Gene Xpert

The Gene Xpert is a new test for tuberculosis. It can find out if a person is infected with TB, and also if the TB bacterium of the person has resistance to one of the common TB drugs, rifampicin.

How it works

The Gene Xpert is a machine that can detect mycobacterium tuberculosis in a sample of sputum. A person suspected of having TB needs to give a sputum sample, which the health care worker than places in a small tube. From the tube, the sample is fed into the machine, and then biochemical reactions are started to see if the sample contains the TB bacterium. The machine looks for the DNA specific to the TB bacterium. If there are TB bacteria in the sample, the machine will detect their DNA and automatically multiply it. This technique is called PCR (polymerase chain reaction), and allows the machine to also look at the structure of the genes. This is important to detect if a TB bacterium has developed resistance to drugs. The DNA of the TB bacterium is, in a way, like a long string of different colours. If one or more of the colours change (if there is a mutation in the DNA), then the bacterium can become resistant to certain TB drugs. The Gene Xpert can test for resistance to one of the most common TB drugs, rifampicin. This means that it can tell us two things: first, whether or not a person has TB, and second, whether or not the TB that the person has can be treated with rifampicin. The test is very quick and only takes about two hours – much faster than the other TB tests, which usually take at least a few days.

 

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