Heat Signature Found for Tubercle Bacilli

A microcalorimeter has been used to detect the growth of Mycobacterium tuberculosis, the causative agent of tuberculosis, which proved to be faster than growing the bacteria in the laboratory and as fast as other more expensive methods.

Scientists at the Iberoamericana University (Mexico City, Mexico) evaluated the effectiveness of microcalorimetry in rapid detection of Mycobacterium species using an inexpensive isothermal microcalorimetry (IMC) instrument. In addition, they compared microcalorimetry with conventional monitoring techniques.

Microcalorimeters measure the heat given off during a chemical, physical or biological process, in this case when the bacteria grow. They convert this tiny temperature rise into an electrical signal, which can be amplified and recorded by a computer. This then produces a graphical footprint, which is unique to each species of bacteria.

Three different Mycobacteria species, M. tuberculosis, M. smegmatis, and M. avium grown in solid and liquid media were effectively detected with the TAM Air Waters (TA Instruments; New Castle, DE, USA) lower-cost IMC instrument. Multiple samples from the same person can be tested at the same time using the microcalorimeter it is also possible to test drug susceptibilities of the bacteria. This is done by measuring the growth of different samples in the presence of different antibiotics. If no growth is detected with one antibiotic, this drug can be used to fight the infection, which with the growing resistance of TB to antimicrobials, this is essential.

A further important feature of this method is that it uses readily available, cheap materials. Other fast TB detection methods often use consumables such as fluorescent or radioactive probes, meaning that every individual test comes at a significant cost. The relatively inexpensive microcalorimeters are commercially available, and it is estimated that a simple calorimeter can be built for around $1,000. Although this method works in a laboratory setting, this is not necessarily representative of the way it would work in outside world. Therefore, microcalorimeters have already been shipped to Tanzania in Africa and it is hoped to start a first validation of the approach in the field before the end of the year. The study was published on August 18, 2011, in the Journal of Applied Microbiology.

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Iberoamericana University
TA Instruments