Could some tuberculosis bacteria have evolved so that they have actually become dependent on one of the key drugs used in TB treatment? A case study (1) in China raises this disturbing possibility. Bacteria isolated from a TB patient in whom treatment had failed were found to grow poorly without the antibiotic rifampicin and to grow better in its presence. The authors of the report say that this case demonstrates the importance of drug susceptibility testing, and that doctors should be prepared to remove rifampicin from a patient’s treatment regimen if resistance to the drug has been demonstrated.
Another TB research article published in recent days reports disappointing findings. One of the reasons why it is so difficult to control this disease is the ability of the bacterium Mycobacterium tuberculosis to lie dormant for many years, then suddenly emerge to cause serious disease. It was proposed a few months ago by Swedish researchers that M. tb. might have the ability to turn into dormant, highly-resistant spores. If true, this would provide promising new avenues of research in the fight against TB. However, a new study (2) by US scientists has found no evidence that M. tb can actually form spores.
Working with the organism Mycobacterium marinum, often used in TB research, the researchers used genomic techniques to demonstrate that mycobacteria are unlikely to be able to form spores. They were also unable to detect the presence of spores by light microscopy or by testing for heat-resistant, colony-forming units in aged cultures of M. marinum. And they failed to recover heat-resistant colony-forming units from frogs chronically infected with M. marinum. So it may be back to the drawing board to find an explanation for TB dormancy.
1. Zhong M, Zhang X, Wang Y, Zhang C, Chen G, Hu P, Li M, Zhu B, Zhang W, Zhang Y (2010). An interesting case of rifampicin-dependent/-enhanced multidrug-resistant tuberculosis. Int J Tuberc Lung Dis; 14(1):40-44. Abstract on PubMed. (Full paper not open access.)
2. Traaga BA Driks A, Stragier P, Bitter W, Broussard G, Hatfull G, Chu F, Adams KN, Ramakrishnan L, Losick R (2009). Do mycobacteria produce endospores? Proc Natl Acad Sci USA; Abstract published online before print (Full paper not open access.) A summary is available on EurekAlert.