Treatment of Mycobacterium abscessus Infection

Risk Factors for and Outcomes Following Early Acquisition of Mycobacterium abscessus Complex After Lung Transplantation

Background

Lung transplant recipients are at increased risk of Mycobacterium abscessus complex (MABC) acquisition and invasive infection. We analyzed risk factors and outcomes of early post-lung transplant MABC acquisition.

Methods

We conducted a retrospective matched case-control study of patients who underwent lung transplant from 1/1/2012 to 12/31/2021 at a single large tertiary care facility. Cases had de novo MABC isolation within 90 days post-transplant. Controls had no positive MABC cultures and were matched 3:1 with cases based on age and transplant date. Recipient demographics and pre-/peri-operative characteristics were analyzed, and a regression model was used to determine independent risk factors for MABC acquisition. We also assessed 1-year post-transplant outcomes, including mortality.

Results

Among 1145 lung transplants, we identified 79 cases and 237 matched controls. Post-transplant mechanical ventilation for >48 hours was independently associated with MABC acquisition (adjusted odds ratio, 2.46; 95% CI, 1.29-4.72; P = .007). Compared with controls, cases required more days of hospitalization after the MABC index date (28 vs 12 days; P = .01) and had decreased 1-year post-transplant survival (78% vs 89%; log-rank P = .02). One-year mortality appeared highest for cases who acquired M. abscessus subsp. abscessus (31% mortality) or had extrapulmonary infections (43% mortality).

Conclusions

In this large case-control study, prolonged post-transplant ventilator duration was associated with early post-lung transplant MABC acquisition, which in turn was associated with increased hospital-days and mortality. Further studies are needed to determine the best strategies for MABC prevention, surveillance, and management.

Complicated Surgical Site Infection with Mycobacterium Abscessus After Liposuction and Affections of Corticosteroids in the Treatment Regimen: Three Cases Report and a Systematic Review

INTRODUCTION

Mycobacterium abscessus infection after liposuction/fat grafting is a rare complication that is hard to diagnose and treat. Misdiagnosis could result in treatment failure and prolonged hospital stays. The paradoxical reaction is another complication that rarely occurs in non-HIV patients infected with nontuberculosis mycobacteria. This study reported 3 cases infected with M. abscessus complicated by the paradoxical reaction after liposuction and fat grafting. It highlighted characteristics giving clues of the paradoxical reaction and a successful strategy. Also, a systematic review was conducted to comprehensively provide varied aspects of M. abscessus infection after liposuction and/or fat grafting.

METHODS

Three cases were retrospectively included reporting data characteristics of patients, cosmetic procedures, and treatment strategy. PubMed, Scopus, Virtual Health Library (VHL), and Global Health Library (GHL) were searched to find and include cases with M. abscessus infection after liposuction and/or fat grafting based on defined selection criteria. Relevant data were extracted and summarized. The risk of bias in included studies was assessed using JBI critical appraisal checklists.

RESULTS

Twenty-four articles were included in the systematic review. Symptoms often developed approximately 1 month after the cosmetic surgery. Culture, AFB, and PCR were common methods of diagnosis of M. abscessus after liposuction and/or fat grafting. It took about 33 days on average from the presentation to isolate and detect the pathogens. Antibiotics based on susceptibility testing results along with surgical interventions were effective methods of treatment. Our three cases which were complicated by the paradox were addressed by adding methylprednisolone for 2 weeks to the macrolide-based therapy.

CONCLUSIONS

Awareness of this disease should be widely raised among physicians for early diagnosis and proper treatments. Cultures of specimens and AFB should be repeated many times before excluding the possibility of Mycobacterium spp. A paradoxical reaction should be suspected if the symptoms were worse after the antibiotic therapy based on susceptibility testing results and proper surgical interventions, especially if patients had taken corticosteroids before being admitted.

LEVEL OF EVIDENCE III

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Eradication of Nontuberculous Mycobacteria in People with Cystic Fibrosis Treated with Elexacaftor/Tezacaftor/Ivacaftor: A Multicenter Cohort Study

BACKGROUND

The prevalence of nontuberculous mycobacteria (NTM) infections is rising in people with cystic fibrosis (pwCF). NTM infection, especially infection with Mycobacterium abscessus complex (MABC), is commonly associated with severe lung deterioration. The current treatment modalities, including multiple intravenous antibiotics, frequently fail to achieve airway eradication. Although treatment with elexacaftor/tezacaftor/ivacaftor (ETI) has been shown to modulate the lung microbiome, data regarding its role in eradicating NTM in pwCF is lacking. Our aim was to evaluate the impact of ETI on the rate of NTM eradication in pwCF.

METHODS

This retrospective multicenter cohort study included pwCF from five CF centers in Israel. PwCF aged older than 6 who had at least one positive NTM airway culture in the past two years and were treated with ETI for at least one year were included. The annual NTM and bacterial isolations, pulmonary function tests, and body mass index were analyzed before and after ETI treatment.

RESULTS

Fifteen pwCF were included (median age 20.9 years, 73.3% females, 80% pancreatic insufficient). In nine patients (66%) NTM isolations were eradicated following treatment with ETI. Seven of them had MABC. The median time between the first NTM isolation and treatment with ETI was 2.71 years (0.27-10.35 years). Eradication of NTM was associated with improved pulmonary function tests (p<0.05).

CONCLUSIONS

For the first time, we report successful eradication of NTM, including MABC, following treatment with ETI in pwCF. Additional studies are needed to assess whether treatment with ETI can result in the long-term eradication of NTM.

Prolonged Survival Following Intra-abdominal Mycobacterium abscessus Infection Without Antimicrobial Therapy or Surgical Intervention

Management of Mycobacterium abscessus infection involves prolonged multidrug antibiotic therapy with surgical resection indicated in extensive disease and abscesses. We report a case of post-surgical intra-abdominal M. abscessus infection with prolonged survival and radiographic resolution without intervention. A 51-year-old female who had a prolonged hospital stay with multiple surgeries following a complicated laparoscopic sleeve gastrectomy developed multiple M. abscessus intra-abdominal and abdominal wall abscesses with cutaneous fistulae. She was started on a multidrug antibiotic regimen. However, the patient terminated the regimen after 4 weeks due to intolerable side effects and was transitioned to hospice care. She showed steady clinical improvement with radiographic resolution of the abscesses over the next year. In the context of the limited understanding of these infections, our finding is notable, given that in this period, she avoided potential hospitalizations, life altering side effects of prolonged antimicrobial therapy, and complications from more surgeries.

Conjugation of Vancomycin with a Single Arginine Improves Efficacy against Mycobacteria by More Effective Peptidoglycan Targeting

Drug resistant bacterial infections have emerged as one of the greatest threats to public health. The discovery and development of new antimicrobials and anti-infective strategies are urgently needed to address this challenge. Vancomycin is one of the most important antibiotics for the treatment of Gram-positive infections. Here, we introduce the vancomycin-arginine conjugate (V-R) as a highly effective antimicrobial against actively growing mycobacteria and difficult-to-treat mycobacterial biofilm populations. Further improvement in efficacy through combination treatment of V-R to inhibit peptidoglycan synthesis and ethambutol to inhibit arabinogalactan synthesis underscores the ability to identify compound synergies to more effectively target the Achilles heel of the cell-wall assembly. Moreover, we introduce mechanistic activity data and a molecular model derived from a d-Ala-d-Ala-bound vancomycin structure that we hypothesize underlies the molecular basis for the antibacterial improvement attributed to the arginine modification that is specific to peptidoglycan chemistry employed by mycobacteria and distinct from Gram-positive pathogens.

Mycobacterium abscessus Meningitis Associated with Stem Cell Treatment During Medical Tourism

Mycobacterium abscessus infections have been reported as adverse events related to medical tourism. We report M. abscessus meningitis in a patient who traveled from Colorado, USA, to Mexico to receive intrathecal stem cell injections as treatment for multiple sclerosis. We also review the management of this challenging central nervous system infection.

The small non-coding RNA B11 regulates multiple facets of Mycobacterium abscessus virulence

Mycobacterium abscessus causes severe disease in patients with cystic fibrosis. Little is known in M. abscessus about the roles of small regulatory RNAs (sRNA) in gene regulation. We show that the sRNA B11 controls gene expression and virulence-associated phenotypes in this pathogen. B11 deletion from the smooth strain ATCC_19977 produced a rough strain, increased pro-inflammatory signaling and virulence in multiple infection models, and increased resistance to antibiotics. Examination of clinical isolate cohorts identified isolates with B11 mutations or reduced expression. We used RNAseq and proteomics to investigate the effects of B11 on gene expression and test the impact of mutations found in clinical isolates. Over 200 genes were differentially expressed in the deletion mutant. Strains with the clinical B11 mutations showed expression trends similar to the deletion mutant, suggesting partial loss of function. Among genes upregulated in the B11 mutant, there was a strong enrichment for genes with B11-complementary sequences in their predicted ribosome binding sites (RBS), consistent with B11 functioning as a negative regulator that represses translation via base-pairing to RBSs. Comparing the proteomes similarly revealed that upregulated proteins were strongly enriched for B11-complementary sequences. Intriguingly, genes upregulated in the absence of B11 included components of the ESX-4 secretion system, critical for M. abscessus virulence. Many of these genes had B11-complementary sequences at their RBSs, which we show is sufficient to mediate repression by B11 through direct binding. Altogether, our data show that B11 acts as a direct negative regulator and mediates (likely indirect) positive regulation with pleiotropic effects on gene expression and clinically important phenotypes in M. abscessus. The presence of hypomorphic B11 mutations in clinical strains is consistent with the idea that lower B11 activity may be advantageous for M. abscessus in some clinical contexts. This is the first report on an sRNA role in M. abscessus.

Epidemiology, management, and clinical outcomes of extrapulmonary Mycobacterium abscessus complex infections in heart transplant and ventricular assist device recipients

Nontuberculous mycobacteria are emerging pathogens, yet data on the epidemiology and management of extrapulmonary nontuberculous mycobacteria infections in orthotopic heart transplantation (OHT) and ventricular assist device (VAD) recipients are scarce. We retrospectively reviewed records of OHT and VAD recipients who underwent cardiac surgery at our hospital and developed Mycobacterium abscessus complex (MABC) infection from 2013 to 2016 during a hospital outbreak of MABC linked to heater-cooler units. We analyzed patient characteristics, medical and surgical management, and long-term outcomes. Ten OHT patients and 7 patients with VAD developed extrapulmonary M. abscessus subspecies abscessus infection. The median time from presumed inoculation during cardiac surgery to the first positive culture was 106 days in OHT and 29 days in VAD recipients. The most common sites of positive cultures were blood (n = 12), sternum/mediastinum (n = 8), and the VAD driveline exit site (n = 7). The 14 patients diagnosed when alive received combination antimicrobial therapy for a median of 21 weeks, developed 28 antibiotic-related adverse events, and underwent 27 surgeries. Only 8 (47%) patients survived longer than 12 weeks after diagnosis, including 2 patients with VAD who experienced long-term survival after an explantation of infected VADs and OHT. Despite aggressive medical and surgical management, OHT and VAD patients with MABC infection experienced substantial morbidity and mortality.

Mycobacterium abscessus VapC5 toxin potentiates evasion of antibiotic killing by ribosome overproduction and activation of multiple resistance pathways

Mycobacterium abscessus (Mab) infections are inexplicably intractable to clearing after aggressive and lengthy treatment regimens. Here we discovered that acquisition of a single toxin-antitoxin system enables Mab to activate a phenotypic switch that enhances survival upon treatment with current first-line antibiotics. This switch is tripped when the VapC5 toxin inactivates tRNASerCGA by cleavage at only one site within its anticodon, leading to growth arrest. Concomitant tRNASerCGA depletion then reprograms the transcriptome to favor synthesis of proteins naturally low in the cognate Ser UCG codon including the transcription factor WhiB7 and members of its regulon as well as the ribosomal protein family. This programmed stockpiling of ribosomes is predicted to override the efficacy of ribosome-targeting antibiotics while the growth arrest phenotype attenuates antibiotics targeting cell wall synthesis. In agreement, VapC5 increases Mab persister formation upon exposure to amikacin and the next-generation oxazolidinone tedizolid (both target ribosomes) or cefoxitin (inhibits cell wall synthesis). These findings expand the repertoire of genetic adaptations harnessed by Mab to survive assaults intended to eradicate it, as well as provide a much-needed framework for selection of shorter and more efficacious alternate treatment options for Mab infections using currently available antimicrobials whose targets are not confounded by VapC5.

Ferritin from Mycobacterium abscessus is involved in resistance to antibiotics and oxidative stress

Mycobacterium abscessus subsp. massiliense (Mycma) is a rapidly growing Mycobacterium belonging to the M. abscessus complex that is often associated with lung and soft tissue infection outbreaks. Mycma is resistant to many antimicrobials, including those used for treating tuberculosis. Therefore, Mycma infections are difficult to treat and may lead to high infectious complication rates. Iron is essential for bacterial growth and establishment of infection. During infection, the host reduces iron concentrations as a defense mechanism. To counteract the host-induced iron deficiency, Mycma produces siderophores to capture iron. Mycma has two ferritins (encoded by mycma_0076 and mycma_0077) modulated by different iron concentrations, which allow the survival of this pathogen during iron scarcity. In this study, we constructed knockout (Mycma 0076KO) and complemented (Mycma 0076KOc) gene strains for mycma_0076 to understand the function of 0076 ferritin. Deletion of mycma_0076 in Mycma led to the transition in colony morphology from smooth to rough, alteration of the glycopeptidolipids spectra, increased permeability of the envelope, reduction in biofilm formation, increased susceptibility to antimicrobials and hydrogen peroxide-induced oxidative stress, and decreased internalization by macrophages. This study shows that Mycma_0076 ferritin in Mycma is involved in resistance to oxidative stress and antimicrobials, and alteration of cell envelope architecture. KEY POINTS: • Deletion of the mycma_0076 gene altered colony morphology to rough; • Mycma 0076KO changed GPL profile; • Absence of Mycma_0076 ferritin results in increased susceptibility to antimicrobials and oxidative stress in Mycma. Legend: a In wild-type M. abscessus subsp. massiliense strain, iron is captured from the environment by carboxymycobactins and mycobactins (1). Iron-dependent regulator (IdeR) proteins bind to ferrous iron (Fe⁺²) in the bacterial cytoplasm leading to the activation of the IdeR-Fe⁺² complex (2). The activated complex binds to the promoter regions of iron-dependent genes, called iron box, which in turn help in the recruitment of RNA polymerase to promote transcription of genes such as mycma_0076 and mycma_0077 ferritin genes (3). Mycma_0076 and Mycma_0077 ferritins bind to excess iron in the medium and promote Fe²⁺ oxidation into ferric iron (Fe³⁺) and store iron molecules to be released under iron scarcity conditions. (4) Genes related to biosynthesis and transport of glycopeptidolipids (GPL) are expressed normally and the cell envelope is composed of different GPL species (colored squares represented on the cell surface (GPLs). Consequently, WT Mycma present smooth colony phenotype (5). b In Mycma 0076KO strain, the lack of ferritin 0076 causes overexpression of mycma_0077 (6), but does not restore wild-type iron homeostasis and thus may result in free intracellular iron, even in the presence of miniferritins (MaDps). The excess iron potentiates oxidative stress (7) by generating hydroxyl radicals through Fenton Reaction. During this process, through an unknown mechanism, that could involve Lsr2 (8), the expression of GPL synthesis locus is regulated positively and/or negatively, resulting in alteration of GPL composition in the membrane (as represented by different colors of squares on the cell surface), resulting in a rough colony phenotype (9). The changes of GPL can increase cell wall permeability, contributing to antimicrobial susceptibility (10).

Omadacycline for the treatment of Mycobacterium abscessus infections: Case series and review of the literature

Treatment of Mycobacterium abscessus infections are problematic due to inherent multidrug resistance and lack of response to antibacterials commonly used as therapy for other mycobacterial infections. We report the clinical success of five patients who received definitive-treatment with an omadacycline-containing combination regimen for M. abscessus infection.

Treatment of Nontuberculous Mycobacterial (NTM) Pulmonary Infection in the US Bronchiectasis and NTM Registry: Treatment Patterns, Adverse Events, and Adherence to American Thoracic Society/Infectious Disease Society of America Treatment Guidelines

Among 1038 participants with pulmonary Mycobacterium avium complex and 120 with Mycobacterium abscessus enrolled in the US Bronchiectasis and NTM Research Registry, less than half received antibiotic therapy in the 24 months before registry enrollment, of which less than half were guideline based. Adverse effects occurred in 21% of therapy recipients, of whom 33% discontinued therapy.

Granulomatous infection of parotid gland and its subcutaneous tissue by Mycobacterium abscessus subspecies massiliense in a 3-year-old child

Acid fast bacilli positive granulomatous infections by non-tubrerculous mycobacteria are often misdiagnosed as tuberculosis. We present a case of parotid gland infection and abscess in the subcutaneous tissue over the gland which was suspected as tuberculosis by ultrasonogram and histopathology examinations. Mycobacterium abscessus subspecies massiliense was isolated and identified. In addition to the severe pulmonary infections, M.abscessus organism sometimes produces granulomatous reaction in extra pulmonary sites as the conventional anti tuberculous treatment is not useful, the correct identification is crucial for optimum management.

Noncanonical Mismatch Repair Protein NucS Modulates the Emergence of Antibiotic Resistance in Mycobacterium abscessus

NucS/EndoMS-dependent noncanonical mismatch repair (MMR) ensures the stability of genomic DNA in mycobacteria and acts as a guardian of the genome by preventing the accumulation of point mutations. In order to address whether the inactivation of noncanonical MMR could increase the acquisition of drug resistance by mutation, a ΔnucS strain was constructed and explored in the emerging pathogen Mycobacterium abscessus. Deletion of nucS resulted in a mutator phenotype with increased acquisition of resistance to macrolides and aminoglycosides, the two main groups of antimycobacterial agents for M. abscessus treatment, and also to second-line drugs such as fluoroquinolones. Inactivation of the noncanonical MMR in M. abscessus led to increases of 10- to 22-fold in the appearance of spontaneous mutants resistant to the macrolide clarithromycin and the aminoglycosides amikacin, gentamicin, and apramycin, compared with the wild-type strain. Furthermore, emergence of fluoroquinolone (ciprofloxacin) resistance was detected in a nucS-deficient strain but not in a wild-type M. abscessus strain. Acquired drug resistance to macrolides and aminoglycosides was analyzed through sequencing of the 23S rRNA gene rrl and the 16S rRNA gene rrs from independent drug-resistant colonies of both strains. When the acquisition of clarithromycin resistance was examined, a different mutational profile was detected in the M. abscessus ΔnucS strain compared with the wild-type one. To summarize, M. abscessus requires the NucS-dependent noncanonical MMR pathway to prevent the emergence of drug-resistant isolates by mutation. To our knowledge, this is the first report that reveals the role of NucS in a human pathogen, and these findings have potential implications for the treatment of M. abscessus infections. IMPORTANCE Chronic infections caused by M. abscessus are an emerging challenge in public health, posing a substantial health and economic burden, especially in patients with cystic fibrosis. Treatment of M. abscessus infections with antibiotics is particularly challenging, as its complex drug resistance mechanisms, including constitutive resistance through DNA mutation, lead to high rates of treatment failure. To decipher the evolution of antibiotic resistance in M. abscessus, we studied NucS-dependent noncanonical MMR, a unique DNA repair pathway involved in genomic maintenance. Inactivation of NucS is linked to the increase of DNA mutations (hypermutation), which can confer drug resistance. Our analysis detected increased acquisition of mutations conferring resistance to first-line and second-line antibiotics. We believe that this study will improve the knowledge of how this pathogen could evolve into an untreatable infectious agent, and it uncovers a role for hypermutators in chronic infectious diseases under antibiotic pressure.

In Vitro Profiling of the Synthetic RNA Polymerase Inhibitor MMV688845 against Mycobacterium abscessus

In a library screen of tuberculosis-active compounds for anti-Mycobacterium abscessus activity, we previously identified the synthetic phenylalanine amide MMV688845. In Mycobacterium tuberculosis, this class was shown to target the RpoB subunit of RNA polymerase, engaging a binding site distinct from that of the rifamycins. Due to its bactericidal activity, rifampicin is a key drug for the treatment of tuberculosis (TB). However, this natural product shows poor potency against M. abscessus due to enzymatic modification, and its clinical use is limited. Here, we carried out in vitro microbiological profiling of MMV688845 to determine its attractiveness as a substrate for a chemistry optimization project. MMV688845 was broadly active against the M. abscessus complex, displayed bactericidal against M. abscessus in vitro, and in a macrophage infection model showed additivity with commonly used anti-M. abscessus antibiotics and synergy with macrolides. Analyses of spontaneous resistant mutants mapped resistance to RpoB, confirming that MMV688845 has retained its target in M. abscessus. Together with its chemical tractability, the presented microbiological profiling reveals MMV688845 as an attractive starting point for hit-to-lead development to improve potency and to identify a lead compound with demonstrated oral in vivo efficacy. IMPORTANCE Infections with nontuberculous mycobacteria are an increasing health problem, and only a few new drug classes show activity against these multidrug-resistant bacteria. Due to insufficient therapy options, the development of new drug leads is necessary and should be advanced. The lead compound MMV688845, a substance active against M. abscessus complex, was characterized in depth. In various assays, it showed activity against M. abscessus, synergy with other antibiotics, and bactericidal effects.

Clofazimine as a comparator for preclinical efficacy evaluations of experimental therapeutics against pulmonary M. abscessus infection in mice

Mycobacteroides abscessus (Mab, also known as Mycobacterium abscessus) can cause chronic pulmonary disease in the setting of structural lung conditions. Current treatment recommendations require at least one year of daily therapy with repurposed antibiotics. Yet these therapies are often ineffective and associated with significant adverse events. To address this challenge, research efforts are underway to develop new antibiotics and regimens. During the preclinical phase of treatment development, experimental agents require testing and comparison alongside positive controls that are known agents with clinical history. As there are no FDA approved treatments for this indication, here, we have considered repurposed antibiotics currently included in the recommendation for treating Mab disease as candidates for selection of an ideal standard comparator that can serve as a positive control in preclinical studies. Clofazimine meets the criteria for an ideal positive control as it can be administered via the least invasive route, requires only once-daily dosing, is well tolerated, and is widely available in high purity from independent sources. Using a mouse model of pulmonary Mab disease, we assessed for ideal dosages of clofazimine in C3HeB/FeJ and BALB/c mice in a six-week treatment window. Clofazimine, 25 mg/kg, once daily, produced desired reduction in Mab burden in the lungs of C3HeB/FeJ and BALB/c mice. Based on these findings, we conclude that clofazimine meets the criteria for a positive control comparator in mice for use in preclinical efficacy assessments of agents for treatment of Mab pulmonary disease. Although not included in the current standard-of-care for treating Mab disease, rifabutin, 20 mg/kg, also produced desired reduction in Mab lung burden in C3HeB/FeJ mice but not in BALB/c mice. IMPORTANCE: Mycobacteroides abscessus can cause life-threatening infections in patients with chronic lung conditions. New treatments are needed as cure rate using existing drugs is low. During pre-clinical phase of treatment development, it is important to compare the efficacy of the experimental drug against existing ones with known history. Here, we demonstrate that clofazimine, one of the antibiotics repurposed for treating Mab disease, can serve as a positive control comparator for efficacy assessments of experimental drugs and regimens to treat M. abscessus disease in mice.

Rare extension of pancreatic pseudocyst with Mycobacterium abscessus into the iliopsoas muscle

Pancreatic pseudocyst is a well-known complication of both acute and chronic pancreatitis. Although extension into other anatomical sites is common, extension into the retrofascial space causing an iliopsoas abscess is exceedingly rare. Although its low incidence creates a diagnostic challenge for clinicians, early diagnosis is essential to prevent significant complications and poor patient outcomes. We present a case of iliopsoas abscess with unusual culture fluid growth in the setting of acute on chronic pancreatitis secondary to extension of a pancreatic pseudocyst. We also offer a brief review of the literature and pathophysiology of the condition.

In vitro synergy between manuka honey and amikacin against Mycobacterium abscessus complex shows potential for nebulisation therapy

Mycobacterium abscessusis an opportunistic human pathogen of increasing concern, due to its ability to cause aggressive pulmonary infections (especially in cystic fibrosis patients), as well as skin and soft tissue infections. M. abscessus is intrinsically drug resistant and treatment regimens are lengthy, consisting of multiple antibiotics with severe side effects and poor patient success rates. New and novel strategies are urgently required to combat these infections. One such strategy thus far overlooked for mycobacteria is manuka honey. For millennia manuka honey has been shown to have wide ranging medicinal properties, which have more recently been identified for its broad spectrum of antimicrobial activity. Here we demonstrate that manuka honey can be used to inhibit M. abscessus and a variety of drug resistant clinical isolates in vitro. We also demonstrate using a microbroth dilution checkerboard assay that manuka honey works synergistically with amikacin, which is one of the current front line antibiotics used for treatment of M. abscessus infections. This was further validated using an in vitro inhalation model, where we showed that with the addition of manuka honey, the amikacin dosage can be lowered whilst increasing its efficacy. These findings demonstrate the utility of manuka honey for incorporation into nebulised antibiotic treatment for respiratory infections, in particular M. abscessus. These results pave the way for a change of strategy for M. abscessus management, offering new therapeutic options for this deadly infection.

A Novel Leucyl-tRNA Synthetase Inhibitor, MRX-6038, Expresses Anti-Mycobacterium abscessus Activity In Vitro and In Vivo

Therapeutic options for Mycobacterium abscessus infections are extremely limited, and new drugs are needed. The anti-M. abscessus activity of MRX-6038, a new leucyl-tRNA synthetase inhibitor, was evaluated in vitro and in vivo. Antimicrobial susceptibility testing was performed on 12 nontuberculosis mycobacteria (NTM) reference strains and 227 clinical NTM isolates. A minimum bactericidal concentration assay was conducted to distinguish the bactericidal versus bacteriostatic activity of MRX-6038. The synergy between MRX-6038 and 12 clinically important antibiotics was determined using a checkerboard assay. The activity of MRX-6038 against M. abscessus residing inside macrophages was also evaluated. Finally, the potency of MRX-6038 in vivo was determined in a neutropenic mouse model that mimicked a pulmonary M. abscessus infection. MRX-6038 exhibited high anti-M. abscessus activity against extracellular M. abscessus in culture, with a MIC₅₀ of 0.063 mg/L and a MIC₉₀ of 0.125 mg/L. Fifty percent of the activity was bactericidal, and fifty percent was bacteriostatic. A synergy between MRX-6038 and clarithromycin or azithromycin was found in 25% of strains. No antagonism was evident between MRX-6038 and 12 antibiotics commonly used to treat NTM infections. MRX-6038 also exhibited activity against intracellular NTM, which caused a significant reduction in the bacterial load in the lungs of M. abscessus-infected neutropenic mice. In conclusion, MRX-6038 was active against M. abscessusin vitro and in vivo, and it represents a potential candidate for incorporation into strategies by which M. abscessus infections are treated.

Mycobacterium abscessus: insights from a bioinformatic perspective

Mycobacterium abscessus is a nontuberculous mycobacterium, associated with broncho-pulmonary infections in individuals suffering from cystic fibrosis, bronchiectasis, and pulmonary diseases. The risk factors for transmission include biofilms, contaminated water resources, fomites, and infected individuals. M. abscessus is extensively resistant to antibiotics. To date, there is no vaccine and combination antibiotic therapy is followed. However, drug toxicities, low cure rates, and high cost of treatment make it imperfect. Over the last 20 years, bioinformatic studies on M. abscessus have advanced our understanding of the pathogen. This review integrates knowledge from the analysis of genomes, microbiomes, genomic variations, phylogeny, proteome, transcriptome, secretome, antibiotic resistance, and vaccine design to further our understanding. The utility of genome-based studies in comprehending disease progression, surveillance, tracing transmission routes, and epidemiological outbreaks on a global scale has been highlighted. Furthermore, this review underlined the importance of using computational methodologies for pinpointing factors responsible for pathogen survival and resistance. We reiterate the significance of interdisciplinary research to fight M. abscessus. In a nutshell, the outcome of computational studies can go a long way in creating novel therapeutic avenues to control M. abscessus mediated pulmonary infections.

Transposon mutagenesis in Mycobacterium abscessus identifies an essential penicillin-binding protein involved in septal peptidoglycan synthesis and antibiotic sensitivity

Mycobacterium abscessus (Mab) is a rapidly growing non-tuberculous mycobacterium (NTM) that causes a wide range of infections. Treatment of Mab infections is difficult because the bacterium is intrinsically resistant to many classes of antibiotics. Developing new and effective treatments against Mab requires a better understanding of the unique vulnerabilities that can be targeted for future drug development. To achieve this, we identified essential genes in Mab by conducting transposon sequencing (TnSeq) on the reference Mab strain ATCC 19977. We generated ~51,000 unique transposon mutants and used this high-density library to identify 362 essential genes for in vitro growth. To investigate species-specific vulnerabilities in Mab, we further characterized MAB_3167c, a predicted penicillin-binding protein and hypothetical lipoprotein (PBP-lipo) that is essential in Mab and non-essential in Mycobacterium tuberculosis (Mtb). We found that PBP-lipo primarily localizes to the subpolar region and later to the septum as cells prepare to divide. Depletion of Mab PBP-lipo causes cells to elongate, develop ectopic branches, and form multiple septa. Knockdown of PBP-lipo along with PbpB, DacB1, and a carboxypeptidase, MAB_0519 lead to synergistic growth arrest. In contrast, these genetic interactions were absent in the Mtb model organism, Mycobacterium smegmatis, indicating that the PBP-lipo homologs in the two species exist in distinct genetic networks. Finally, repressing PBP-lipo sensitized the reference strain and 11 Mab clinical isolates to several classes of antibiotics, including the β-lactams, ampicillin, and amoxicillin by greater than 128-fold. Altogether, this study presents PBP-lipo as a key enzyme to study Mab-specific processes in cell wall synthesis and importantly positions PBP-lipo as an attractive drug target to treat Mab infections.

The Story of an Abscess: A Case of Mycobacterium abscessus Infection in an Immunocompetent Patient

Mycobacterium abscessus is a very unusual cause of infection in immunocompetent patients. It is a rapidly growing microbe that rarely causes disseminated infection or native valve endocarditis. This organism exhibits intrinsic and acquired resistance to multiple antibiotics and hence becomes a major issue in planning treatment regimens. We report a unique case of a young immunocompetent male patient presenting with stroke and persistent fever. After extensive investigations, he was found to have an abscess caused by M. abscessus in the sinus of Valsalva and thrombi in the aorta that was the sequelae following coronary angioplasty. This case report explains the difficulties in the diagnosis and treatment of M. abscessus.

In Mycobacterium abscessus, the stringent factor Rel regulates metabolism, but is not the only (p)ppGpp synthase

The stringent response is a broadly conserved stress response system that exhibits functional variability across bacterial clades. Here, we characterize the role of the stringent factor Rel in the non-tuberculous mycobacterial pathogen, Mycobacterium abscessus (Mab). We found that deletion of rel does not ablate (p)ppGpp synthesis, and that rel does not provide a survival advantage in several stress conditions, or in antibiotic treatment. Transcriptional data show that Rel_Mab is involved in regulating expression of anabolism and growth genes in stationary phase. However, it does not activate transcription of stress response or antibiotic resistance genes, and actually represses transcription of many antibiotic resistance genes. This work shows that there is an unannotated (p)ppGpp synthetase in Mab. Importance In this study, we examined the functional roles of the stringent factor Rel in Mycobacterium abscessus (Mab). In most species, stringent factors synthesize the alarmone (p)ppGpp, which globally alters transcription to promote growth arrest and survival under stress and in antibiotic treatment. Our work shows that in Mab, an emerging pathogen which is resistant to many antibiotics, the stringent factor Rel is not solely responsible for synthesizing (p)ppGpp. We find that Rel_Mab downregulates many metabolic genes under stress, but does not upregulate stress response genes and does not promote antibiotic tolerance. This study implies that there is another critical but unannotated (p)ppGpp synthetase in Mab, and suggests that Rel_Mab inhibitors are unlikely to sensitize Mab infections to antibiotic treatment.

Mycobacterium abscessus Genetic Determinants Associated with the Intrinsic Resistance to Antibiotics

Mycobacterium abscessus subsp. abscessus (MAB) is a fast-growing nontuberculous mycobacterium causing pulmonary infections in immunocompromised and immunocompetent individuals. The treatment of MAB infections in clinics is extremely challenging, as this organism is naturally resistant to most available antibiotics. There is limited knowledge on the mechanisms of MAB intrinsic resistance and on the genes that are involved in the tolerance to antimicrobials. To identify the MAB genetic factors, including the components of the cell surface transport systems related to the efflux pumps, major known elements contributing to antibiotic resistance, we screened the MAB transposon library of 2000 gene knockout mutants. The library was exposed at either minimal inhibitory (MIC) or bactericidal concentrations (BC) of amikacin, clarithromycin, or cefoxitin, and MAB susceptibility was determined through the optical density. The 98 susceptible and 36 resistant mutants that exhibited sensitivity below the MIC and resistance to BC, respectively, to all three drugs were sequenced, and 16 mutants were found to belong to surface transport systems, such as the efflux pumps, porins, and carrier membrane enzymes associated with different types of molecule transport. To establish the relevance of the identified transport systems to antibiotic tolerance, the gene expression levels of the export related genes were evaluated in nine MAB clinical isolates in the presence or absence of antibiotics. The selected mutants were also evaluated for their ability to form biofilms and for their intracellular survival in human macrophages. In this study, we identified numerous MAB genes that play an important role in the intrinsic mechanisms to antimicrobials and further demonstrated that, by targeting components of the drug efflux system, we can significantly increase the efficacy of the current antibiotics.

Successful treatment of rapid growing mycobacterial infections with source control alone: Case series

Rapid growing mycobacteria have been increasingly recognized as pathogens, both in immunocompromised and immunocompetent population, and their incidence has increased over the last decade significantly. Pulmonary infections are the most common, however, any organ can be affected. The treatment of these infections is costly, prolonged, and often antimicrobial resistance poses a significant challenge to a successful outcome. The source control together with antimicrobials is the cornerstone of treatment. We report a case series of 3 patients with extrapulmonary rapid growing mycobacterial infections in whom the successful treatment was achieved with source control alone.

Growth medium and nitric oxide alter Mycobacterium abscessus morphotype and virulence

Mycobacterium abscessus complex (MABC) infections cause significant morbidity and mortality among patients with chronic lung disease, like cystic fibrosis. MABC exists in smooth (S) and rough (R) morphotypes, but triggers of morphotype switching and associated pathogenicity or antimicrobial susceptibility are poorly understood. We demonstrate that M. abscessus subspecies abscessus (Mab), massiliense (Mms), and bolletii (Mbl) cultured in Middlebrook (MB) broth exhibit S morphotype, whereas the bacteria grown in Luria Bertani (LB) broth adopt the R morphotype, characterized by low glycopeptidolipid (GPL) expression. The components of broth that mediate this selection are complex, with albumin supplementation promoting growth of S morphotype, but not sufficient for complete selection. Consistent with the findings of other groups, R forms of Mab, Mms and Mbl selected by LB broth were internalized in RAW 264.7 macrophages with higher efficiency than S. Intracellular survival of broth-selected organisms was variable and was higher for S Mab, but lower for S Mms and Mbl. It is proposed that growth in R morphotype is induced during stress conditions, such as nutrient poor environments or during inflammation. One key component of inflammation is release of nitric oxide. We demonstrated that a nitric oxide donor (DETA-NONOate) appears to induce growth in an R morphotype, as indicated by reduced GPL expression of Mab. Mab treated with DETA-NONOate also enhanced susceptibility to azithromycin at sub-MIC concentrations. In conclusion, morphotype and macrophage intracellular bacterial load of MABC subspecies can be manipulated by growing the bacteria in different culture conditions. Nitric oxide may also drive morphotype selection and enhanced azithromycin activity against Mab and macrophage killing.

Mycobacterium abscessus Infection in Left Ventricular Assist Device (LVAD): A Case Series

The limited availability of donor organs worldwide, has provoked a surge in the need for implantable left ventricular assist devices (LVADs) mainly as a bridge to heart transplantation or destination therapy. The rate of complications from LVAD use is also increasing, impacting morbidity, mortality, and costs. LVAD infections due to nontuberculous mycobacteria (NTM) are exceedingly rare, yet very difficult to treat. Here we present three cases of Mycobacterium abscessus LVAD infections. To our knowledge, only two other cases have been documented.

Piperidine-4-Carboxamides Target DNA Gyrase in Mycobacterium abscessus

New, more-effective drugs for the treatment of lung disease caused by nontuberculous mycobacteria (NTM) are needed. Among NTM opportunistic pathogens, Mycobacterium abscessus is the most difficult to cure and intrinsically multidrug resistant. In a whole-cell screen of a compound collection active against Mycobacterium tuberculosis, we previously identified the piperidine-4-carboxamide (P4C) MMV688844 (844) as a hit against M. abscessus. Here, we identified a more potent analog of 844 and showed that both the parent and improved analog retain activity against strains representing all three subspecies of the M. abscessus complex. Furthermore, P4Cs showed bactericidal and antibiofilm activity. Spontaneous resistance against the P4Cs emerged at a frequency of 10⁻⁸/CFU and mapped to gyrA and gyrB encoding the subunits of DNA gyrase. Biochemical studies with recombinant M. abscessus DNA gyrase showed that P4Cs inhibit the wild-type enzyme but not the P4C-resistant mutant. P4C-resistant strains showed limited cross-resistance to the fluoroquinolone moxifloxacin, which is in clinical use for the treatment of macrolide-resistant M. abscessus disease, and no cross-resistance to the benzimidazole SPR719, a novel DNA gyrase inhibitor in clinical development for the treatment of mycobacterial diseases. Analyses of P4Cs in recA promoter-based DNA damage reporter strains showed induction of recA promoter activity in the wild type but not in the P4C-resistant mutant background. This indicates that P4Cs, similar to fluoroquinolones, cause DNA gyrase-mediated DNA damage. Together, our results show that P4Cs present a novel class of mycobacterial DNA gyrase inhibitors with attractive antimicrobial activities against the M. abscessus complex.

Rifampicin-Liposomes for Mycobacterium abscessus Infection Treatment: Intracellular Uptake and Antibacterial Activity Evaluation

Treatment of pulmonary infections caused by Mycobacterium abscessus are extremely difficult to treat, as this species is naturally resistant to many common antibiotics. Liposomes are vesicular nanocarriers suitable for hydrophilic and lipophilic drug loading, able to deliver drugs to the target site, and successfully used in different pharmaceutical applications. Moreover, liposomes are biocompatible, biodegradable and nontoxic vesicles and nebulized liposomes are efficient in targeting antibacterial agents to macrophages. The present aim was to formulate rifampicin-loaded liposomes (RIF-Lipo) for lung delivery, in order to increase the local concentration of the antibiotic. Unilamellar liposomal vesicles composed of anionic DPPG mixed with HSPC for rifampicin delivery were designed, prepared, and characterized. Samples were prepared by using the thin-film hydration method. RIF-Lipo and unloaded liposomes were characterized in terms of size, ζ-potential, bilayer features, stability and in different biological media. Rifampicin's entrapment efficiency and release were also evaluated. Finally, biological activity of RIF-loaded liposomes in Mycobacterium abscessus-infected macrophages was investigated. The results show that RIF-lipo induce a significantly better reduction of intracellular Mycobacterium abscessus viability than the treatment with free drug. Liposome formulation of rifampicin may represent a valuable strategy to enhance the biological activity of the drug against intracellular mycobacteria.

Disseminated Mycobacterium abscessus subspecies massiliense infection and subsequent prosthetic joint infection in a hemodialysis patient: A case report

A 74-year-old man with diabetic nephropathy undergoing dialysis after total knee arthroplasty presented to our hospital with dyspnea and abnormal behavior such as wearing his pants on his head. The patient was in shock with ventricular tachycardia. Urine and blood cultures showed MAM with sterile pyuria. We administered amikacin and imipenem cilastatin, but repeated cultures were persistently positive. Although we initially chose not to administer azithromycin because of a higher risk of fatal arrhythmia, we had no choice but to administer azithromycin because of treatment failure. Upon close monitoring, we observed no arrhythmia, and the blood cultures became negative. The patient was discharged on day 106 without any symptoms. However, 2 months after discontinuation of antibiotics, he was readmitted and diagnosed with prosthetic joint infection due to MAM. He could not undergo total knee arthroplasty resection because of his low tolerance to surgery. We re-administered same antibiotics, and repeated draining and cleaning of his left knee for several weeks. The inflammation in the knee joint gradually improved, and the patient was discharged while treatment with azithromycin and amikacin was continued. After being discharged, the patient did not experience recurrent disease for at least 6 months. Our case suggests that MAM can cause sterile pyuria and infection in a patient with diabetic nephropathy. The macrolide agent is a key drug for MAM infection, and repeated joint lavage in addition to administering antibiotics may be an alternative treatment for prosthetic joint infection in patients with intolerance to surgery.

Invasive Mycobacterium abscessus Complex Infection After Cardiac Surgery: Epidemiology, Management, and Clinical Outcomes

BACKGROUND

We recently mitigated a clonal outbreak of hospital-acquired Mycobacterium abscessus complex (MABC), which included a large cluster of adult patients who developed invasive infection after exposure to heater-cooler units during cardiac surgery. Recent studies have detailed Mycobacterium chimaera infections acquired during cardiac surgery; however, little is known about the epidemiology and clinical courses of cardiac surgery patients with invasive MABC infection.

METHODS

We retrospectively collected clinical data on all patients who underwent cardiac surgery at our hospital and subsequently had positive cultures for MABC from 2013 through 2016. Patients with ventricular assist devices or heart transplants were excluded. We analyzed patient characteristics, antimicrobial therapy, surgical interventions, and clinical outcomes.

RESULTS

Ten cardiac surgery patients developed invasive, extrapulmonary infection from M. abscessus subspecies abscessus in an outbreak setting. Median time from presumed inoculation in the operating room to first positive culture was 53 days (interquartile range [IQR], 38-139 days). Disseminated infection was common, and the most frequent culture-positive sites were mediastinum (n = 7) and blood (n = 7). Patients received a median of 24 weeks (IQR, 5-33 weeks) of combination antimicrobial therapy that included multiple intravenous agents. Six patients required antibiotic changes due to adverse events attributed to amikacin, linezolid, or tigecycline. Eight patients underwent surgical management, and 6 patients required multiple sternal debridements. Eight patients died within 2 years of diagnosis, including 4 deaths directly attributable to MABC infection.

CONCLUSIONS

Despite aggressive medical and surgical management, invasive MABC infection after cardiac surgery caused substantial morbidity and mortality. New treatment strategies are needed, and compliance with infection prevention guidelines remains critical.

First Penicillin-Binding Protein Occupancy Patterns for 15 β-Lactams and β-Lactamase Inhibitors in Mycobacterium abscessus

Mycobacterium abscessus causes serious infections that often require over 18 months of antibiotic combination therapy. There is no standard regimen for the treatment of M. abscessus infections, and the multitude of combinations that have been used clinically have had low success rates and high rates of toxicities. With β-lactam antibiotics being safe, double β-lactam and β-lactam/β-lactamase inhibitor combinations are of interest for improving the treatment of M. abscessus infections and minimizing toxicity. However, a mechanistic approach for building these combinations is lacking since little is known about which penicillin-binding protein (PBP) target receptors are inactivated by different β-lactams in M. abscessus We determined the preferred PBP targets of 13 β-lactams and 2 β-lactamase inhibitors in two M. abscessus strains and identified PBP sequences by proteomics. The Bocillin FL binding assay was used to determine the β-lactam concentrations that half-maximally inhibited Bocillin binding (50% inhibitory concentrations [IC₅₀s]). Principal component analysis identified four clusters of PBP occupancy patterns. Carbapenems inactivated all PBPs at low concentrations (0.016 to 0.5 mg/liter) (cluster 1). Cephalosporins (cluster 2) inactivated PonA2, PonA1, and PbpA at low (0.031 to 1 mg/liter) (ceftriaxone and cefotaxime) or intermediate (0.35 to 16 mg/liter) (ceftazidime and cefoxitin) concentrations. Sulbactam, aztreonam, carumonam, mecillinam, and avibactam (cluster 3) inactivated the same PBPs as cephalosporins but required higher concentrations. Other penicillins (cluster 4) specifically targeted PbpA at 2 to 16 mg/liter. Carbapenems, ceftriaxone, and cefotaxime were the most promising β-lactams since they inactivated most or all PBPs at clinically relevant concentrations. These first PBP occupancy patterns in M. abscessus provide a mechanistic foundation for selecting and optimizing safe and effective combination therapies with β-lactams.

A real-time PCR assay for rapid identification of inducible and acquired clarithromycin resistance in Mycobacterium abscessus

BACKGROUND

Mycobacterium abscessus is a rapidly growing mycobacteria involved in severe infections of the lung, skin, or soft tissue. Macrolides such as clarithromycin are the recommended first line drugs for treatment of M. abscessus infections. However, M. abscessus has dual mechanisms of resistance to macrolides, making treatment by macrolides difficult. A functional erm(41) gene confers for inducible resistance while acquired mutations on the 23S rRNA rrl gene confer for constitutive resistance.

METHODS

We have developed a real-time PCR assay to detect both inducible and acquired resistance to clarithromycin, and compared the results to traditional erm(41) and rrl sequencing and phenotypic susceptibility testing using Sensititre™ plates.

RESULTS

Of the total 126 M. abscessus isolates tested, truncated erm(41) was found in 23/126 (18.3%) of the samples, 27/126 (21.4%) had a T28C mutation in erm(41), and 2/126 (1.6%) had an acquired A2058C mutation in rrl. The phenotypic results correlated with the expected sequencing results in 121/126 samples (96%). Phenotypic testing compared to real-time PCR resolved 2 of these discrepancies by showing the existence of both erm(41) alleles in the isolates that sequencing missed. One culture was found to be mixed with two M. abscessus subsp. as per hsp65 sequencing and 2 isolates had discordance between molecular and phenotypic results. It was presumed that 3 isolates showed discrepancy between sequencing and real-time PCR, but one culture was mixed and other 2 detected both alleles by real-time PCR leading to 100% concordance when compared to sequencing.

CONCLUSION

In conclusion, real-time PCR is more accurate for detection of both acquired and induced clarithromycin resistance, specifically when mixed genic profiles are present in a sample.

Effect of Coptis chinensis on Biofilm Formation and Antibiotic Susceptibility in Mycobacterium abscessus

Mycobacterium abscessus infections are notoriously difficult to be treated and newer treatment options are required. Coptis chinensis (C. chinensis) and its main compound berberine are frequently used to treat bacterial and viral infections. In this study, the susceptibility of M. abscessus to C. chinensis extract and berberine was assessed by minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) evaluation. The effects of C. chinensis and berberine on biofilm formation and antibiotic susceptibility in M. abscessus were observed. C. chinensis at concentrations of MIC (1.5 mg/mL) and 2 × MIC (3.0 mg/mL) and berberine at ½ × MIC (0.125 mg/mL) demonstrated a strong inhibition of biofilm formation. Concentration of C. chinensis at ½ × MIC resulted in a significant reduction in MICs of trimethoprim/sulfamethoxazole (TMP/SXT), clarithromycin (CLA), and linezolid (LZD). Similarly, ½ × MIC berberine had a significant effect on the MIC reductions of nine antibiotics including TMP/SXT, CLA, and LZD. Notably, the resistance level MIC of LZD against M. abscessus was reversed to a susceptible level by treatment with either C. chinensis or berberine. Therefore, C. chinensis and berberine have the potential to produce a synergistic antimycobacterial effect, reduce biofilm formation, and decrease antibacterial resistance to LZD in M. abscessus.

The synergetic effect of Imipenem-clarithromycin combination in the Mycobacteroides abscessus complex

Background

Nontuberculous mycobacteria (NTM) are ubiquitous organisms and the incidence of NTM infections has been increasing in recent years. Mycobacteroides abscessus (M. abscessus) is one of the most antimicrobial-resistant NTM; however, no reliable antibiotic regimen can be officially advocated. We evaluated the efficacy of clarithromycin in combination with various antimicrobial agents against the M. abscessus complex.

Results

Twenty-nine clinical strains of M. abscessus were isolated from various clinical samples. Of the isolates, 10 (34.5%) were of M. abscessus subsp. abscessus, 18 (62.1%) of M. abscessus subsp. massiliense, and 1 (3.4%) of M. abscessus subsp. bolletii. MICs of three antimicrobial agents (amikacin, imipenem, and moxifloxacin) were measured with or without clarithromycin. The imipenem-clarithromycin combination significantly reduced MICs compared to clarithromycin and imipenem monotherapies, including against resistant strains. The association between susceptibility of the M. abscessus complex and each combination of agents was significant (p = 0.001). Adjusted residuals indicated that the imipenem-clarithromycin combination had the synergistic effect (adjusted residual = 3.1) and suppressed the antagonistic effect (adjusted residual = − 3.1). In subspecies of M. abscessus complex, the association with susceptibility of M. abscessus subsp. massiliense was similarly statistically significant (p = 0.036: adjusted residuals of synergistic and antagonistic effect respectively: 2.6 and − 2.6). The association with susceptibility of M. abscessus subsp. abscessus also showed a similar trend but did not reach statistical significance.

Conclusion

Our data suggest that the imipenem-clarithromycin combination could be the recommended therapeutic choice for the treatment of M. abscessus complex owing to its ability to restore antimicrobial susceptibility.

Safety and Tolerability of Clofazimine in a Cohort of Children With Odontogenic Mycobacterium abscessus Infection

Mycobacterium abscessus infections can be challenging to treat. Clofazimine has excellent in vitro activity against M abscessus, but reports of its use, particularly in children, have been limited. In this study, clofazimine was given to 27 children during an outbreak of odontogenic mycobacterial infections and seemed to be well tolerated as part of a multidrug regimen.

Omadacycline for the Treatment of Mycobacterium abscessus Disease: A Case Series

Background

Omadacycline is an aminomethylcycline antimicrobial approved by the US Food and Drug Administration in 2018 for community-acquired bacterial pneumonia and acute bacterial skin and skin structure infections. It has in vitro activity against nontuberculous mycobacteria, including Mycobacterium abscessus complex, but clinical data for this indication are lacking.

Methods

Omadacycline use was reviewed at an 804-bed academic medical center. Patients were included if they received omadacycline for culture-proven M abscessus disease in 2019.

Results

Four patients received omadacycline for the treatment of culture-positive M abscessus disease in 2019. Two patients had cutaneous disease, 1 had pulmonary disease, and 1 had osteomyelitis and bacteremia. The patients received omadacycline for a median duration of 166 days (range, 104-227) along with a combination of other antimicrobial agents. Omadacycline-containing regimens were associated with a clinical cure in 3 of 4 patients, with 1 patient improving on ongoing treatment. Omadacycline's tolerability was acceptable for patients with M abscessus disease, with 1 patient discontinuing therapy in month 6 due to nausea.

Conclusions

Omadacycline is a novel oral option for the treatment of M abscessus disease, for which safe and effective options are needed. Although this case series is promising, further data are required to determine omadacycline's definitive role in the treatment of M abscessus disease.

Treatment of Nontuberculous Mycobacterial Pulmonary Disease: An Official ATS/ERS/ESCMID/IDSA Clinical Practice Guideline

Nontuberculous mycobacteria (NTM) represent over 190 species and subspecies, some of which can produce disease in humans of all ages and can affect both pulmonary and extrapulmonary sites. This guideline focuses on pulmonary disease in adults (without cystic fibrosis or human immunodeficiency virus infection) caused by the most common NTM pathogens such as Mycobacterium avium complex, Mycobacterium kansasii, and Mycobacterium xenopi among the slowly growing NTM and Mycobacterium abscessus among the rapidly growing NTM. A panel of experts was carefully selected by leading international respiratory medicine and infectious diseases societies (ATS, ERS, ESCMID, IDSA) and included specialists in pulmonary medicine, infectious diseases and clinical microbiology, laboratory medicine, and patient advocacy. Systematic reviews were conducted around each of 22 PICO (Population, Intervention, Comparator, Outcome) questions and the recommendations were formulated, written, and graded using the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach. Thirty-one evidence-based recommendations about treatment of NTM pulmonary disease are provided. This guideline is intended for use by healthcare professionals who care for patients with NTM pulmonary disease, including specialists in infectious diseases and pulmonary diseases.

Efficacy and Mechanisms of Flavonoids against the Emerging Opportunistic Nontuberculous Mycobacteria

Nontuberculous mycobacteria (NTM) are the causative agent of severe chronic pulmonary diseases and is accountable for post-traumatic wound infections, lymphadenitis, endometritis, cutaneous, eye infections and disseminated diseases. These infections are extremely challenging to treat due to multidrug resistance, which encompasses the classical and existing antituberculosis agents. Hence, current studies are aimed to appraise the antimycobacterial activity of flavonoids against NTM, their capacity to synergize with pharmacological agents and their ability to block virulence. Flavonoids have potential antimycobacterial effects at minor quantities by themselves or in synergistic combinations. A cocktail of flavonoids used with existing antimycobacterial agents is a strategy to lessen side effects. The present review focuses on recent studies on naturally occurring flavonoids and their antimycobacterial effects, underlying mechanisms and synergistic effects in a cocktail with traditional agents.

Treatment of nontuberculous mycobacterial pulmonary disease: an official ATS/ERS/ESCMID/IDSA clinical practice guideline

Nontuberculous mycobacteria (NTM) represent over 190 species and subspecies, some of which can produce disease in humans of all ages and can affect both pulmonary and extrapulmonary sites. This guideline focuses on pulmonary disease in adults (without cystic fibrosis or human immunodeficiency virus infection) caused by the most common NTM pathogens such as Mycobacterium avium complex, Mycobacterium kansasii, and Mycobacterium xenopi among the slowly growing NTM and Mycobacterium abscessus among the rapidly growing NTM. A panel of experts was carefully selected by leading international respiratory medicine and infectious diseases societies (ATS, ERS, ESCMID, IDSA) and included specialists in pulmonary medicine, infectious diseases and clinical microbiology, laboratory medicine, and patient advocacy. Systematic reviews were conducted around each of 22 PICO (Population, Intervention, Comparator, Outcome) questions and the recommendations were formulated, written, and graded using the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach. Thirty-one evidence-based recommendations about treatment of NTM pulmonary disease are provided. This guideline is intended for use by healthcare professionals who care for patients with NTM pulmonary disease, including specialists in infectious diseases and pulmonary diseases.

Spontaneous sputum conversion and reversion in Mycobacterium abscessus complex lung disease

Background

We aim to investigate the rate of spontaneous sputum conversion and reversion in patients with Mycobacterium abscessus complex (MABC) lung disease.

Methods

Among 241 patients diagnosed with MABC lung disease between July 2012 and December 2018, 126 patients with persistent sputum positivity for ≥ 6 months without treatment were enrolled at a tertiary referral center in South Korea. Patients were subdivided into two groups, depending on whether or not treatment was initiated within 2 years of diagnosis. The rates of spontaneous sputum culture conversion and reversion was investigated in patients who did not receive treatment within 2 years.

Results

The mean age of 126 patients was 62.9 years. During a mean follow-up duration of 3.2 years, 33 (26.2%) patients received treatment within 2 years of diagnosis. Among the remaining 93 patients not receiving treatment within 2 years, spontaneous sputum conversion occurred in 24 (25.8%) patients during a mean follow-up duration of 3.7 years after diagnosis. No significant differences were observed in time to conversion between Mycobacterium abscessus and Mycobacterium massiliense lung diseases. The Cox regression analysis showed that malignancy as a comorbid disease and the lower number of lobes involved were independent predictors of spontaneous sputum conversion. After spontaneous sputum conversion, reversion occurred in 27.8% patients at a median of 18.2 months after conversion.

Conclusions

Among patients with MABC lung disease who did not receive treatment for at least 2 years after diagnosis, approximately one-fourth experienced spontaneous conversion. However, not a few patients experienced reversion after spontaneous conversion.

Thiostrepton: A Novel Therapeutic Drug Candidate for Mycobacterium abscessus Infection

Mycobacterium abscessus is a rapid-growing, multidrug-resistant, non-tuberculous mycobacterial species responsible for a variety of human infections, such as cutaneous and pulmonary infections. M. abscessus infections are very difficult to eradicate due to the natural and acquired multidrug resistance profiles of M. abscessus. Thus, there is an urgent need for the development of effective drugs or regimens against M. abscessus infections. Here, we report the activity of a US Food and Drug Administration approved drug, thiostrepton, against M. abscessus. We found that thiostrepton significantly inhibited the growth of M. abscessus wild-type strains, subspecies, clinical isolates, and drug-resistant mutants in vitro and in macrophages. In addition, treatment of macrophages with thiostrepton significantly decreased proinflammatory cytokine production in a dose-dependent manner, suggesting an inhibitory effect of thiostrepton on inflammation induced during M. abscessus infection. We further showed that thiostrepton exhibits antimicrobial effects in vivo using a zebrafish model of M. abscessus infection.

PLGA nanocapsules improve the delivery of clarithromycin to kill intracellular Staphylococcus aureus and Mycobacterium abscessus

Drug delivery systems are promising for targeting antibiotics directly to infected tissues. To reach intracellular Staphylococcus aureus and Mycobacterium abscessus, we encapsulated clarithromycin in PLGA nanocapsules, suitable for aerosol delivery by nebulization of an aqueous dispersion. Compared to the same dose of free clarithromycin, nanoencapsulation reduced 1000 times the number of intracellular S. aureus in vitro. In RAW cells, while untreated S. aureus was located in acidic compartments, the treated ones were mostly situated in non-acidic compartments. Clarithromycin-nanocapsules were also effective against M. abscessus (70-80% killing efficacy). The activity of clarithromycin-nanocapsules against S. aureus was also confirmed in vivo, using a murine wound model as well as in zebrafish. The permeability of clarithromycin-nanocapsules across Calu-3 monolayers increased in comparison to the free drug, suggesting an improved delivery to sub-epithelial tissues. Thus, clarithromycin-nanocapsules are a promising strategy to target intracellular S. aureus and M. abscessus.

Crystal structure of the aminoglycosides N-acetyltransferase Eis2 from Mycobacterium abscessus

Mycobacterium abscessus is an emerging human pathogen that is notorious for being one of the most drug-resistant species of Mycobacterium. It has developed numerous strategies to overcome the antibiotic stress response, limiting treatment options and leading to frequent therapeutic failure. The panel of aminoglycosides (AG) usually used in the treatment of M. abscessus pulmonary infections is restricted by chemical modification of the drugs by the N-acetyltransferase Eis2 protein (Mabs_Eis2). This enzyme acetylates the primary amine of AGs, preventing these antibiotics from binding ribosomal RNA and thereby impairing their activity. In this study, the high-resolution crystal structures of Mabs_Eis2 in its apo- and cofactor-bound forms were solved. The structural analysis of Mabs_Eis2, supported by the kinetic characterization of the enzyme, highlights the large substrate specificity of the enzyme. Furthermore, in silico docking and biochemical approaches attest that Mabs_Eis2 modifies clinically relevant drugs such as kanamycin and amikacin, with a better efficacy for the latter. In line with previous biochemical and in vivo studies, our work suggests that Mabs_Eis2 represents an attractive pharmacological target to be further explored. The high-resolution crystal structures presented here may pave the way to the design of Eis2-specific inhibitors with the potential to counteract the intrinsic resistance levels of M. abscessus to an important class of clinically important antibiotics. DATABASE: Structural data are available in the PDB database under the accession numbers: 6RFY, 6RFX and 6RFT.

Improved Clinical Outcome After Treatment of Mycobacterium abscessus Complex Pulmonary Disease in Children With Cystic Fibrosis

BACKGROUND

Mycobacterium abscessus complex pulmonary disease (M. abscessus PD) in cystic fibrosis (CF) is challenging to treat. Current guideline therapeutic regimens involving an intensive phase of intravenous (IV) antibiotics followed by a consolidation phase of inhaled and oral antibiotics are not evidence-based. The objectives of this study were to characterize the clinical outcomes and clearance of Mycobacterium abscessus complex (M. abscessus) from respiratory cultures in children with CF M. abscessus PD.

METHODS

This retrospective longitudinal cohort analysis evaluated the first course of treatment for M. abscessus PD in 33 children in Queensland, Australia between 2001 and 2015. Spirometry and nutritional outcomes 2 years pretreatment and 1 year posttreatment were compared with clearance or relapse/persistence of Mycobacterium abscessus complex from respiratory cultures.

RESULTS

Nine of 18 children who completed therapy, cleared infection. Three of 7 children who completed only intensive therapy cleared sputum compared with 0/8 children who did not. The trajectory of the percent predicted forced expiratory volume in 1 s and age standardized body mass index significantly improved posttreatment in those that cleared sputum (P < 0.0001).

CONCLUSIONS

These results suggest that current treatment recommendations for M. abscessus PD are associated with some success in clearing infection in children with CF and improvement in lung function and body mass index. Clinical trials are required to determine the best treatment approaches.

Top Questions in the Diagnosis and Treatment of Pulmonary M. abscessus Disease

Mycobacterium abscessus disease is particularly challenging to treat, given the intrinsic drug resistance of this species and the limited data on which recommendations are based, resulting in a greater reliance on expert opinion. We address several commonly encountered questions and management considerations regarding pulmonary Mycobacterium abscessus disease, including the role of subspecies identification, diagnostic criteria for determining disease, interpretation of drug susceptibility test results, approach to therapy including the need for parenteral antibiotics and the role for new and repurposed drugs, and the use of adjunctive strategies such as airway clearance and surgical resection.