Lecture notes
gram negative facultative anaerobes
- Module
- Mechanisms of pathology
- Institution
- Aston University, Birmingham (Aston)
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Gram negative facultative anaerobes.Enterobacteriaceae
Traits of Enterobacteriaceae:
1. Gram negative straight rods, which are sometimes called bacilli. They are very
straight rods.
2. They are known as facultative anaerobes, this means that they normally live with the
presence of oxygen, so they normally breath oxygen in. however, given the chance, if
oxygen does get depleted they can change how they respire. They can respire
through different mechanisms to stay alive.
3. Non-sporulating- gram positive bacilli release spores, these spores can go on to
infect people. This type of family do not produce spores.
4. Catalase positive- all of the Enterobacteriaceae family are catalase positive, which
means that they convert the hydrogen peroxidase to oxygen. In the laboratory we
will take a small colony of this bacteria that we have grown, we will place it on a
slide, add 3% hydrogen peroxide and if it bubbles this means that it is catalase
positive.
5. Oxidase negative- oxidase negative is a test that we do in the laboratory. It is to test
for the presence of cytochrome c chain. The enzyme oxidase is part of that, by
having a negative result it means that they lack this type of chain.
6. Ferment sugars to acid- this type of bacterial family infect a lot of food types and
cause food poisoning. Normally we send a batch of food to a food testing lab and
they will test for the presence of salmonella or E.coli using a type of agar plate. If
they test positive, the food from that batch will be recalled, because they have found
a type of bacteria in the food.
Some organisms might show these traits but may not technically be part of the
Enterobacteriaceae family.
Some genetic testing has been done on bacteria and we are changing our views on
the families that they should be placed in.
A study was done, and they take different parts of genetic info from bacteria using
CISIS’S.
Family has been split based on their ancestral history.
Salmonella focus.
Salmonella genus.
The salmonella is part of the Enterobacteriaceae family.
The salmonella genes is split into S.bongori and S.enterica, we normally split them
there due to the origins.
The bongori is normally found in reptile strains and the enterica is normally found in
mammals.
In the S.enteria subspecies we have over 2400 serotypes.
The subspecies enterica also has two different subtypes. These are nontyphoidal and
typhoidal.
The Typhoidal serotype causes “typhi fever”. This is dangerous and can lead to
systemic failure.
, The nontyphoidal serotype causes gastroenteritis. This is common food poisoning
that we see.
Salmonella genus characteristics.
Salmonella genus characteristics:
They are the same as mentioned for all Enterobacteriaceae.
They are gram negative bacilli.
They are facultative anaerobes meaning that they can use oxygen or they can breath
without the presence of oxygen.
They are catalase positive which means that they produce catalase enzyme that
changes the hydrogen peroxide to the oxygen.
They are also oxidase negative which means they lack cytochrome c.
Salmonella has flagella, and this is how it stays motile. This is different for the
salmonella genus compared to other families of Enterobacteriaceae.
Salmonella do not produce lactose so when placed in a lactose environment they do
not produce it.
They are indole negative, this means that they do not have trepsonin which changes
in the tripan to indole.
Serotypes: Kauffman-white classification.
The flagella is used for the motile and it helps the salmonella to move around.
However it is also used to discuss our serotypes.
We use the Kauffman-white classification scheme here, this works for salmonella
and E.coli as well.
Most Kauffman-white schemes will display an O antigen and a H antigen.
The O antigen is part of our cell wall. The O comes from the oligosaccharide
sequences that make up the cell membrane. These antigens are heat stable and
alcohol resistant as well.
Each different type of O antigen will be classified as something different.
On top of this for the serotype classification we have the H antigen, which is the
flagella these are split into a letter and a number sometimes. Sometimes they don’t
have a letter and sometimes they do not have a number and this just depends on
where the genetic reading for the flagella comes from.
For example, it could be from the inner part and the end part, this type of
classification is how we name our serotypes for salmonella and E.coli species and
other bacterial species as well that have flagella.
This is an old classification system to be using.
It is still valid and we still use it in science today, however with the current discussion
of changing how we look at bacteria instead of using their phenotypes and
characteristics to place them into families, we are using genetics.
This type of classification may no longer be used.
Salmonella infection.
All salmonella are opportunistic pathogens. They hang around in the gut and they
will not cause you any harm until they decide that its time to cause harm.
The way salmonella gets into our bodies is because they live within animal species,
so we can have direct contact with these animals in terms of : the chicken will lay the
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