Evolution of Drug-Resistant Tuberculosis

By Emma Roache (VCE graduate 2006)

‘We’ve created this problem. Multi-drug resistance is a man made problem. By developing as many antibiotics as we have, we’ve essentially accelerated an evolutionary process…’ (Microbiologist- Mr. Barry Kreiswirth)
Due to human societal failures the evolution of drug-resistant strains of the tubercle bacillus has occurred all around the world. Until recently, this evolutionary change has largely posed a threat to the health and survival of the individual in whom inadequate therapy prompted the drug resistance.

Charles Darwin viewed evolution ‘as process to explain the multitudinous forms of life on our planet’. He also believed that there should be factors in the environment that create a selective advantage for the reproduction and survival of certain of those progeny (natural selection). The factor that is essential for the rising prevalence of drug-resistant tuberculoses around the globe is human intervention. The interplay between the two species; Mycobacterium tuberculosis and Home sapiens has evolutionarily created strains of tuberculosis resistant to modern medications.

The tubercle bacillus belongs to an unusual family of bacteria that presumably are related to have developed from the microbes that constitute the ‘living’ component of soil. They are believed to have first infected various animals and birds and then systematically introduced into human kind when humans domesticated cattle around 5000 B.C.

Certainly one of the most meaningful achievement of modern medicine has been the development Of therapy for this ancient scourge. Although it is a bacterium, the tuberculosis bacillus is highly resistant to the conventional antibiotics, such as penicillin or sulfa. In 1943-1944 a compound with substantial activity against tubercle bacillus was pressed rapidly into clinical use. Steptomycin, while most bacilli in the population where susceptible to the drug (they were killed rapidly by concentration of the medication), some mutant offspring were present that were resistant to the drug’s effects. When it was given alone, it killed the vulnerable population but left behind the resistant mutants. This is an example of Darwin’s selective process of ‘survival of the fittest’. Without competitions for the hosts’ tissues, these bacilli then became the dominant subspecies.

Fortunately two other medications were discovered shortly thereafter. Clinicians soon recognized that if all drugs were given simultaneously, drug resistance did not emerge and lifetime cures of tuberculosis were finally achievable, the explanation of this was that; random bacterial mutations that conferred resistant to individual drugs occurred infrequently during replications. These mutations were unlinked; therefore, the probability of a bacilli spontaneously developing resistance to two drugs was highly improbable. Multi-resistant mutants would be very unlikely to occur, this ultimately eliminating the bacteria from the body.

However as social disruptions became a priory in society, adherence to treatment plans was eroded. As a consequence, the prevalence of drug-resistant strains of M. tuberculosis has risen dramatically in certain regions and populations. At the dawn of the treatment era roughly 1-2% of strains of M. tuberculosis were seen to have significant drug resistance. Tragically, in some developing nations where resources are limited inadequate treatment programs have now resulted in drug-resistant rates in excess of 30%. So how has the resistant evolved? In most instances it because patients either discontinue one or more of their multiple drugs or take less than prescribed. This human intervention creates an environment that selects for survival of the drug-resistant mutants.

In this manner, a gradually increasing portion of the world’s cases involve drug resistant organisms. Most drug-resistant cases have historically involved failed treatments in an individual- an effect from human intervention on evolutionary processes.


This content has been provided by Emma Roache who gave approval for this work to be made publicly available on this website. The author has given due credit to the sources of information. Please respect the author's copyright.

Emma Roache was a VCE student at Hawkesdale P-12 College in 2006. She is currently studying Commerce at Deakin University. She received an enter score of 84.9 (English-42, Further Maths- 38, Accounting- 34, Biology-32, Environmental Science-34)

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