Other Slow-Growing Nontuberculous Mycobacteria

Nontuberculous Mycobacteria, Mucociliary Clearance, and Bronchiectasis

Nontuberculous mycobacteria (NTM) are environmental and ubiquitous, but only a few species are associated with disease, often presented as nodular/bronchiectatic or cavitary pulmonary forms. Bronchiectasis, airways dilatations characterized by chronic productive cough, is the main presentation of NTM pulmonary disease. The current Cole's vicious circle model for bronchiectasis proposes that it progresses from a damaging insult, such as pneumonia, that affects the respiratory epithelium and compromises mucociliary clearance mechanisms, allowing microorganisms to colonize the airways. An important bronchiectasis risk factor is primary ciliary dyskinesia, but other ciliopathies, such as those associated with connective tissue diseases, also seem to facilitate bronchiectasis, as may occur in Lady Windermere syndrome, caused by M. avium infection. Inhaled NTM may become part of the lung microbiome. If the dose is too large, they may grow excessively as a biofilm and lead to disease. The incidence of NTM pulmonary disease has increased in the last two decades, which may have influenced the parallel increase in bronchiectasis incidence. We propose that ciliary dyskinesia is the main promoter of bronchiectasis, and that the bacteria most frequently involved are NTM. Restoration of ciliary function and impairment of mycobacterial biofilm formation may provide effective therapeutic alternatives to antibiotics.

An innovative risk evaluation method on soil pathogens in urban-rural ecosystem

The presence and reproduction of pathogens in soil environment have significant negative impacts on soil security and human health in urban-rural ecosystem. Rapid urbanization has dramatically changed the land use, soil ecosystems, and the presence of pathogens in soil environment, however, the risk associated with soil pathogens remains unknown. Identifying the potential risk of pathogens in soils in urban-rural ecosystem has become an urgent issue. In this study, we established a risk evaluation method for soil pathogens based on analytic hierarchy process and entropy methods to quantitatively estimate the potential risk of soil pathogens to children and adults in urban-rural ecosystem. The abundance and species number of soil pathogens, network structure of soil microbial community, and human exposure factors were considered with 12 indicators to establish the risk evaluation system. The results revealed that 19 potential pathogenic bacteria were detected in soils within a typical urban-rural ecosystem. Substantial differences were observed in both abundance and species of soil pathogens as well as network structure of soil microbial community from urban to rural areas. Urban areas exhibited relatively lower levels of soil pathogenic abundance, but the microbial network was considerably unstable. Rural areas supported relatively higher levels of soil pathogenic abundance and stable microbial networks. Notably, peri-urban areas showed relatively unstable microbial networks alongside higher levels of soil pathogenic abundance compared to other areas. The risk evaluation of soil pathogens for both adults and children showed that peri-urban areas presented the highest potential risk, with children being more susceptible than adults to threats posed by soil pathogens in both urban and peri-urban areas. The established evaluation system provides an innovative approach for quantifying risk of soil pathogens at regional scale and can be used as a reference for preventing soil pathogens contamination and enhancing soil health in areas with intense human activities.

Mycobacterium abscessus HelR interacts with RNA polymerase to confer intrinsic rifamycin resistance

Rifampicin (RIF), the frontline drug against M. tuberculosis, is completely ineffective against M. abscessus, partially due to the presence of an ADP-ribosyltransferase (Arr) that inactivates RIF. Using RNA-seq, we show that exposure of M. abscessus to sublethal doses of RIF and Rifabutin (RBT), a close analog of RIF, results in an ∼25-fold upregulation of Mab_helR in laboratory and clinical isolates. An isogenic deletion in Mab_helR results in RIF/RBT hypersensitivity, and overexpression of Mab_helR confers RIF tolerance in M. tuberculosis. We demonstrate an increased HelR-RNAP association in RIF-exposed bacteria and a MabHelR-mediated dissociation of RNAP from stalled initiation complexes in vitro. Finally, we show that the tip of the PCh-loop of Mab_helR, present in proximity to RIF, is critical for conferring RIF resistance but dispensable for dissociation of stalled RNAP complexes, suggesting that HelR-mediated RIF resistance requires a step in addition to displacement of RIF-stalled RNAP.

Treatment of a mycobacterial infection in an Eastern Long-neck turtle (Chelodina longicollis)

BACKGROUND

Mycobacterial infections are uncommonly diagnosed in reptiles. These infections are often systemic, chronic, and well advanced before presentation and diagnosis. Turtles, both marine and freshwater, appear to have a higher prevalence of the disease than other reptiles, perhaps because of their aquatic environment.

CASE REPORT

An Eastern Long-neck turtle (Chelodina longicollis) was diagnosed with an apparently localised mycobacterial infection in the right foot. Biopsy, culture and PCR were used to make the diagnosis. Treatment with clarithromycin and rifampicin given orally for 9 months appeared to successfully resolve the infection.

CONCLUSION

Antemortem diagnosis is difficult although molecular diagnostic techniques are improving the rates of diagnosis. Treatment of mycobacteria is lengthy, difficult and challenging to the patient, the owner and the veterinarian. For this reason, and because of the potential for zoonotic infection, it is infrequently undertaken.

Evaluation of a new culture medium for isolation of nontuberculous mycobacteria from environmental water samples

Nontuberculous mycobacteria (NTM) are waterborne pathogens commonly found in building water systems where they are a primary concern to vulnerable patient populations and can cause severe disease. The recovery of NTM from environmental samples can be a laborious undertaking and current pre-treatment methods and selective media lack sensitivity. We explored the use of the highly selective Rapidly Growing Mycobacteria (RGM) medium for culturing NTM from environmental water samples compared to existing methods. In total, 223 environmental water samples, including potable and non-potable water, were cultured for NTM using three culture media. In addition to direct culture on RGM medium, each sample was cultured on Middlebrook 7H10 medium and Mitchison 7H11 medium after pre-treatment with 0.2M KCl-HCl. Additionally, 33 distinct species of NTM were inoculated onto RGM medium and 7H10 medium in parallel to directly compare their growth. The use of RGM medium alone without pre-treatment provided a sensitivity (91%) comparable to that offered by culture on both 7H10 and 7H11 with acid pretreatment (combined sensitivity; 86%) with significantly less overgrowth and interference from other organisms on RGM medium. The average concentration of NTM observed on RGM medium alone was comparable to or greater than the NTM concentration on either medium alone or combined. Thirty-three species were examined in parallel and all tested strains of 27 of these species successfully grew on RGM medium, including 19 of 21 from the CDC’s healthcare-associated infections species list. RGM medium was successful at recovering environmental NTM without a pre-treatment, greatly reducing labor and materials required to process samples. Simplification of culture processing for environmental NTM will allow for a better assessment of their presence in building water systems and the potential for reduced exposure of susceptible populations.

Non-tuberculous Mycobacteria can Cause Disseminated Mycobacteriosis in Cats

Mycobacteriosis caused by non-tuberculous mycobacteria (NTM) is a rising concern in human medicine both in immunocompromised and immunocompetent patients. In cats, mycobacteriosis caused by NTM is considered mostly to be a focal or dermal infection, with disseminated disease mostly caused by Mycobacterium avium. We describe three cases of disseminated mycobacteriosis in cats, caused by Mycobacterium malmoense, Mycobacterium branderi/shimoidei and M. avium, with no identified underlying immunosuppression. In all cases, extracellular mycobacteria were seen in the pulmonary epithelium, intestinal lumen and glomerular tufts, which could affect the shedding of the organism. The present study highlights the importance of mycobacteriosis as a differential even in immunocompetent animals. Considering the close relationship of owners and pets and the potential presence of free mycobacteria in secretions, cats should be considered as a possible environmental reservoir for mycobacteria.