Investigating the cause of the symptoms
To find the pathogen in a human, a A small amount of tissue, faeces, or body fluids removed from an individual for diagnostic testing. must be taken from the individual that is ill. The sample is a small amount of tissue or fluid. More diagnostic tests are carried out on the sample.
Identifying cells
A special kind of microscope slide with a grid marked on it is used to count cells in the sample. The cells which are counted could be pathogens or they could be white blood cells. When a person is infected their white blood cell count increases.
There are also different dyes which may be used to stain the pathogens. A procedure for staining bacteria to distinguish between those that are Gram positive and those that are Gram negative. is used for bacteria. Not all bacteria are stained the same colour with Gram stain - Gram positive bacteria stain purple while Gram negative bacteria do not absorb the dye.
Pathogens can be grown on agar in petri dishes in carefully controlled conditions. This increases the number of cells so that different diagnostic tests can be used for identification. In one type of test the culture conditions are changed to favour the growth of a specific strain of bacteria and to kill others. An example of this would be to add a certain antibiotic to the agar plate. If the pathogen can grow in these modified conditions then it is identified as belonging to the known strain.
Genome analysis
Techniques such as genetic testing and genetic engineering that are based on our understanding of the genome. can be used to help identify a pathogen by analysing the A different version of a gene. They are small changes in the DNA created by mutations. Most changes do not affect the way the gene is expressed. in its DNA.
A short section of single-stranded DNA, which has a sequence of bases which pairs up with the bases in a particular genetic variant.The probe binds to that variant in the DNA sample. are short lengths of single-stranded DNA which will pair up with the bases in a particular genetic variant of a known pathogen. For example, a strand whose base sequence is AATTCGCGGTA will attach to a section of pathogen DNA whose sequence is TTAAGCGCCAT. They may be attached to a molecule of a When a chemical absorbs ultraviolet light and releases it as visible light. substance, which can appear to glow in UV light. This means that scientists can test for diseased tissue much more quickly than with traditional methods.
Using A technique that works out the complete sequence of bases in an individual's DNA. of the pathogen in the sample could also help identify it, for example when identifying rare illnesses.
Isolation and re-infection
In plants, pathogens can be When a pathogen has been separated from disease tissue and from other microbes or cells so it is pure. and then used to re-infect a healthy plant. If the same symptoms appear, then that is evidence that the disease is caused by that pathogen.