Understanding the mechanisms of drug resistance in enhancing rapid molecular detection of drug resistance in Mycobacterium tuberculosis

[摘要] One of the aims of direct observed therapy strategy implemented by the World HealthOrganization was to prevent the development of drug resistant tuberculosis. However, in recentyears a dramatic increase and spread in multidrug resistant tuberculosis has been observed. Inthis study, a molecular epidemiological approach was used to understand and rapidly detect drugresistance in high incidence tuberculosis communities of the Western Cape, South Africa.Previous studies showed that, drug resistant tuberculosis occurs as a result of spontaneousmutations in particular genes. Using molecular techniques, we developed an algorithm to rapidlydetect isoniazid, rifampicin and ethambutol drug resistance in tuberculosis patients from a shortterm mini culture. Rapid detection of drug resistance is important to prevent future transmissionevents. In addition, accurate ethambutol resistance testing is of particular importance, sincetreatment of patients infected with multidrug resistant strains with second line anti-tuberculosisdrugs depend on the ethambutol test results. In a comprehensive study, we found that thealgorithm performs well when compared to the traditional culture method currently used by theroutine laboratories. However, the results showed that more then 90 % of ethambutol resistanceis missed by the routine laboratories. This has important implications for the tuberculosis controlprogram, since patients infected with the drug resistant strain may be on inappropriate treatment.In this study, we found that certain strains have a selective advantage to become drug resistantand transmit and this implies that they are more virulent and fit than other strains. Thisobservation has also been made for strains within the same genotype family. The moretransmissible drug resistant strains cause large drug resistant outbreaks. This study highlights the complexity of the drug resistant epidemic, and confirms that it is amajor problem in local communities. Application of molecular methods has provided us withtools to study how resistance might develop. We have demonstrated how we made use of anewly developed method to detect a multidrug resistant outbreak in the study community. Theapplications of transcriptomics identified several genes that might play a role in isoniazidresistance. Using this data a model was proposed whereby isoniazid resistant strains cancompensate for the toxic effect of the drug. Application of comparative genomics by wholegenome sequencing will be used to assist us in the further understanding of the mechanisms ofdrug resistance.This study also conclude that we should continue in our attempts to develop faster diagnosticsfor both first and second line drugs and that we must not loose site that all of this research mustin the end benefit the patients.

[发布机构] Stellenbosch University