Are you a disease detective?
When we eat food which contains bad bacteria (foodborne bacteria) it can make us very ill. One symptom is diarrhoea.
By analysing faeces (poo) from infected people, we can find out which species of bacteria is present. This information can be used to provide the correct treatment or find the food source to stop it happening again.
Diagnostic labs use lots of techniques and one method uses a mass spectrometer to identify bacteria. Here we show how we can use this technology to identify foodborne bacteria.
Step 1 - Grow bacteria
In laboratories, scientists spread a tiny amount of poo on an agar plate which provides everything a bacteria needs for growth. Antibiotics can be used to stop other bacteria growing so we only “see” the bad bacteria.
One bacterium can duplicate itself in as little as 20 minutes so if a bad bacteria is present, after 24-48 h it will have multiplied to over a trillion bacteria.
This forms a little lump on the plate called a colony which can be analysed.
Step 2 - Mashup
The bacteria are scooped off the agar plate and carefully added to tube which contains a mixture of strong chemicals, usually acids and organic solvents.
The chemicals kill the harmful bacteria and break the bacteria into bits which releases proteins. Proteins are compounds that are found in all living things.
The tubes are mixed vigorously using a device called a vortex mixer.
Each bacteria is made of different proteins. So the protein mix is specific to each bacteria.
Step 3 - Put on a plate
A small drop of the liquid protein mix is added to a metal plate.
The sample is allowed to dry. As there is volatile organic solvent present this happens quickly.
A drop of liquid containing a saturated matrix in organic solvent is added.
The organic solvent evaporates to leave proteins coated in matrix “crystals”.
The matrix crystals prevent the proteins from exploding in the next step.
The plate is now ready to go into the mass spectrometer.
... inside the spectrometer
Firing
A powerful laser inside the machine is fired at the plate.
... inside the spectrometer
Firing
A powerful laser inside the machine is fired at the plate.
... inside the spectrometer
The matrix absorbs energy from the laser and passes on the energy to the proteins. The energised proteins then move from a solid to a gas (desorption).
The charged (ionised) matrix transfers a proton to the proteins.
Ionised proteins are then accelerated down a time of flight tube for mass analysis.
... inside the spectrometer
The matrix absorbs energy from the laser and passes on the energy to the proteins. The energised proteins then move from a solid to a gas (desorption).
The charged (ionised) matrix transfers a proton to the proteins.
Ionised proteins are then accelerated down a time of flight tube for mass analysis.
... inside the spectrometer
Particles fly
As the ions enter the flight tube the lighter ions will travel faster than the heavier ions to the detector.
Flight tubes are normally 1-2 metres long.
... inside the spectrometer
Particles fly
As the ions enter the flight tube the lighter ions will travel faster than the heavier ions to the detector.
Flight tubes are normally 1-2 metres long.
... inside the spectrometer
Detector
As the ions enter the flight tube the lighter ions will travel faster than the heavier ions to the detector.
Flight tubes are normally 1-2 metres long.
... inside the spectrometer
Detector
As the ions enter the flight tube the lighter ions will travel faster than the heavier ions to the detector.
Flight tubes are normally 1-2 metres long.
Step 5 - Record the data
The time of flight of each ion is recorded and the data is presented as a mass spectra.
Because each bacterial type gives a different mix of proteins, the generated spectra is also unique and is like a bacterial fingerprint or barcode.
Diagnostic labs in hospitals have databases of spectra for thousands of bacteria which they use to identify bacteria in all sorts of samples.
Pathogen info
