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Numerous Non-Tuberculosis Mycobacteria Identified in Saudi Arabian Infections

NEW YORK (GenomeWeb) – Saudi Arabian researchers reported this week that they have identified rare, non-tuberculosis Mycobacterium species as the apparent culprits behind pulmonary and extra-pulmonary infections in that country.

The team did targeted sequencing, including16S ribosomal RNA gene sequencing, on more than two-dozen clinical isolates collected in Saudi Arabia as part of a national surveillance program focused on non-tuberculosis mycobacteria (NTM). The analysis, published in PLOS Neglected Tropical Diseases yesterday, uncovered 16 different NTM species, with M. monascence turning up in nearly one-fifth of the cases considered.

"As the first report on the existence of rare NTM species in Saudi Arabia, the findings showed an alarming diversity of clinically relevant NTMs causing both pulmonary and extra-pulmonary diseases," senior author Sahal Al-Hajoj, an infection and immunity researcher at the King Faisal Specialist Hospital and Research Centre, and co-authors wrote.

There are hints that non-tuberculosis mycobacteria may be behind an increasing number of lung and extra-pulmonary infections, the team explained, though questions remain regarding the actual rates of these infections, the relative pathogenicity of various NTM species, and the clinical features associated with these bacteria, if any.

"[T]he identification [of NTMs] in diagnostic laboratories is mostly limited to common species," the authors wrote, noting that the "impact of NTM species diversity on clinical outcome is so far neglected in most of the clinical settings."

Starting with 510 suspicious clinical isolates collected between the spring of 2014 and fall of 2015 as part of a national surveillance program in Saudi Arabia, the researchers used line probe MTBC genotyping assays to narrow in on 27 isolates that appeared most likely to contain non-tuberculosis mycobacteria — isolates obtained from 16 pulmonary cases and 11 cases involving skin infections or other extra-pulmonary features.

Almost 80 percent of the infections affected men, they noted, and seven of the individuals had documented tuberculosis infections in the past. When additional clinical criteria were considered, four of the lung cases were classified as colonization rather than infections.

After doing targeted sequencing on four gene regions — 16S rRNA, rpoB, hsp65, and 16S-23S internal transcribed spacer (ITS) genes — the team used BLAST analyses against available sequence databases to identify 16 NTM species.

The researchers identified M. monascence in 18.5 percent of the cases, followed by M. cosmeticum and M. kubicae, which were each linked to 11.1 percent of cases. Three more species had 7.4 percent prevalence, they reported, while the remaining 10 species were each identified in a single case. 

The authors went on to analyze clinical features associated with these NTMs, identifying species that tended to turn up at specific infections sites. Based on their results, they suggested that "Saudi Arabia faces [a] serious threat from rare NTM species with high clinical significance." They suggested that upgrades to the country's diagnostic facilities or strategies may be needed to effectively identify and treat infections involving rare NTMs in the future.