A study of the diagnosis, treatment and epidemiology of Mycobacterium abscessus in patients with cystic fibrosis

Preece, Clair (2016) A study of the diagnosis, treatment and epidemiology of Mycobacterium abscessus in patients with cystic fibrosis. Doctoral thesis, Northumbria University.

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Abstract

Members of the Mycobacterium abscessus complex (MABSC) are a highly antibiotic-resistant complex of organisms within the genus Mycobacterium, increasingly acknowledged as a significant cause of lung infection in patients with cystic fibrosis (CF) and associated with poor clinical outcomes. Current methods of isolation of MABSC are hindered by the fact that they grow at a slower rate in culture than other microorganisms with many patient samples having to be discarded due to the overgrowth of more rapidly growing species. Decontamination of samples has shown to have an adverse effect upon the viability of MABSC, therefore improvements in the isolation of MABSC are urgently required in order to offer the possibility of a more rapid and accurate diagnosis.

A novel medium (RGM) was developed for the isolation of MABSC. Commercially available pre-poured media were compared with RGM and challenged with isolates of rapidly growing mycobacteria and other species. In addition, in a multi-centre study sputum samples collected from patients with CF were inoculated onto RGM medium, BCSA and standard automated liquid culture method and assessed for growth. RGM demonstrated superior sensitivity over currently used methods without any requirement for decontamination and could easily be incorporated into any laboratory alongside routine culture for other CF pathogens.

Chromogenic and fluorogenic substrates were investigated for the possibility of differentiating between subspecies within the MABSC complex. However, the results established that these would not provide any additional benefit to RGM.

Possible environmental sources were explored in order to establish how patients with CF were acquiring MABSC. Although person-to-person transmission has been suggested, there are very few reports to substantiate this at present and many questions remain unanswered. In this study, MABSC was not isolated from any of the environments screened.

Finally, a selection of antimicrobials were investigated against MABSC with the purpose of ascertaining susceptibility and whether any may be used for a more successful treatment outcome. There were no clinically applicable results therefore further work is required in this area.

To conclude, RGM is a novel culture medium, which can be embedded alongside routine culture for other CF pathogens without any requirement for decontamination. This means that all respiratory samples submitted from patients with CF can be conveniently cultured for NTM, considerably improving the service offered to clinicians and patients. Furthermore, it is likely that formal AFB culture methods could be replaced by use of such a medium, potentially enabling substantial savings in terms of materials and labour time.

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