow
H. pylori penetrates the mucus layer with the use of its flagella because the pH is a bit higher in
mucus than in the lumen: chemotaxis. If it stays in the lumen it will eventually die because of the low
pH. Once in the mucus it starts secretion of urease to increase the pH. Urease converts urea into
ammonia and CO2. Ammonia has a very high pH. The mucus of the stomach with low pH is very
viscous but at higher pH it becomes more fluid. This is beneficial for its movement through mucus.
Afterwards it adheres to the mucus layer with SabA, an adhesin that binds sialic acid on mucins. Then
it attaches to the enterocytes using its T4SS and injects effectors that cause cell damage and
inflammation. It also secretes damaging enzymes.
For tumor formation CagA is needed to activate the EGFR. Not all the H. pylori strains contain this
protein. It is not known why H. pylori infects humans and can even kill them because there is no
benefit in it for the bacteria.
Colon – Salmonella enteritidis & Campylobacter jejuni
Both S. enteritidis and C. jejuni infections originate from eating infected animal meat (chicken, cow).
These bacteria are highly infectious, people can be sick for 1-2 weeks with a lot of (bloody) diarrhea.
Salmonella causes a lot of deaths per year. Campylobacter is able to cause Guillain-Barré syndrome.
Challenges for S. enteritidis and C. jejuni are:
Low pH
Peristalsis/fluid flow
o However, they can use this to migrate
Mucus layer
Resident microbiota
Salmonella consists of a lot of fimbriae to bind sugars in mucus. Salmonella is also able to degrade
mucus. Both Salmonella and Campylobacter use the mucus layer for adhesion via adhesins.
Campylobacter uses the mucus layer for motility. The biggest challenge for those bacteria is
1
Bacterial pathogenesis at the
mucosal surface
Stomach – Helicobacter pylori
H. pylori is a well-known bacterial species and colonizes the stomach. Half of the world is colonized
by this bacterium. It plays a role in gastritis and peptic ulcer disease. They form small colonies and
grow under complicated nonstandard lab conditions.
Challenges for H. pylori are:
Low pH
Mucus layer
Peristalsis/fluid flow
H. pylori penetrates the mucus layer with the use of its flagella because the pH is a bit higher in
mucus than in the lumen: chemotaxis. If it stays in the lumen it will eventually die because of the low
pH. Once in the mucus it starts secretion of urease to increase the pH. Urease converts urea into
ammonia and CO2. Ammonia has a very high pH. The mucus of the stomach with low pH is very
viscous but at higher pH it becomes more fluid. This is beneficial for its movement through mucus.
Afterwards it adheres to the mucus layer with SabA, an adhesin that binds sialic acid on mucins. Then
it attaches to the enterocytes using its T4SS and injects effectors that cause cell damage and
inflammation. It also secretes damaging enzymes.
For tumor formation CagA is needed to activate the EGFR. Not all the H. pylori strains contain this
protein. It is not known why H. pylori infects humans and can even kill them because there is no
benefit in it for the bacteria.
Colon – Salmonella enteritidis & Campylobacter jejuni
Both S. enteritidis and C. jejuni infections originate from eating infected animal meat (chicken, cow).
These bacteria are highly infectious, people can be sick for 1-2 weeks with a lot of (bloody) diarrhea.
Salmonella causes a lot of deaths per year. Campylobacter is able to cause Guillain-Barré syndrome.
Challenges for S. enteritidis and C. jejuni are:
Low pH
Peristalsis/fluid flow
o However, they can use this to migrate
Mucus layer
Resident microbiota
Salmonella consists of a lot of fimbriae to bind sugars in mucus. Salmonella is also able to degrade
mucus. Both Salmonella and Campylobacter use the mucus layer for adhesion via adhesins.
Campylobacter uses the mucus layer for motility. The biggest challenge for those bacteria is
1
