CURRENT AND EMERGING PATHOGENS.
– To highlight current & emerging foodborne pathogens using Salmonella
Campylobacter and E. coli O157 as examples.
– Following this lecture you should be able to:
• Relate the microbiology, epidemiology and pathogenicity of
Salmonella, Campylobacter & E. coli O157.
• Define the symptoms presented following infection with Salm. Camp.
and E. coli.
• Describe the routes of transmission of Salm. Camp. and E. coli and
how they become associated with food.
SALMONELLA.
• Theobald Smith
– 1885
• Salmonella as a human pathogen
– Germany 1881
• Binomial nomenclature
– Kauffmann & White Scheme 1934
• Serotyping: O, H, Vi surface antigens
(O- LPS, H- Flagella, Vi- Capsular antigen)
Salmonella- Theobald smith first isolated this.
Him and his colleague were looking at an organism that causes disease in pigs.
The first recorded incidence of salmonella in humans was in Germany. This is where a cow
came into the streets and died, and people had slaughtered it and eaten it. However, the
cow had salmonella infection which is why it died and this had then been passed onto the
people.
Zoonotic infection- transfer of infection from an animal to human.
Salmonella- binomial nomenclature: uses the serotyping- the coffin and white scheme, this
is how we identify different strains of organisms. This one is relating to the serotyping, so
the serological response that we see with the antigens on the bacteria's outer surface. The 0
antigen is the LPS – the lipopolysaccharide. The H antigen is the flagella, and the VI is the
capsule antigen. Not all salmonella have capsules.
Based on the reaction that we see on the serotyping; this is how salmonella is given its
name.
SALMONELLA TOXONOMY
• Currently accepted taxonomical position
– 2 species
• Salmonella enterica
– 6 subspecies
– Salmonella enterica subsp. enterica
, – Salmonella enterica subsp. salamae
– Salmonella enterica subsp. arizonae
– Salmonella enterica subsp. diarizonae
– Salmonella enterica subsp. hautenae
– Salmonella enterica subsp. Indica
• Salmonella bongori
Salmonella
We have genus and species.
In salmonella there is only 2 true species.
Genus- salmonella.
The species- enterica and bongori.
But the majority of the salmonella fits into the species enterica.
Then it gets classified even further into sub-species, so we have various different ones, there
are 6 of them.
We take it even further and this is where the serotyping information comes in.
We can say salmonella typhimurium. – all this tells you is that salmonella is the genus and
typhimurium is the serotype.
The reason that this is different- we are referring to the serotype- not italicized. Thousands
of strains of serovars of salmonella.
SALMONELLA
• Gram-negative
• Peritrichous flagella – highly motile
• Non-sporulating, facultatively anaerobic bacilli
• Temperature: 7 – 48°C (Mesophile)
– Optimum growth at 37°C
– pH 4 – 8 (Neutrophile)
– Optimum growth at pH 7
• Water activity - Aw >0.93
– water availability of the environment
Pure water Aw -1.0 Soy sauce Aw -0.80 Biscuits Aw >0.60 Honey Aw >0.60
Salmonella.
Gram negative
Peritrichous flagella- highly motile- peritrichous this means that the flagella are distributed
all across the surface of the organism this means that they can go in all different directions,
they can be very motile because of this, which means that they may be more invasive.
Non-sporulating- does not form spores.
Facultatively anaerobic bacilli- this means that it can switch between the two. This means
that it can grow in an environment with oxygen present, but if there is oxygen absent it can
switch its metabolism and grow in that environment in a different environmental pathway.
Salmonella is defined as a mesophile- in the middle- and their optimum temp is 37 degrees.
Neutrophile- the pH conditions in the environment they are in. it is a neutrophile, so it does
not like anything to extreme.
, This is important for food microbiology- we understand salmonellas' requirements and
characteristics and by understanding this we can establish how we can prevent salmonella
being in our food.
Temperature- if we heat something beyond its maximum temperature that it can grow,
where we can kill it off, we can eliminate salmonella as being a potential pathogen that we
can eat.
We can do the same thing with PH, food where we can adjust the PH, like pickled food or
things that are in vinegar. Or where things were PH has been altered, by doing this we will
know that we have eliminated certain organisms.
Water activity- AW- this is important requirement for the organism to grow it needs access
to water. Water activity is being able to measure the available water in an environment.
Avaliable water refers to if that water is accessible for the microorganism to utilize as part of
its metabolism.
Pure water has a water activity of 1, which is the maximum that you can have. This water is
freely available if microorganisms happen to be in contact with it. This water is available for
it to utilize in its metabolism.
Soy sauce, water activity has gone down because of the salts and sugars that are present
within it. These restrict the amount of water that is available for the microorganism to
utilize, because they essentially hold on to that water. So it is not as available for the
organism to utilize.
Biscuits/pasta- low water activity, do not go off, there are no microorganisms that can grow
where the water activity is below 6.
Honey- this is a wet product, the water is not available in this because of the different
sugars and different components that are in honey.
When talking about water activity, we are not talking about the organism we are talking
about the actual food matrix, the environment that it is in.
Need to understand these characteristics so that we know what to manipulate to eliminate
the organism and prevent infections.
Salmonella has a water activity of 0.93- high demand for water. If it is present in an
environment where the water activity is lower than that, such as biscuits, we will not get
that as a problem, as salmonella will not be able to survive or grow on those types of food
products.
Important so we can understand how to control these organisms
SALMONELLA PATHOGENICITY
• Gastroenteritis
– Headache, nausea, mild vomiting, profuse diarrhoea
• Incubation 8 – 48 hours (7d) usually 24 hours
• Infective dose 106 – 109 (<102) organisms
Dependent upon the host factors and the vehicle of delivery
• Infective dose can impact the incubation period, onset and severity of
symptoms.
• Bacteraemia
• Enteric fever - Typhoid: caused by Salmonella Typhi and Salmonella paratyphi
If you become infected with salmonella, you have a case of food-borne disease.
