Two Studies Evaluate Non-Tuberculous Mycobacterium Causes and Identification

Non-tuberculous mycobacterium (NTM), a serious lung disease, can be identified in different ways in patients. Recently, 2 studies evaluated specific identification and causes of NTM in order to help predict treatment outcomes in the future.

Currently, NTM is frequently not identified using 16S rRNA sequencing, even for samples with positive cultures for these organisms. Since NTM typically has only 1 or 2 copies per genome, they may be underrepresented—therefore, the standard 16S sequencing may not be the best identification method.

One study, recently presented at The American Thoracic Society 2018 International Conference, investigated the airway microbiota in patients with bronchiectasis using a different sequencing method—one that was biased towards mycobacterium to help identify low abundance organisms.¹

The study included 20 subjects with lower airway sampling and the 16S rRNA gene sequence was used to analyze the microbiome composition. Also, a nested mycobacteriome polymerase chain reaction (PCR) approach was used to analyze the bronchoalveolar lavage (BAL) samples. Then, this approach was validated with a larger cohort with samples collected from patients with bronchiectasis, according to the study.

The BAL samples detected mycobacterium in 4 samples with standard 16S rRNA gene sequencing approaches. The nested mycobacterium approach was able to detect mycobacterium in the same 4 samples, as well as 3 other culture positive samples with sequences that match mycobacterium avium. Additionally, 1 NTM culture negative sample with mycobacterium was identified.

“The low abundance of Mycobacterium in NTM+ samples supports prior data showing that a 16S approach may under-represent this genus,” concluded the study. “Addition of Mycobacterium specific primers help further describe the microbiome in this disease.”

The other study focused on evaluation of the clinical characteristics and treatment outcomes in patients with NTM lung disease (NTM-LD) caused by mixed infection with two major NTM pathogens—mycobacterium avium complex (MAC) and M. abscessus complex (MABC).²

The study included 71 consecutive patients who were diagnosed with NTM-LD caused by mixed infection with MAC and MABC between 2010 and 2015. The treatment outcome was evaluated at 12 months after antibiotic treatment and sputum conversion was defined as 3 consecutive negative cultures of all NTM organisms.

The results demonstrated that mixed infection with MAC and M. massiliense was more common (66%) than MAC and M. abscessus (34%). Additionally, M. avium was frequently associated with M. massiliense, while M. intracellulare was associated with M. abscessus. Sputum culture conversion rates were found to be lower in patients infected with MAC and M. abscessus than those with MAC and M. massiliense.

“Mixed infection with MAC and MABC typically developed in patients with nodular bronchiectatic form of NTM-LD,” the study concluded. “Precise identification of etiologic NTM organisms could help predict treatment outcomes in these patients.”

References

1. Sulaiman I, Wu B, Scaglione BD, et al. The mycobacteriome: A nested approach to identify non-tuberculous mycobacterium. Presented at the American Thoracic Society 2018 International Conference; San Diego, California; May 18-23, 2018; Abstract 9969.

2. Shin S, Jhun B, Choe J, et al. Nontuberculous mycobacterial lung diseases caused by mixed infection with mycobacterium avium complex and mycobacterium abscessus complex. Presented at the American Thoracic Society 2018 International Conference; San Diego, California; May 18-23, 2018; Abstract 2602.