Mycobacterium abscessus: an emerging rapid-growing potential pathogen. Review article

Mycobacterium abscessus from respiratory isolates: activities of drug combinations

Mycobacterium abscessus is the most resistant of rapidly growing pathogenic mycobacteria. We performed a screening of the in vitro sterilizing capacity of various antibiotic combinations against two strains isolated from respiratory samples (in vitro activity of each antibiotic: 51 combinations of two drugs and 47 of three drugs). Our findings confirm that clarithromycin is the most useful drug. The combination of this drug with linezolid exhibits good activity. In addition, the fluoroquinolones and rifabutin in association with clarithromycin may have clinical utility because they are administered orally. Therapeutic alternatives in this type of infections should be evaluated in greater depth.

A novel gene, erm(41), confers inducible macrolide resistance to clinical isolates of Mycobacterium abscessus but is absent from Mycobacterium chelonae

Mycobacterium abscessus infections tend to respond poorly to macrolide-based chemotherapy, even though the organisms appear to be susceptible to clarithromycin. Circumstantial evidence suggested that at least some M. abscessus isolates might be inducibly resistant to macrolides. Thus, the purpose of this study was to investigate the macrolide phenotype of M. abscessus clinical isolates. Inducible resistance to clarithromycin (MIC > 32 microg/ml) was found for 7 of 10 clinical isolates of M. abscessus previously considered susceptible; the remaining 3 isolates were deemed to be susceptible (MIC <or= 0.5 microg/ml). Inducible resistance was conferred by a novel erm gene, erm(41), which was present in all 10 isolates and in an isolate of Mycobacterium bolletii (M. abscessus type II). However, the erm(41) alleles were nonfunctional in the three susceptible M. abscessus isolates. No evidence of erm(41) was found in Mycobacterium chelonae, and an isolate of Mycobacterium massiliense appeared to be an erm(41) deletion mutant. Expression of erm(41) in M. abscessus conferred resistance to clarithromycin and erythromycin and the ketolide HMR3004. However, this species was found to be intrinsically resistant, independent of erm(41), to clindamycin, quinupristin (streptogramin B), and telithromycin. The ability to confer resistance to clindamycin and telithromycin, but not quinupristin, was demonstrated by expressing erm(41) in Maycobacterium smegmatis. Exposure of M. abscessus to the macrolide-lincosamide-streptogramin B-ketolide agents increased the levels of erm(41) mRNA 23- to 250-fold within 24 h. The inducible macrolide resistance phenotype of some M. abscessus isolates may explain the lack of efficacy of macrolide-based chemotherapy against this organism.

The antioxidant mimetic, MnTE-2-PyP, reduces intracellular growth of Mycobacterium abscessus

Mycobacterium abscessus is a rapidly growing environmental mycobacterium that can cause severe skin, soft tissue, and lung infections. M. abscessus grows inside macrophages, and these cells release a vast number of proinflammatory cytokines in response to infections. The metalloporphyrin, MnTE-2-PyP, is a broad antioxidant that reduces inflammatory cell signaling. Macrophage-like THP-1 cells were infected with M. abscessus in the presence or absence of MnTE-2-PyP. MnTE-2-PyP significantly decreased, in a dose-dependent manner, the number of M. abscessus organisms recovered from infected THP-1 cells 4 and 8 days after infection. Furthermore, when combined with clarithromycin, MnTE-2-PyP additively reduced the number of cells associated with M. abscessus. A mechanism of bacterial growth inhibition by MnTE-2-PyP was then elucidated. It was found that MnTE-2-PyP promoted the survival of infected THP-1 cells and increased fusion of M. abscessus-containing phagosomes with lysosomes.

Biofilm development by potentially pathogenic non-pigmented rapidly growing mycobacteria

BACKGROUND

A study to evaluate the biofilm-development ability in three different media (Middlebrook 7H9, sterile tap water and PBS-5% glucose) was performed with 19 collection strains from 15 different species on non-pigmented rapidly growing mycobacteria (NPRGM). A microtiter plate assay was developed to evaluate the percentage of covered surface of the microtiter plate wells in different days from day 1 to day 69.

RESULTS

All strains were able to develop biofilm in all the tested media. Middlebrook 7H9 showed the fastest growth, followed by sterile tap water and PBS-5% glucose. A sigmoid growth curve was detected in all the strains both in Middlebrook 7H9 and in sterile tap water. A difference could be detected for Mycobacterium abscessus in tap water, where it showed faster growth than all the other strains.

CONCLUSION

Biofilm development seems to be a property of all the species of NPRGM and it depends on the nutrients present in the medium. The microtiter plate assay described here is a useful tool to evaluate differences in biofilm development among the different species of rapidly growing mycobacteria.

Mycobacterium abscessus and M. avium trigger Toll-like receptor 2 and distinct cytokine response in human cells

Mycobacterium avium (MAV) and M. abscessus (MAB) are ubiquitous environmental organisms increasingly recognized to cause chronic lung disease in patients with apparently normal immune function. Little is yet known about their human pathophysiology. Our objective was to examine cytokine and chemokine responses (protein and gene expression) and signaling pathways triggered by reference and clinical isolates of MAB and MAV in human peripheral blood mononuclear cells, monocytes, and murine bone marrow-derived macrophages in vitro. MAB-induced TNF-alpha production was higher than that induced by MAV. IFN-gamma, IL-1beta, and the chemokines macrophage inflammatory protein-1alpha and regulated on activation, normal T cell expressed and secreted were equally up-regulated. Differences between MAB and MAV do not require replication and are heat stable. We found no differential effect due to rough or smooth colonies within the same species. Similar to MAV, MAB triggered mitogen-activated protein kinase (MAPK) signaling and nuclear factor-kappaB translocation. Induction of TNF-alpha was dependent on MAPK pathways, since pre-incubation of cells with signaling inhibitors led to more than 85% reduction in cytokine secretion. MAB also triggered a Toll-like receptor 2 (TLR2)-mediated response that led to TNF-alpha production by human monocytes. Accordingly, stimulation of murine TLR2- or myeloid differentiation factor 88-deficient bone marrow-derived macrophages did not elicit TNF-alpha, reinforcing a critical role for TLR2 in MAB-induced cell activation. We concluded that MAB signals human cells through MAPK and TLR2 pathways and triggers more pronounced pro-inflammatory cytokines and chemokines than MAV.

Late-onset posttraumatic skin and soft-tissue infections caused by rapid-growing mycobacteria in tsunami survivors

BACKGROUND

In the tsunami catastrophe in Thailand in 2004, several thousand Swedish tourists were injured, with contaminated crush trauma of the legs being the main cause of injury among the survivors.

METHODS

Patient and laboratory data for those who received hospital care in Stockholm and Gothenburg and contracted late-onset infections due to rapid-growing mycobacteria were reviewed retrospectively. Also, concomitant infections were recorded.

RESULTS

Fifteen patients with late-onset skin and soft-tissue infections due to rapid-growing mycobacteria are described here. Mycobacterium abscessus was isolated in 7 cases, Mycobacterium fortuitum was isolated in 6 cases, and Mycobacterium peregrinum and Mycobacterium mageritense were isolated in 1 case each. The infections appeared after a delay of 20-105 days (median, 60 days) after the trauma, targeting undamaged skin located near primary sutured wounds or skin grafts. Antimycobacterial drugs were given to 9 (60%) of the patients. The course of infection was protracted, but all infections due to rapid-growing mycobacteria healed within 12 months. Concomitant subcutaneous infections due to other microorganisms, such as Burkholderia pseudomallei or Cladophialophora bantiana, appeared early or late after the trauma.

CONCLUSIONS

Repeated cultures of abscess and wound specimens for Mycobacterium species may be needed to find the etiologic agents causing contaminated skin and soft-tissue infections, such as those that developed after traumas that occurred during the tsunami. These cultures are especially necessary when symptoms appear late and when conventional bacterial culture results are negative. A biopsy is recommended for the best yield and for complementary histopathological examination.

Mastoiditis secondary to mycobacterium abscessus imaged with gallium-67 scintigraphy

Atypical mycobacterium is rarely seen as a cause of chronic mastoiditis but has been increasingly recognized over the past few years. Mycobacterium abscessus is the most pathogenic and chemotherapy-resistant, rapid-growing mycobacterium of all the four groups. This paper presents a case of a 57-year-old woman who had chronic mastoiditis with recurrent exacerbations. The initial computed tomography (CT) findings showed the presence of an inflammatory process and she was treated with the appropriate antibiotics. The patient subsequently underwent a tissue biopsy when she presented with another exacerbation. At this time, the CT scan did not identify the ongoing exacerbation, but the Gallium-67 scintigraphy did.

Differential antibiotic susceptibility of Mycobacterium abscessus variants in biofilms and macrophages compared to that of planktonic bacteria

Mycobacterium abscessus causes refractory pulmonary infections requiring surgery for cure. It exists as a smooth biofilm-forming phenotype which is noninvasive and a rough, non-biofilm-forming phenotype which can invade macrophages and cause persistent pulmonary infection in mice. We have postulated that the dissociation of the smooth phenotype to the rough phenotype may lead to invasive lung disease following initial colonization of the airways. Amikacin, cefoxitin, and clarithromycin are standard therapies for this infection. We determined the MICs of these antibiotics against this pathogen in biofilms and macrophages, the niches that it likely occupies in the human host. Our results demonstrate that even though the MICs indicate sensitivity to these antibiotics, the minimal bactericidal concentrations for amikacin and clarithromycin were substantially higher and were out of the range of the concentrations achievable in serum. Cefoxitin demonstrated only bacteriostatic activity. In addition, although amikacin had modest activity against M. abscessus in biofilms, clarithromycin demonstrated only minimal activity at the highest concentrations tested. Our results indicate that M. abscessus in mature biofilms is in a stationary-phase state and that clarithromycin is relatively inactive against stationary-phase M. abscessus. In human macrophages, all three antibiotics were only bacteriostatic for M. abscessus variants at 10 times their MICs. These results suggest why treatment failure with antibiotics alone is common in the clinical setting of M. abscessus pulmonary infection. Determination of the efficacies of new antibiotics should include an assessment of their activities against the smooth and rough M. abscessus morphotypes in biofilms and macrophages.

Iris root abscess and necrotizing sclerokeratitis caused by Mycobacterium abscessus and presenting as hemorrhagic anterior uveitis

PURPOSE

To report a case of an iris abscess and necrotizing sclerokeratitis caused by Mycobacterium abscessus and presenting as hemorrhagic uveitis.

METHODS

An 86-year-old white woman was diagnosed with hemorrhagic anterior uveitis and treated with high-frequency topical steroids. The inflammation progressed to involve the cornea and the sclera, and the treatment was changed to intensive antibiotics. There was no improvement. Direct microscopy of a biopsy specimen of the lesion wrongly identified Nocardia as the cause, but antibiotic sensitivity suggested clarithromycin as a suitable therapeutic agent. Therapy was changed but there was continued deterioration. The eye could not be saved and the causative organism was subsequently discovered to be M. abscessus.

RESULTS

The eye was enucleated 6 months after initial presentation.

CONCLUSIONS

Ocular infection with M. abscessus is an extremely rare cause of necrotizing sclerokeratitis and may present as a hemorrhagic uveitis. There is a high risk of misdiagnosis and late detection, which may have severe consequences.

Localised pyogranulomatous dermatitis due to Mycobacterium abscessus in a cat: a case report

A case of pyogranulomatous dermatitis, caused by Mycobacterium abscessus, an unusual opportunistic Mycobacterium spp., is described in a cat. Histopathological examination of the affected skin confirmed the diagnosis and Ziehl-Neelsen staining revealed acid-fast rods. A rapidly growing mycobacterium was found after culture on a Löwenstein-Jensen medium. Real-time polymerase chain reaction for the 16S rDNA (434bp) sequence and the sequence of the rpoB gene (359bp) revealed 99% and 100% matches, respectively, with M. abscessus. This is the first report of a feline infection caused by this organism in Europe.

Importance of T cells, gamma interferon, and tumor necrosis factor in immune control of the rapid grower Mycobacterium abscessus in C57BL/6 mice

Mycobacterium abscessus is an emerging rapidly growing mycobacterium that causes tuberculous-like lesions in humans. We studied the immune control of this organism in C57BL/6 mice challenged intravenously with 10(7) CFU. Bacteria were eliminated from both the spleen and the liver within 90 days, and liver histology showed organized granulomatous lesions. A T- and B-cell requirement was investigated by challenging Rag2-/-, Cd3epsilon-/-, and muMT-/- mice. Rag2-/- and Cd3epsilon-/- mice were significantly impaired in the ability to clear M. abscessus from the liver and spleen, and muMT-/- mice were significantly impaired in the ability to clear M. abscessus from the liver, suggesting that infection control was primarily T cell dependent in the spleen and both T and B cell dependent in the liver. The liver granulomatous response was similar to that of wild-type controls in muMT-/- mice but completely absent in Cd3epsilon-/- and Rag2-/- mice. We studied the involvement of gamma interferon (IFN-gamma) and tumor necrosis factor (TNF) by challenging C57BL/6 mice deficient in the IFN-gamma receptor (Ifngr1-/-) and in TNF (Tnf-/-). Ifngr1-/- mice were significantly impaired in M. abscessus control both in the spleen and in the liver, and granulomas were profoundly altered. The effect was even more substantial in Tnf-/- mice; they failed to control M. abscessus infection in the liver and died within 20 to 25 days after infection with many hepatic inflammatory foci and major lesions of ischemic necrosis in the liver and kidney. These features were not observed with the closely related species M. chelonae. T-cell immunity, IFN-gamma, and TNF are central factors for the control of M. abscessus in C57BL/6 mice, as they are for the control of pathogenic slowly growing mycobacteria.

Use of a colorimetric assay to measure differences in cytotoxicity of Mycobacterium tuberculosis strains

Several techniques have been used to quantify the cytotoxicity produced by Mycobacterium tuberculosis bacilli on cell monolayers; however, they are semi-quantitative or time consuming. Herein, a method based on crystal violet (CV) uptake by THP-1 cell monolayers is described. This colorimetric method quantifies the cytotoxic effect as a function of the number of remaining cells after the infection with M. tuberculosis. Since this micro-organism is not stained by the dye, it does not produce a background that affects absorbance readings. As determined by CV assay (CVA), M. tuberculosis strain H37Rv destroyed 10.5 % of THP-1 cell monolayers at 24 h and 50.52 % at 72 h, while M. tuberculosis strains lacking the complete phospholipase C locus produced a reduced cytotoxic effect. The damage estimated by microscopy corresponded to the effect quantified by CVA. The results show that the use of CVA is a rapid, sensitive and reliable quantitative assay to measure the cytotoxicity of different M. tuberculosis strains.

Atypische Mykobakteriose der Haut durch Mycobacterium abscessus bei einer immunkompetenten Frau

Mycobacterium abscessus is the most pathogenic of the fast-growing mycobacteria, and it is resistant to most of the antimicrobial and tuberculostatic drugs available. This non-tuberculous mycobacterium is significant in medicine because it can contaminate post-traumatic wounds and be a causative agent in chronic skin and soft tissue infection after surgical procedures.A 60-year-old immunocompetent woman was suffering from chronic ulcers and abscesses on the heels and malleoli of both feet. Histological examination revealed a granulomatous inflammation with detection of acid-fast rods, albeit without fibrinoid necrosis. The repeated detection of atypical mycobacteria, which were ultimately identified as Mycobacterium abscessus, allowed the diagnosis of an atypical mycobacteriosis of the skin. This was successfully treated first with clarithromycin and rifabutin and later with a combination of ethambutol, minocycline, clofazimine and azithromycin.

In Vitro activities of isepamicin, other aminoglycosides, and capreomycin against clinical isolates of rapidly growing mycobacteria in Taiwan

The in vitro activities of isepamicin against 117 Mycobacteria abscessus, 48 Mycobacterium fortuitum, and 20 Mycobacterium chelonae isolates were evaluated by a microdilution test. Isepamicin MIC(90)s were < or =16 microg/ml for the three species. Isepamicin was as active as amikacin and kanamycin and more active than tobramycin, capreomycin, gentamicin, and streptomycin.