Lecture notes
Neisseria
- Module
- Mechanisms of pathology
- Institution
- Aston University, Birmingham (Aston)
in depth immunology notes
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Neissseria.Phylogenetic overview of bacteria.
Phylogenetically (their classification), is that these organisms, based on their 16s
ribosomal subunit sequencing.
There is a whole range of organisms, but there is a characteristic group called the
proteobacteria.
If we look within the proteobacteria, which are all gram-negative organisms that live
in a whole host of places, including the soil, and conduct useful functions such as
fixing nitrogen.
But the Neisseria sit within the beta proteobacteria.
Neisseriales.
Kingella can cause infections that are deep-seated of the bone and the joints.
Eikenella can cause a series of infections associated with bites.
These organisms were named after the people that discovered them.
They are pleiomorphic- so they have multiple shapes.
They are gram negative organisms.
They colonize the oropharynx and the upper respiratory tract; this means the sort of
infections you can get from these come from a bite.
This is important for front line NHS workers because bites can be occupational
hazard.
Neisseria.
There are multiple species, but two important species are important, and these are:
Neisseria gonorrheae and nisseria meningitidis.
These are important human pathogens.
Neissseria- characteristics.
Neisseria have a characteristic diplococcus shape.
They are small organisms.
They are fastidious, which means that they are difficult to please.
Often when we are culturing them, we need to provide to them a series of growth
factors, such as amino acids, purines, pyrimidines etc.
But we also need to give them a raised level of carbon dioxide in their culture
environment, because they are capnophilic.
They have certain biochemical characteristics as well and this can help in the
identification of the organism.
The gonococcus and meningococcus are both oxidase positive, and they are also
both catalase positive.
Catalase is an enzyme that catabolizes hydrogen peroxide, to break it down to
oxygen and water.
We can put a 3% hydrogen peroxide solution onto a plate containing colonies from
these different organisms.
If there is a lot of catalase activity, there is a lot of oxygen bubbles coming out from
the breakdown of the hydrogen peroxide.
, For the gonococcus, we usually see a strong positive catalase test whereas for the
meningococcus the catalase response varies.
We can also look at the biochemistry of organisms by looking at which sugars they
can use as a carbon and energy source.
We are looking to see if they can metabolize different sugars to generate acids.
Glucose is metabolized effectively by both the meningococcus and the gonococcus.
However, maltose is not, it is only metabolized by the meningococcus and not the
gonococcus.
This test gives us an opportunity to speciate the organism.
Telling the difference between the meningococcus and the gonococcus.
Neisseria-gram negative envelope.
Structure of Neisseria:
These organisms are non-motile.
They are gram negative and have a typical gram-negative envelope. They have an
internal plasma membrane, they have a periplasmic space within which the
peptidoglycan layer sits. And they have an outer membrane in which the
lipopolysaccharides sit, but in the case of Neisseria this is a reduced size. There is a
series of membrane proteins in the plasma membrane and the outer membrane.
There are lipoproteins and there are also these long proteinaceous structures called
pili and they are important functionally for the biology of this organism.
Pilli.
Long proteinaceous strands coming of the surface of the diplococcus.
These are important because they mediate attachment to host cells.
An organism can stick to a host cell, set up a focus of infection, it does this by using
the long strand.
And at the end of this proteinaceous strand is a protein subunit called Pil C.
This binds to a protein on the host cell called CD46.
Structure of pili:
They are very long proteinaceous structures, and they have a whole series of
subunits within them.
They have a terminal 5 prime N terminus domain called the PIL C. This is constant so
it does not change much.
Then we have a whole series of repeating units, which are collectively called PIL E.
The E means expressed.
So these are a whole series of expressed units, but there is a lot of variation here
because we find that within the truncated subunit, we do not get expression of a
whole long protein, and this allows the organism to turn the expression of Pili on and
off, this is something called phase variation.
By using one of the whole series of different subunits it is possible to get massive
variation here.
And the recombination of different gene segments allows for diversity.
This is important because diversity provides a way of hiding from the immune
system.
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