Survival of the fattest: TB bacterium uses fat to survive and spread
1 April 2008
Scientists have discovered droplets of fat in the bacterium that causes tuberculosis (TB) and that this fat content may help Mycobacterium tuberculosis to survive when it spreads to new people. It is also thought the fat helps increase the bacterium’s resistance to drugs.
The scientists say the finding challenges the established view that the TB bacteria coughed up by infected individuals multiply rapidly.
The Leicester team discovered that, unlike TB bacteria growing in test tubes, many of the bacteria found in sputum are loaded with fat droplets. With the help of colleagues at St Georges, University of London, they went on to show that these ‘fat bacteria’ are in a non-growing state, a condition in which they are more likely to survive the process of passing from one person to another. The research is published in the journal Public Library of Science Medicine.
This image shows a Mycobacterium tuberculosis bacterium, laden with fat droplets, found in a patient’s sputum sample. The cell is around one hundred thousandth of a millimetre in length. It is difficult obtain clear images in sputum samples at this magnification so the image has been enhanced to give a stronger impression of the cell structure.
Mike Barer, Professor of Clinical Microbiology at the University of Leicester, describes the moment he saw this cell while working in the MRC laboratory in The Gambia as a ‘real eureka moment.’ He said:
"We think the droplets, stained red in this image, signify the bacterium's readiness for transmission and suspect the higher the proportion of droplet-laden cells in the sputum sample, the slower the patient will respond to treatment.’’
“We examined TB in sputum samples from infected patients to get a snapshot of the disease at the point of its transmission to a new person and compared the characteristics of these bacteria with those of TB growing in the laboratory.”
The research revealed the presence of fat deposits and related gene expression patterns which the scientists believe may help the TB bacterium to survive during transmission and establish a new infection in another person.
The study was funded by the Medical Research Council, the Wellcome Trust, the British Lung Foundation and the Henry Smith Charity.
Original research paper: Cytological and transcript analyses reveal fat and lazy persister-like bacilli in tuberculous sputum is published in PLoS Medicine.
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