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

Sources, transmission and hospital-associated outbreaks of nontuberculous mycobacteria: a review

Nontuberculous mycobacteria (NTM) are widespread environmental organisms found in both natural and man-made settings, such as building plumbing, water distribution networks and hospital water systems. Their ubiquitous presence increases the risk of transmission, leading to a wide range of human infections, particularly in immunocompromised individuals. NTM primarily spreads through environmental exposures, such as inhaling aerosolized particles, ingesting contaminated food and introducing it into wounds. Hospital-associated outbreaks have been linked to contaminated medical devices and water systems. Furthermore, the rising global incidence, prevalence and isolation rates highlight the urgency of addressing NTM infections. Gaining a thorough insight into the sources and epidemiology of NTM infection is crucial for devising novel strategies to prevent and manage NTM transmission and infections.

Identification of Mycobacterium abscessus using the peaks of ribosomal protein L29, L30 and hemophore-related protein by MALDI-MS proteotyping

Mycobacteroides (Mycobacterium) abscessus, which causes a variety of infectious diseases in humans, is becoming detected more frequently in clinical specimens as cases are spreading worldwide. Taxonomically, M. abscessus is composed of three subspecies of M. abscessus subsp. abscessus, M. abscessus subsp. bolletii, and M. abscessus subsp. massiliense, with different susceptibilities to macrolides. In order to identify rapidly these three subspecies, we determined useful biomarker proteins, including ribosomal protein L29, L30, and hemophore-related protein, for distinguishing the subspecies of M. abscessus using the matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) profiles. Thirty-three clinical strains of M. abscessus were correctly identified at the subspecies-level by the three biomarker protein peaks. This study ultimately demonstrates the potential of routine MALDI-MS-based laboratory methods for early identification and treatment for M. abscessus infections.

In vitro activity of cefoxitin, imipenem, meropenem, and ceftaroline in combination with vaborbactam against Mycobacterium abscessus

Mycobacterium abscessus (MAB) infections pose a growing public health threat. Here, we assessed the in vitro activity of the boronic acid-based β-lactamase inhibitor, vaborbactam, with different β-lactams against 100 clinical MAB isolates. Enhanced activity was observed with meropenem and ceftaroline with vaborbactam (1- and >4-fold MIC50/90 reduction). CRISPRi-mediated blaMAB gene knockdown showed a fourfold MIC reduction to ceftaroline but not the other β-lactams. Our findings demonstrate vaborbactam's potential in combination therapy against MAB infections.

Cervical lymphadenitis from Mycobacterium avium complex

We present an instructive case of cervical lymphadenitis in a young man without a history of HIV infection. The patient developed spontaneous left-sided neck swelling that progressed over 4 months. CT imaging demonstrated a necrotic left-sided neck mass within the cervical lymph node chain. He was initially prescribed azithromycin and rifampin for presumed cat scratch disease with improvement but incomplete resolution of symptoms. Blood cultures ordered 2 months later grew Mycobacterium avium complex (MAC) and the patient had an excellent clinical response to MAC therapy. Here, we review the case, including presentation and management, and describe the implications for the immune status of the host and long-term considerations for treatment.

Impact of Mycobacteroides abscessus colony morphology on biofilm formation and antimicrobial resistance

Mycobacteroides abscessus is one of the most resistant bacteria so far known and causes severe and hard to treat lung infections in predisposed patients such as those with Cystic Fibrosis (CF). Further, it causes nosocomial infections by forming biofilms on medical devices or water reservoirs. An eye-catching feature of M. abscessus is the growth in two colony morphotypes. Depending on the presence or absence of glycopeptidolipids on the cell surface, it forms smooth or rough colonies. In this study, a porous glass bead biofilm model was used to compare biofilm formation, biofilm organization and biofilm matrix composition in addition to the antimicrobial susceptibility of M. abscessus biofilms versus suspensions of isogenic (smooth and rough) patient isolates. Both morphotypes reached the same cell densities in biofilms. The biofilm architecture, however, was dramatically different with evenly distributed oligo-layered biofilms in smooth isolates, compared to tightly packed, voluminous biofilm clusters in rough morphotypes. Biofilms of both morphotypes contained more total biomass of the matrix components protein, lipid plus DNA than was seen in corresponding suspensions. The biofilm mode of growth of M. abscessus substantially increased resistance to the antibiotics amikacin and tigecycline. Tolerance to the disinfectant peracetic acid of both morphotypes was increased when grown as biofilm, while tolerance to glutaraldehyde was significantly increased in biofilm of smooth isolates only. Overall, smooth colony morphotypes had more pronounced antimicrobial resistance benefit when growing as biofilm than M. abscessus showing rough colony morphotypes.

Isoegomaketone exhibits potential as a new Mycobacterium abscessus inhibitor

Although the incidence of Mycobacterium abscessus infection has recently increased significantly, treatment is difficult because this bacterium is resistant to most anti-tuberculosis drugs. In particular, M. abscessus is often resistant to available macrolide antibiotics, so therapeutic options are extremely limited. Hence, there is a pressing demand to create effective drugs or therapeutic regimens for M. abscessus infections. The aim of the investigation was to assess the capability of isoegomaketone (iEMK) as a therapeutic option for treating M. abscessus infections. We determined the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of iEMK for both reference and clinically isolated M. abscessus strains. In addition to time-kill and biofilm formation assays, we evaluated iEMK's capability to inhibit M. abscessus growth in macrophages using an intracellular colony counting assay. iEMK inhibited the growth of reference and clinically isolated M. abscessus strains in macrophages and demonstrated effectiveness at lower concentrations against macrophage-infected M. abscessus than when used to treat the bacteria directly. Importantly, iEMK also exhibited anti-biofilm properties and the potential to mitigate macrolide-inducible resistance, underscoring its promise as a standalone or adjunctive therapeutic agent. Overall, our results suggest that further development of iEMK as a clinical drug candidate is promising for inhibiting M. abscessus growth, especially considering its dual action against both planktonic bacteria and biofilms.

Phylogenetic distribution of malonate semialdehyde decarboxylase (MSAD) genes among strains within the genus Mycobacterium: evidence of MSAD gene loss in the evolution of pathogenic mycobacteria

Despite the great diversity of malonate semialdehyde decarboxylases (MSADs), one of five subgroups of the tautomerase superfamily (TSF) found throughout the biosphere, their distribution among strains within the genus Mycobacterium remains unknown. In this study, we sought to investigate the phylogenetic distribution of MSAD genes of mycobacterial species via genome analysis of 192 different reference Mycobacterium species or subspecies retrieved from NCBI databases. We found that in a total of 87 of 192 strains (45.3%), MSAD-1 and MSAD-2 were distributed in an exclusive manner among Mycobacterium species except for 12 strains, including Mycobacterium chelonae members, with both in their genome. Of note, Mycobacterium strains better adapted to the host and of high virulence potential, such as the Mycobacterium tuberculosis complex, Mycobacterium leprae, Mycobacterium marinum, Mycobacterium ulcerans, and Mycobacterium avium subsp. paratuberculosis, had no orthologs of MSAD in their genome, suggesting MSAD loss during species differentiation in pathogenic slow-growing Mycobacterium. To investigate the MSAD distribution among strains of M. avium subspecies, the genome sequences of a total of 255 reference strains from the four subspecies of M. avium (43 of subspecies avium, 162 of subspecies hominissuis, 49 of subspecies paratuberculosis, and 1 of subspecies silvaticum) were further analyzed. We found that only 121 of 255 strains (47.4%) had MSADs in their genome, with none of the 49 M. avium subsp. paratuberculosis strains having MSAD genes. Even in 13 of 121 M. avium strains with the MSAD-1 gene in their genome, deletion mutations in the 98th codon causing premature termination of MSAD were found, further highlighting the occurrence of MSAD pseudogenization during species or subspecies differentiation of M. avium. In conclusion, our data indicated that there are two distinct types of MSADs, MSAD-1 and MSAD-2, among strains in the Mycobacterium genus, but more than half of the strains, including pathogenic mycobacteria, M. tuberculosis and M. leprae, have no orthologs in their genome, suggesting MSAD loss during host adaptation of pathogenic mycobacteria. In the future, the role of two distinct MSADs, MSAD-1 and MSAD-2, in mycobacterial pathogenesis or evolution should be investigated.

Investigating bacterial infections in Galleria mellonella larvae: Insights into pathogen dissemination and behavior

The insect Galleria mellonella is an alternative animal model widely used for studying bacterial infections. It presents a wide range of advantages, including its low cost, easy maintenance and lack of ethical constraints. Among other features, their innate immune system is very similar to that of mammals. In this study, we dissected several larvae infected with important human pathogens: Mycobacterium abscessus, Staphylococcus aureus and Pseudomonas aeruginosa. By observing the fat body, gut, trachea, and hemolymph under the microscope, we were able to describe where bacteria tend to disseminate. We also quantified the number of bacteria in the hemolymph throughout the infection course and found significant differences between the different pathogens. With this work, we aimed to better understand the behavior and dissemination of bacteria in the infected larvae.

Scalp Infection Caused by Mycobacterium abscessus Manifested as Patchy Alopecia in an Immunocompetent Female

Mycobacterium abscessus (M. abscessus) is a fast-growing, non-tuberculous mycobacterium (NTM) that can cause human infections varying from superficial infection to pulmonary or even systemic infections. The latter is more commonly appeared in immunocompromised patients. The skin infection caused by M. abscessus often appears after trauma or surgical procedure. It is often manifested by subcutaneous nodules, papules, erythema, tender erythematous or violaceous plaques, cellulitis, abscesses, ulcerations, and draining sinuses. Herein, we present a non-typical cutaneous manifestation of M. abscessus infection in a 46-year-old woman who presented with alopecia on the scalp with no itching or pain. The pathogen was isolated and identified as M. abscessus by morphology and DNA sequencing. To our best knowledge, there was no report that this organism could cause skin lesions mimicking patchy alopecia. After 3 months of antibacterial treatment, the cutaneous lesion disappeared, and new growth of hair occurred in this patient.

Immunogenicity and protection against Mycobacterium avium with a heterologous RNA prime and protein boost vaccine regimen

Prophylactic efficacy of two different delivery platforms for vaccination against Mycobacterium avium (M. avium) were tested in this study; a subunit and an RNA-based vaccine. The vaccine antigen, ID91, includes four mycobacterial antigens: Rv3619, Rv2389, Rv3478, and Rv1886. We have shown that ID91+GLA-SE is effective against a clinical NTM isolate, M. avium 2-151 smt. Here, we extend these results and show that a heterologous prime/boost strategy with a repRNA-ID91 (replicon RNA) followed by protein ID91+GLA-SE boost is superior to the subunit protein vaccine given as a homologous prime/boost regimen. The repRNA-ID91/ID91+GLA-SE heterologous regimen elicited a higher polyfunctional CD4+ TH1 immune response when compared to the homologous protein prime/boost regimen. More significantly, among all the vaccine regimens tested only repRNA-ID91/ID91+GLA-SE induced IFN-γ and TNF-secreting CD8+ T cells. Furthermore, the repRNA-ID91/ID91+GLA-SE vaccine strategy elicited high systemic proinflammatory cytokine responses and induced strong ID91 and an Ag85B-specific humoral antibody response a pre- and post-challenge with M. avium 2-151 smt. Finally, while all prophylactic prime/boost vaccine regimens elicited a degree of protection in beige mice, the heterologous repRNA-ID91/ID91+GLA-SE vaccine regimen provided greater pulmonary protection than the homologous protein prime/boost regimen. These data indicate that a prophylactic heterologous repRNA-ID91/ID91+GLA-SE vaccine regimen augments immunogenicity and confers protection against M. avium.

Updated Review on the Mechanisms of Pathogenicity in Mycobacterium abscessus, a Rapidly Growing Emerging Pathogen

In recent years, Mycobacterium abscessus has appeared as an emerging pathogen, with an increasing number of disease cases reported worldwide that mainly occur among patients with chronic lung diseases or impaired immune systems. The treatment of this pathogen represents a challenge due to the multi-drug-resistant nature of this species and its ability to evade most therapeutic approaches. However, although predisposing host factors for disease are well known, intrinsic pathogenicity mechanisms of this mycobacterium are still not elucidated. Like other mycobacteria, intracellular invasiveness and survival inside different cell lines are pathogenic factors related to the ability of M. abscessus to establish infection. Some of the molecular factors involved in this process are well-known and are present in the mycobacterial cell wall, such as trehalose-dimycolate and glycopeptidolipids. The ability to form biofilms is another pathogenic factor that is essential for the development of chronic disease and for promoting mycobacterial survival against the host immune system or different antibacterial treatments. This capability also seems to be related to glycopeptidolipids and other lipid molecules, and some studies have shown an intrinsic relationship between both pathogenic mechanisms. Antimicrobial resistance is also considered a mechanism of pathogenicity because it allows the mycobacterium to resist antimicrobial therapies and represents an advantage in polymicrobial biofilms. The recent description of hyperpathogenic strains with the potential interhuman transmission makes it necessary to increase our knowledge of pathogenic mechanisms of this species to design better therapeutic approaches to the management of these infections.

Mycobacterium abscessus Complex Osteomyelitis of the Wrist

Mycobacterium abscessus (M. abscessus) is a ubiquitous, rapidly growing non-tuberculous mycobacterium, which is known to cause life-threatening lung infections in immunocompromised individuals following exposure to contaminated injectable products. We report a case of M. abscessus osteomyelitis of the right wrist in a 28-year-old patient with a history of intravenous drug use and a recent surgical repair of the right radial artery pseudoaneurysm. The patient underwent surgical debridement of the right distal radius infection. Histopathological examination and culture of the debrided tissue revealed M. abscessus complex infection. The patient was placed on intravenous amikacin, azithromycin, and cefoxitin for six weeks, followed by oral linezolid and clofazimine for six months.

Omadacycline for management of Mycobacterium abscessus infections: a review of its effectiveness, place in therapy, and considerations for use

The Mycobacterium abscessus complex (MABC) is a group of acid-fast, rapidly dividing non-tuberculous mycobacteria (NTM) that include a number of clinically important subspecies, including M. abscessus, M. bolletii, and M. massiliense. These organisms are prevalent in the environment and are primarily associated with human pulmonary or skin and skin structure infections (SSSI) but may cause more deep-seeded disseminated infections and bacteremia in the immunocompromised. Importantly, these NTM are resistant to most first-line anti-tuberculous agents and, due to intrinsic or acquired resistance, exhibit exceedingly low, variable, and geographically distinct susceptibilities to commonly used antibacterial agents including older tetracyclines, macrolides, aminoglycosides, cephalosporins, carbapenems, and sulfamethoxazole-trimethoprim. Omadacycline is a novel third-generation member of the tetracycline family of antibacterials that has recently been demonstrated to have potent anti-NTM effects and clinical efficacy against MABC, including M. abscessus. The purpose of this review is to present a comprehensive and up-to-date assessment on the body of literature on the role of omadacycline for M. abscessus infections. Specifically, the in vitro and in vivo microbiology, mechanisms of action, mechanisms of resistance, clinical pharmacokinetics, clinical efficacy, adverse effects, dosage and administration, and place in therapy of omadacycline in management of M. abscessus infections will be detailed.

Mycobacterium abscessus Mutants with a Compromised Functional Link between the Type VII ESX-3 System and an Iron Uptake Mechanism Reliant on an Unusual Mycobactin Siderophore

The opportunistic pathogen Mycobacterium abscessus subsp. abscessus (Mab) has become an emerging public health threat due to the increasing number of Mab-associated chronic pulmonary disease cases. Treatment requires multiple drug courses and is often combined with surgical resection. Cure rates are only ~50% due to treatment failure and comorbidities. Deeper understanding of the biology of Mab is required to illuminate potential avenues for the development of better therapeutics against Mab infections. The ESX-3 type VII protein secretion system of Mab has an important role in host inflammatory and pathological responses during infection. In this work, we demonstrate a functional link between ESX-3 and an iron uptake system based on an unusual mycobactin-type siderophore (designated MBT Ab) and exploit this link to implement a large screen for transposon mutants with an impaired ESX-3. Most mutants we identified carry insertions in genes encoding predicted ESX-3 secretion machinery components or potential ESX-3 substrates. The mutants overproduce MBT Ab, a trait consistent with an iron uptake defect. Our characterization of MBT Ab revealed structural features reminiscent of nocardial mycobactin-like compounds with cytotoxicity. This finding raises the possibility that MBT Ab may play roles in pathogenesis unlinked to iron homeostasis. The mutants generated herein will facilitate research to better understand the role of ESX-3 and its interplay with the siderophore system.

Purulent Flexor Tendon Rupture of the Hand due to Mycobacterium abscessus Infection: A Case Report and Review of the Literature

Mycobacterium abscessus infection of the upper extremities is uncommon. However, M abscessus can cause severe chronic tenosynovitis, and delayed diagnosis may result in poor outcomes. We describe an unusual clinical case of purulent flexor tendon synovitis followed by subcutaneous tendon rupture due to M abscessus infection in a patient with diabetes mellitus. A 76-year-old man presented to our hospital with painful, erythematous swelling over his left fourth finger. On physical examination, the left fourth finger was swollen and reddish, with persistent exudate from the surgical scar. The left elbow was also swollen and reddish with persistent discharge, which was consistent with olecranon bursitis. The patient was unable to flex his left fourth finger, and the passive range of motion of the finger was also restricted. The physical examination findings and patient history suggested purulent flexor tendinitis. His infection healed after radical debridement of necrotic tissue and administration of antibiotics effective against M abscessus. Third-stage flexor reconstruction restored the function of the fourth finger. The combination of surgical debridement and chemotherapy was the most effective treatment for mycobacterial tenosynovitis. This case shows that M abscessus can cause chronic severe purulent tenosynovitis and flexor tendon rupture after tendon surgery. Although early diagnosis and combination treatment with debridement and chemotherapy might improve outcomes by limiting the severity and duration of damage to the flexor synovial system, late-presenting patients require combined radical debridement of necrotic tissue and aggressive chemotherapy followed by staged flexor tendon reconstruction.

A Rare Insidious Case of Skin and Soft Tissue Infection Due to Mycobacterium abscessus: A Case Report

Mycobacterium abscessus complex (MABc) is part of the rapid-growing non-tuberculous mycobacteria group that usually resides in natural water sources. When it affects humans, it can be highly resistant and difficult to manage. The most common presentation is localized, mainly in the lungs and soft tissue, but can be generalized in immunocompromised patients. Here we present a case report of a 40-year-old female with a chronic infection of the abdominal wall after abdominoplasty.

Catheter-related infections caused by Mycobacterium abscessus in a patient with motor neurone disease: A case report

BACKGROUND

Mycobacterium abscessus (M. abscessus) is a rapidly growing mycobacterium and ubiquitous in the environment, which infrequently causes disease in humans. However, it can cause cutaneous or respiratory infections among immunocompromised hosts. Due to the resistance to most antibiotics, the pathogen is formidable and difficult-to-treat.

CASE SUMMARY

Here, we present a case of catheter-related M. abscessus infections in a patient with motor neurone disease. Catheter and peripheral blood cultures of the patient showed positive results during Gram staining and acid-fast staining. The alarm time of catheter blood culture was 10.6 h earlier than that of peripheral blood. After removal of the peripherally inserted central catheter, secretion and catheter blood culture were positive. M. abscessus was identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry and 16S rDNA sequencing.

CONCLUSION

For catheter-related M. abscessus infection, rapid diagnosis and timely and adequate antimicrobial therapy are crucial.

Evaluation of antimicrobial susceptibilities of non-tuberculous mycobacteria against linezolid and tigecycline

Mycobacterial susceptibility testing is important for the management of nontuberculous mycobacteria (NTM) infections. The aim of the study is to determine the susceptibilities of tigecycline (TGC) and linezolid (LZD) against NTM. The study was carried out using stocks of NTM strains in the tuberculosis department of the microbiology laboratory. It was designed a retrospective study. LZD and TGC sensitivities of study isolates were analyzed by microdilution. Forty NTM isolates have been studied. LZD and TGC sensitivities varied according to the NTM type. It is concluded that each isolate should be individually evaluated due to variable susceptibilities to LZD and TGC.

Antibiotic susceptibility of mycobacteria isolated from ornamental fish

Introduction

Nontuberculous mycobacteria (NTM) are increasingly recognised as causative agents of opportunistic infections in humans for which effective treatment is challenging. There is very little information on the prevalence of NTM drug resistance in Poland. This study was aimed to evaluate the susceptibility to antibiotics of NTM, originally isolated from diseased ornamental fish.

Material and Methods

A total of 99 isolates were studied, 50 of them rapidly growing mycobacteria (RGM) (among which three-quarters were Mycobacterium chelonae, M. peregrinum, and M. fortuitum and the rest M. neoaurum, M. septicum, M. abscessus, M. mucogenicum, M. salmoniphilum, M saopaulense, and M. senegalense). The other 49 were slowly growing mycobacteria (SGM) isolates (among which only one was M. szulgai and the bulk M. marinum and M. gordonae). Minimum inhibitory concentrations for amikacin (AMK), kanamycin (KAN), tobramycin (TOB), doxycycline (DOX), ciprofloxacin (CIP), clarithromycin (CLR), sulfamethoxazole (SMX), isoniazid (INH) and rifampicin (RMP) were determined.

Results

The majority of the isolates were susceptible to KAN (95.95%: RGM 46.46% and SGM 49.49%), AMK (94.94%: RGM 45.45% and SGM 49.49%), CLR (83.83%: RGM 36.36% and SGM 47.47%), SMX (79.79%: RGM 30.30% and SMG 49.49%), CIP (65.65%: RGM 24.24% and SGM 41.41%), and DOX (55.55%: RGM 9.06% and SGM 46.46%). The majority were resistant to INH (98.98%: RGM 50.50% and SGM 48.48%) and RMP (96.96%: RGM 50.50% and SGM 46.46%).

Conclusion

The drug sensitivity of NTM varies from species to species. KAN, AMK, CLR and SMX were the most active against RGM isolates, and these same four plus DOX and CIP were the best drugs against SGM isolates.

First report of disseminated Mycobacterium abscessus in an immunocompetent adult patient in Oman

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This case report describes the first case of disseminated Mycobacterium abscessus in an immunocompetent adult, and the second reported case of M. abscessus causing native joint septic arthritis.

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Disseminated M. abscessus treatment was given.

Mycobacterium abscessus is a ubiquitous rapid-growing mycobacterium that belongs to a diverse group of non-tuberculous mycobacteria. It can cause frequent and serious infections in patients with or without risk factors. This article reports a case of disseminated M. abscessus in an immunocompetent Omani male with native joint septic arthritis.

Mycobacterium abscessus urinary tract infection in an immunocompetent host: A case report and literature review

Mycobacterium abscessus is one of the nontuberculous mycobacteria (NTM), which can cause many clinical spectra, predominantly pulmonary infections followed by skin and soft tissue infections. The prevalence of Mycobacterium abscessus infections has been growing worldwide over the last two decades. Urinary tract infection (UTI) secondary to M. abscessus is a rare condition, and only five cases have been described in the literature so far. Therefore, managing such a condition is challenging and based on limited evidence. Here, we report a case of an adult male with a history of previous urological procedures who presented with lower urinary tract symptoms (LUTS) and was found to have a UTI secondary to Mycobacterium abscessus. In this case, we described our successful management approach of this rare entity of Mycobacterium abscessus infection, and we reviewed similar cases in the literature.

Mycobacterium abscessus Periprosthetic Hip Infection Complicated by Superimposed Polymicrobial Infection: A Case Report

CASE

A 79-year-old man developed Mycobacterium abscessus prosthetic joint infection (PJI) after hip hemiarthroplasty that was complicated by polymicrobial infection. He was ultimately treated with resection arthroplasty and chronic suppressive therapy. He has had no evidence of recurrent infection after 2 years of follow-up.

CONCLUSION

As far as we know, this is the first reported case of M. abscessus hip PJI complicated by superimposed polymicrobial infection. This case demonstrates the challenge of treating M. abscessus infection, the need for a multidisciplinary approach with aggressive surgical intervention, and prolonged combination antimicrobial therapy for a successful outcome.

Combination treatment with antibiotics and surgical lung resection for Mycobacterium abscessus pulmonary infection in a breast cancer patient

A 51-year-old woman was admitted to our hospital because of pneumonia after chemotherapy with doxorubicin and cyclophosphamide for left breast cancer. The patient was diagnosed with Mycobacterium abscessus pulmonary infection by the detection of M. abscessus complex (MABC) in sputum cultures. However, MABC is intrinsically resistant to most of the antibacterial agents, and MABC pulmonary disease outcomes with modern antibiotic treatment are currently the worst among all mycobacterial species. We herein report the successful treatment of M. abscessus pulmonary infection by a combination treatment with antibiotics and surgical lung resection.

Drug susceptibiity testing of nontuberculous mycobacteria by broth microdilution method

INTRODUCTION

-Incidence of Nontuberculous mycobacteria (NTM) has been increasing in past few years. Treatment of NTM differs from Mycobacterium tuberculosis. For proper treatment, it's important to carry out Drug Susceptibility Testing of NTM. Method of DST for NTM is different from MTB and is not available in most laboratories.

METHOD

-We performed DST on 122 isolates of NTM. Amikacin, Ciprofloxacin, Trimethoprim, Doxycycline, Moxifloxacin, Clarithromycin, Minocycline and Cefoxitin were used for Rapid Growing Mycobacteria (RGM) and Rifampicin, Clarithromycin, Ethambutol, Isoniazid and Moxifloxacin for Slow Growing Mycobacteria (SGM). M. avium Complex (MAC) was tested against Clarithromycin. Minimum inhibitor concentration was calculated as recommended by standard Clinical and Laboratory Standards Institute (CLSI) and Resazurin Microtitre Assay (REMA).

RESULT

-Most of Rapid Growing Mycobacteria were sensitive to Amikacin (76.1%) and Moxifloxacin (46.47%) while Slow Growing Mycobacteria showed only 33.3% sensitivity to Rifampicin and Moxifloxacin and 42% to Clarithromycin. M. avium-intracellulare complex showed 45-50% sensitivity to Clarithromycin. Overall, 98% concordance (Kappa = 0.98; almost perfect; 95% CI = 0.966 to 0.996) was seen between standard and REMA method of DST of NTM.

CONCLUSION

-Rapid growers showed good sensitivity to Amikacin and Moxifloxacin, while only one third SGM showed sensitivity to Rifampicin, Moxifloxacin and Clarithromycin. For proper management of NTM of eastern Rajasthan its important to know the DST profile in our area to initiate empirical therapy till the results of specific patient are available. REMA was found to give excellent concordance with standard method.

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.

Clinical and demographic study of non-tuberculous mycobacterial ocular infections in South India

PURPOSE

To describe demographics, risk factors, antibiotic susceptibility, management and outcomes of ocular infections caused by non-tuberculous mycobacteria (NTM).

METHODS

A retrospective review of medical case records and microbiology records of patients with ocular infections that were culture positive for non-tuberculous Mycobacteria from January 2014 to December 2018 was done. Antibiotic susceptibility profile was done based on the CLSI guidelines. Laboratory diagnosis for the NTM Species was done by conventional microbiological methods. The species identification was done for stored isolated utilizing polymerase chain reaction targeting 16S rDNA and rpoB gene, followed by DNA sequencing and phylogenetic analysis.

RESULTS

Twenty patients with NTM ocular infections were identified during the study period. A majority of cases presented as 12 infectious keratitis (60%) and three suture-related corneal infiltrates (15%). Common risk factors were history of trauma in 9 (45%) patients and history of ocular surgery in 5 (25%) patients. Patients were treated with combination of amikacin and flouroquinolones/chloramphenicol (70%) and surgical interventions were performed in 25% cases. Only twelve isolates were stored and ten isolates were identified as the M. abscessus subsp. abscessus and two isolates as M. abscessus subsp. massiliense by sequencing and phylogenetic analysis. Majority of the NTM were sensitive to amikacin (75%) followed by moxifloxacin, ciprofloxacin, cephotaxime and tobramycin (35%).

CONCLUSION

High degree of clinical suspicion, multidrug antibiotic therapy and timely surgical intervention in patients with NTM infections, are advised for better clinical outcomes. Prior ocular trauma, prior ocular surgery and presence of biomaterials were the major predisposing factors. Earlier surgical intervention in cases where abscesses or biomaterials are involved, is necessary for rapid recovery.

General Overview of Nontuberculous Mycobacteria Opportunistic Pathogens: Mycobacterium avium and Mycobacterium abscessus

Nontuberculous mycobacteria (NTM) are emerging human pathogens, causing a wide range of clinical diseases affecting individuals who are immunocompromised and who have underlying health conditions. NTM are ubiquitous in the environment, with certain species causing opportunistic infection in humans, including Mycobacterium avium and Mycobacterium abscessus. The incidence and prevalence of NTM infections are rising globally, especially in developed countries with declining incidence rates of M. tuberculosis infection. Mycobacterium avium, a slow-growing mycobacterium, is associated with Mycobacterium avium complex (MAC) infections that can cause chronic pulmonary disease, disseminated disease, as well as lymphadenitis. M. abscessus infections are considered one of the most antibiotic-resistant mycobacteria and are associated with pulmonary disease, especially cystic fibrosis, as well as contaminated traumatic skin wounds, postsurgical soft tissue infections, and healthcare-associated infections (HAI). Clinical manifestations of diseases depend on the interaction of the host's immune response and the specific mycobacterial species. This review will give a general overview of the general characteristics, vulnerable populations most at risk, pathogenesis, treatment, and prevention for infections caused by Mycobacterium avium, in the context of MAC, and M. abscessus.

Mycobacterium abscessus exit-site infection in peritoneal dialysis patients: should we ever aim to salvage the catheter?

Improvements in the exit-site care for peritoneal dialysis (PD) patients have uncovered a trend for increasing incidence of rapidly growing nontuberculous mycobacterium exit-site infections (ESI). Among these, Mycobacterium abscessus is unique in terms of its high morbidity and treatment failure rates. The international society of PD guidelines encourage PD catheter removal in patients with M. abscessus peritonitis but, do not have evidence-based recommendations for the management of ESIs related to this organism. We report an unusual case in which an asymptomatic end-stage renal disease patient with multiple favorable clinical characteristics, i.e., no apparent immunodeficiency, sensitivity pattern showing possibility of treatment with multiple antibiotics, no evidence of peritonitis, and early clinical response, was treated with a 9-month combination antimicrobial regimen administered orally and intraperitoneally. Despite excellent clinical response with a resolution of the ESI, our patient relapsed quickly, within 30 days of stopping antimicrobial therapy and required PD catheter removal. Our case, taken together with available published case reports, highlights the futility of the conservative approach towards the M. abscessus ESI and makes the cases for early PD catheter removal in these patients.

Exposure of Mycobacterium abscessus to Environmental Stress and Clinically Used Antibiotics Reveals Common Proteome Response among Pathogenic Mycobacteria

Mycobacterium abscessus subsp. abscessus (MAB) is a clinically important nontuberculous mycobacterium (NTM) causing pulmonary infection in patients such as cystic fibrosis and bronchiectasis. MAB is naturally resistant to the majority of available antibiotics. In attempts to identify the fundamental response of MAB to aerobic, anaerobic, and biofilm conditions (as it is encountered in patients) and during exposure to antibiotics, we studied bacterial proteome using tandem mass tag mass spectrometry sequencing. Numerous de novo synthesized proteins belonging to diverse metabolic pathways were found in anaerobic and biofilm conditions, including glycolysis/gluconeogenesis, tricarboxylic acid (TCA) cycle, oxidative phosphorylation, nitrogen metabolism, and glyoxylate and dicarboxylate metabolism. Upon exposure to amikacin and linezolid under stress environments, MAB displayed metabolic enrichment for glycerophospholipid metabolism and oxidative phosphorylation. By comparing proteomes of two significant NTMs, MAB and M. avium subsp. hominissuis, we found highly synthesized shared enzymes of oxidative phosphorylation, TCA cycle, glycolysis/gluconeogenesis, glyoxylate/dicarboxylate, nitrogen metabolism, peptidoglycan biosynthesis, and glycerophospholipid/glycerolipid metabolism. The activation of peptidoglycan and fatty acid biosynthesis pathways indicates the attempt of bacteria to modify the cell wall, influencing the susceptibility to antibiotics. This study establishes global changes in the synthesis of enzymes promoting the metabolic shift and enhancing the pathogen resistance to antibiotics within different environments.

Mycobacterium abscessus mimicking tubercular spondylodiscitis following ozone therapy: A case report and review of literature

Background:

The incidence of Mycobacterium abscessus (MA), a rapidly growing species of nontuberculous mycobacteria (NTM)-related infections, has been steadily rising over the past decade. Despite the increased prevalence of NTM-related infections, it is largely underreported from TB-endemic countries due to lack of awareness and limited laboratory facilities. Here, we report a rare case of L4–L5 spondylodiscitis caused by MA following ozone therapy (a noncondoned method of lumbar disc management).

Case Description:

A healthy, nonimmunocompromised 43-year-old female presented with bilateral lower extremity radiculopathy. She underwent a fluoroscopically guided percutaneous ozone treatment for degenerated disc disease at the L4–L5 level. She was symptom free for 3 months duration. She then presented with severe low back pain, bilateral lower extremity radiculopathy, and spondylodiscitis at the L4–L5 level. This was treated with a L4–L5 transforaminal lumbar interbody fusion. MA was cultured from the epidural purulent material collected during the surgery. The patient was discharged on oral clarithromycin 500 mg twice daily and intravenous amikacin 500 mg twice daily for 6 weeks. The plan was to then continue oral clarithromycin for another 6 weeks till resolution of primary infection.

Conclusion:

Early diagnosis and appropriate therapy is required to treat NTM which is more prevalent in epidemic/endemic regions.

T9-T10 Osteomyelitis, Epidural Abscess and Cord Compression Secondary to Mycobacterium abscessus: A Case Report

BACKGROUND

We report a case of spinal abscess/osteomyelitis at the T9-T10 levels in a non-immunocompromised patient who presented with lower extremity weakness secondary to a Mycobacterium abscessus infection. This patient was successfully treated with surgical debridement with amikacin-tigecycline-imipenem triple therapy before and after her debridement. Outcomes and treatment with this rare cause of epidural abscess/osteomyelitis are not well defined at this time.

CASE REPORT

Clinical Presentations with this species of mycobacterium are usually systemic with patients presenting with pulmonary and soft tissue infections. The primary presentation of spinal epidural abscess/osteomyelitis is unusual, especially when there is no primary focus such as a lung infection or concurrent bacteremia.

CONCLUSION

This paper presents a new case of spinal osteomyelitis without a primary source in addition to 10 previously reported M. abscessus cases. The treatment plans and outcomes suggest that surgical debridement along with a macrolide-based combination therapy should be considered a definitive treatment against Mycobacterium abscesses.

Non-pigmented rapidly growing mycobacteria smooth and rough colony phenotypes pathogenicity evaluated using in vitro and experimental models

Non-pigmented rapidly growing mycobacteria (NPRGM) are widely distributed in water, soil and animals. It has been observed an increasing importance of NPRGM related-infections, particularly due to the high antimicrobial resistance. NPRGM have rough and smooth colony phenotypes, and several studies have showed that rough colony variants are more virulent than smooth ones. However, other studies have failed to validate this observation. In this study, we have performed two models, invitro and in vivo, in order to assess the different pathogenicity of these two phenotypes. We used collection and clinical strains of Mycobacteriumabscessus, Mycobacterium fortuitum and Mycobacteriumchelonae. On the invitro model (macrophages), phagocytosis was higher for M. abscessus and M. fortuitum rough colony variant strains when compared to smooth colony variants. However, we did not find differences with colonial variants of M. chelonae. Survival of Galleriamellonella larvae in the experimental model was lower for M. abscessus and M. fortuitum rough colony variants when compared with larvae infected with smooth colony variants. We did not find differences in larvae infected with M. chelonae.Results of our in vivo study correlated well with the experimental model. This fact could have implications on the interpretation of the clinical significance of the NPRGM isolate colonial variants.

Mycobacterium abscessus mimicking tubercular spondylodiscitis following ozone therapy: A case report and review of literature

Background:

The incidence of Mycobacterium abscessus (MA), a rapidly growing species of nontuberculous mycobacteria (NTM)-related infections, has been steadily rising over the past decade. Despite the increased prevalence of NTM-related infections, it is largely underreported from TB-endemic countries due to lack of awareness and limited laboratory facilities. Here, we report a rare case of L4–L5 spondylodiscitis caused by MA following ozone therapy (a noncondoned method of lumbar disc management).

Case Description:

A healthy, nonimmunocompromised 43-year-old female presented with bilateral lower extremity radiculopathy. She underwent a fluoroscopically guided percutaneous ozone treatment for degenerated disc disease at the L4–L5 level. She was symptom free for 3 months duration. She then presented with severe low back pain, bilateral lower extremity radiculopathy, and spondylodiscitis at the L4–L5 level. This was treated with a L4–L5 transforaminal lumbar interbody fusion. MA was cultured from the epidural purulent material collected during the surgery. The patient was discharged on oral clarithromycin 500 mg twice daily and intravenous amikacin 500 mg twice daily for 6 weeks. The plan was to then continue oral clarithromycin for another 6 weeks till resolution of primary infection.

Conclusion:

Early diagnosis and appropriate therapy is required to treat NTM which is more prevalent in epidemic/endemic regions.

Mycobacterium abscessus infection leads to enhanced production of type 1 interferon and NLRP3 inflammasome activation in murine macrophages via mitochondrial oxidative stress

Mycobacterium abscessus (MAB) is a rapidly growing mycobacterium (RGM), and infections with this pathogen have been increasing worldwide. Recently, we reported that rough type (MAB-R) but not smooth type (MAB-S) strains enhanced type 1 interferon (IFN-I) secretion via bacterial phagosome escape, contributing to increased virulence. Here, we sought to investigate the role of mitochondrial oxidative stress in bacterial survival, IFN-I secretion and NLRP3 inflammasome activation in MAB-infected murine macrophages. We found that live but not heat-killed (HK) MAB-R strains increased mitochondrial ROS (mtROS) and increased release of oxidized mitochondrial DNA (mtDNA) into the cytosol of murine macrophages compared to the effects of live MAB-S strains, resulting in enhanced NLRP3 inflammasome-mediated IL-1β and cGAS-STING-dependent IFN-I production. Treatment of the infected macrophages with mtROS-modulating agents such as mito-TEMPO or cyclosporin A reduced cytosolic oxidized mtDNA, which inhibited the MAB-R strain-induced production of IL-1β and IFN-I. The reduced cytosolic oxidized mtDNA also inhibited intracellular growth of MAB-R strains via cytosolic escape following phagosomal rupture and via IFN-I-mediated cell-to-cell spreading. Moreover, our data showed that mtROS-dependent IFN-I production inhibited IL-1β production, further contributing to MAB-R intracellular survival in murine macrophages. In conclusion, our data indicated that MAB-R strains enhanced IFN-I and IL-1β production by inducing mtROS as a pathogen-associated molecular pattern (PAMP). These events also enhance bacterial survival in macrophages and dampen inflammation, which contribute to the pathogenesis of MAB-R strains.

MAB infections have gained increasing attention due to their clinical significance. Mitochondrial oxidative stress regulates intrinsic innate immune responses mainly via IFN-I or IL-1β production, which affects the pathogenesis of several pathogens, including Mycobacterium tuberculosis infections. Here, we found that virulent MAB-R but not MAB-S strains induced mtROS in infected macrophages, resulting in enhanced IFN-I and IL-1β production by the release of oxidized mtDNA into the cytosol. Furthermore, increased mtROS exerted a pro-bacterial effect by inducing IFN-I-mediated escape of MAB-R into the cytosol. In MAB-R-infected murine macrophages, mtROS-induced IFN-I also inhibited IL-1β production exerting an antibacterial effect, further contributing to intracellular bacterial survival. Our data indicate that mtROS play an important role in MAB-R pathogenesis by facilitating bacterial survival and dampening inflammation in macrophages as a kind of specific class of PAMP. mtROS may be a valuable target for the treatment of virulent MAB infections.

Outcome according to subspecies following lung transplantation in cystic fibrosis pediatric patients infected with Mycobacterium abscessus

BACKGROUND

Mycobacterium abscessus infection has been associated with variable outcomes following lung transplantation. M abscessus comprises three subspecies (M abscessus subsp abscessus, M abscessus subsp massiliense, and M abscessus subsp bolletii). We investigated whether lung transplantation outcome in cystic fibrosis (CF) patients in a single center was related to the M abscessus subspecies and genetic cluster.

METHODS

CF patients with chronic M abscessus infection transplanted at Great Ormond Street Hospital between 2004 and 2017 were retrospectively examined. All M abscessus isolates were identified to subspecies level by polymerase chain reaction and sequencing. Genetic cluster was determined by variable number tandem repeat profiling and whole-genome sequencing (WGS), and sequence type inferred from WGS.

RESULTS

Thirteen patients with chronic M abscessus infection underwent heart/lung or lung transplantation. Subspecies identification showed n = 1 with M abscessus bolletii, n = 5 with M abscessus massiliense, and n = 7 with M abscessus abscessus infection. Eight (62%) patients (one with M abscessus massiliense and seven with M abscessus abscessus) died post-lung transplant. The patient with M abscessus bolletii and three patients with M abscessus massiliense did well post-transplant. One patient with M abscessus massiliense is receiving ongoing treatment.

CONCLUSIONS

Dramatically worse outcomes are observed in patients infected with M abscessus subspecies abscessus, the majority of whom were infected with ST-1 and ST-26 strains. Patients infected with other M abcsessus strains can have acceptable outcomes.

Effect of Amoxicillin in combination with Imipenem-Relebactam against Mycobacterium abscessus

Infections caused by Mycobacterium abscessus are increasing in prevalence in cystic fibrosis patients. This opportunistic pathogen's intrinsic resistance to most antibiotics has perpetuated an urgent demand for new, more effective therapeutic interventions. Here we report a prospective advance in the treatment of M. abscessus infection; increasing the susceptibility of the organism to amoxicillin, by repurposing the β-lactamase inhibitor, relebactam, in combination with the front line M. abscessus drug imipenem. We establish by multiple in vitro methods that this combination works synergistically to inhibit M. abscessus. We also show the direct competitive inhibition of the M. abscessus β-lactamase, Bla_Mab, using a novel assay, which is validated kinetically using the nitrocefin reporter assay and in silico binding studies. Furthermore, we reverse the susceptibility by overexpressing Bla_Mab in M. abscessus, demonstrating relebactam-Bla_Mab target engagement. Finally, we highlight the in vitro efficacy of this combination against a panel of M. abscessus clinical isolates, revealing the therapeutic potential of the amoxicillin-imipenem-relebactam combination.

THP-1 and Dictyostelium Infection Models for Screening and Characterization of Anti-Mycobacterium abscessus Hit Compounds

!!NCR1!! presents a great challenge to antimycobacterial therapy due to its innate resistance against most antibiotics. M. abscessus is able to grow intracellularly in human macrophages, suggesting that intracellular models can facilitate drug discovery. Thus, we have developed two host cell models: human macrophages for use in a new high-content screening method for M. abscessus growth and a Dictyostelium discoideum infection model with the potential to simplify downstream genetic analysis of host cell factors. A screen of 568 antibiotics for activity against intracellular M. abscessus led to the identification of two hit compounds with distinct growth inhibition. A collection of 317 human kinase inhibitors was analyzed, with the results yielding three compounds with an inhibitory effect on mycobacterial growth, strengthening the notion that host-directed therapy can be applied for M. abscessus.

Medical management of atraumatic Mycobacterium abscessus cutaneous infection: A case report

Treatment for cutaneous infection from Mycobacterium abscessus is fraught with poorly established evidence. Given its antibiotic multi-resistance, surgical intervention is often recommended. We report a case of cutaneous M. abscessus infection that was successfully managed with medical therapy alone. A 55-year-old immunocompetent woman from the Bellarine peninsula in Victoria, Australia presented to our hospital with a 2-week history of a non-healing ulcer on her left forearm. The patient had no history of trauma or procedures to the skin. On presentation, the patient had a punch biopsy, which was culture positive for M. abscessus. The isolate was susceptible to clarithromycin and amikacin, had intermediate susceptibility to ciprofloxacin, cefoxitin and linezolid and was resistant to doxycycline, imipenem, cotrimoxazole and moxifloxacin. The tigecycline MIC was 0.25 μg/ml. The patient received a total of 12 weeks of oral clarithromycin 500 mg twice daily, 4 weeks of intravenous amikacin 500 mg daily, 6 weeks of intravenous tigecycline 100 mg over 24 hours via Baxter pump, and 4 weeks of oral clofazimine 100 mg daily. The patient made a good clinical recovery and had her medical therapy ceased after 12 weeks. M. abscessus cutaneous infection in an immunocompetent individual without antecedent trauma or surgery is rare. Our case illustrates the successful treatment of a deep M. abscessus cutaneous ulcer with relatively short duration macrolide-based antibiotic therapy without any surgical intervention.

Successful management of severe post-LASIK Mycobacterium abscessus keratitis with topical amikacin and linezolid, flap ablation, and topical corticosteroids

This is a case report of post-laser in situ keratomileusis (LASIK) multidrug-resistant Mycobacterium abscessus keratitis managed with combined topical amikacin and linezolid, flap amputation, and corticosteroids. A 34-year-old woman presented with a corneal interface infiltrate 3 weeks after LASIK. Cultures isolated mycobacteria. The infiltrate did not improve under intensive topical therapy and interface irrigation with empiric antibiotics over 5 weeks, and the infiltrate progressed to severe inflammation and stromal neovascularization. After identification of M abscessus susceptible only to amikacin and linezolid, antimicrobials were adjusted and the flap was ablated. Cultures repeated 1 week later came back negative. However, stromal inflammation and neovascularization persisted. Topical steroids achieved regression of the inflammation within 1 week. Identification of the mycobacterial pathogen and its susceptibilities is essential given the possibility of multidrug resistance. Topical linezolid can be effective in susceptible species. Corticosteroids can be helpful in cases with severe inflammation.

Mycobacteriumabscessus-associated vertebral osteomyelitis in an immunocompetent patient: a rare case report and literature review

Introduction

Vertebral osteomyelitis (VO) is an uncommon infection with Staphylococcus aureus as the most commonly implicated organism. VO caused by nontuberculous mycobacteria (NTM) such as Mycobacteriumabscessus (M. abscesscus) is exceedingly rare with only eight cases reported in literature.

Case presentation

We report a rare case of an 82-year-old male with a remote history of trauma who was diagnosed with NTM vertebral osteomyelitis. The patient initially underwent a vertebroplasty of T12 and kyphoplasty of L1 for pathologic compression fractures. Subsequent cultures revealed M. abscessus. The patient further underwent an anterior T12-L2 corpectomy and debridement with instrumented fusion, as well as a posterior T9-L4 instrumentation and fusion. He received multi-agent antibiotic therapy; however, was ultimately unable to tolerate the aggressive treatment regimen and his prolonged postoperative course.

Discussion

Nontuberculous mycobacteria vertebral osteomyelitis is exceedingly rare. NTM vertebral osteomyelitis is challenging to treat. Surgical management plays a limited role in early VO, but is the mainstay treatment in chronic VO. Early recognition of the condition and shared patient management with multidisciplinary teams is key to successfully treating cases of NTM VO.

In Vitro Activity of New Tetracycline Analogs Omadacycline and Eravacycline against Drug-Resistant Clinical Isolates of Mycobacterium abscessus

Tigecycline is used in multidrug regimens for salvage therapy of Mycobacterium abscessus infections but is often poorly tolerated and has no oral formulation. Here, we report similar in vitro activity of two newly approved tetracycline analogs, omadacycline and eravacycline, against 28 drug-resistant clinical isolates of M. abscessus complex. Since omadacycline and eravacycline appear to be better tolerated than tigecycline and since omadacycline is also formulated for oral dosing, these tetracycline analogs may represent new treatment options for M. abscessus infections.

Genetic correlates of clarithromycin susceptibility among isolates of the Mycobacterium abscessus group and the potential clinical applicability of a PCR-based analysis of erm(41)

Objectives

To define the genetic basis of clarithromycin resistance among isolates of the Mycobacterium abscessus group (MAG).

Methods

We analysed 133 isolates identified as MAG. Species identification was confirmed by sequencing the rpoB gene. Clarithromycin susceptibility testing was performed according to CLSI recommendations, with an extended 14 day incubation. Known resistance genotypes of erm(41) and rrl were identified by sequencing; the presence of deletions in erm(41) was detected by PCR.

Results

The 133 MAG isolates included 82 M. abscessus, 27 Mycobacterium massiliense and 24 Mycobacterium bolletii. After the 3 day incubation, only five isolates demonstrated clarithromycin resistance (R); after 14 days of extended incubation, an additional 92 exhibited inducible resistance (IR), with the remaining being susceptible (S). The distribution of susceptibility phenotypes varied among the species. Among M. abscessus isolates, 11% were S, 84% IR and 5% R; among M. bolletii isolates, 96% were IR and 4% R; and among M. massiliense isolates 100% were S. Sequencing of rrl identified only a single isolate with the A2058G mutation. Deletions in erm(41) were present in 30 susceptible isolates; among the remaining 103 isolates, 97 were R or IR (sensitivity, 83%; specificity, 100%; positive predictive value, 100%; negative predictive value, 94%). Among the six susceptible isolates without deletions, all carried the erm(41) T28C point mutation.

Conclusions

A significant proportion of MAG isolates demonstrate inducible resistance to clarithromycin that is only detectable with an extended 14 day incubation. Further, the majority of clarithromycin-susceptible MAG isolates have characteristic deletions in erm(41) that can rapidly and reliably be detected by a simple PCR.

Pulmonary Mycobacterium abscessus complex in children with cystic fibrosis: A practical management guideline

The treatment of Mycobacterium abscessus complex (MABSC) pulmonary infections is an emerging challenge in patients with cystic fibrosis (CF). Multidrug therapy for prolonged durations is required and carries the significant burden of drug-related toxicity, cost and selective pressure for multiresistant bacteria. International guidelines acknowledge that clinical and in vitro data to support treatment regimens are limited, particularly in children. As part of a collaboration between the infectious diseases and respiratory units at our institution, we have developed a modified treatment guideline that aims to balance the aims of MABSC eradication and slowing disease progression with minimising drug toxicity and resistance. The outcomes of this treatment approach will be monitored and reported. In this manuscript, we discuss the available evidence for treatment choices and present our treatment guideline for paediatric patients with CF and MABSC infection.

Dual β-Lactam Combinations Highly Active against Mycobacterium abscessus Complex In Vitro

As a consequence of a growing population of immunocompromised individuals, including transplant recipients and cystic fibrosis patients, there has been a dramatic increase in chronic infections caused by Mycobacterium abscessus complex (MABC) strains that are usually recalcitrant to effective antibiotic therapy. The recent rise of macrolide resistance in MABC has further complicated this clinical dilemma, dramatizing the need for novel agents. The repurposing of current antibiotics is one rapid path from discovery to patient care. In this study, we have discovered that dual β-lactams, and specifically the combination of ceftazidime with either ceftaroline or imipenem, are synergistic and have clinically relevant activities, with MIC50s of 0.25 (ceftaroline with 100 µg/ml ceftazidime) and 0.5 µg/ml (imipenem with 100 µg/ml ceftazidime) against clinical MABC isolates. Similar synergy was observed in time-kill studies against the M. abscessus ATCC 19977 strain using clinically achievable concentrations of either imipenem (4 µg/ml) or ceftaroline (2 µg/ml), as the addition of ceftazidime at concentrations of ≥50 µg/ml showed a persistent bactericidal effect over 5 days. Treatment of THP-1 human macrophages infected with three different M. abscessus clinical isolates supported the in vitro findings, as the combination of 100 µg/ml ceftazidime and 0.125 µg/ml ceftaroline or 100 µg/ml ceftazidime and 0.25 µg/ml imipenem dramatically reduced the CFU counts to near baseline levels of infection. This study's finding that there is synergy between certain β-lactam combinations against M. abscessus infection provides optimism toward identifying an optimum dual β-lactam treatment regimen.IMPORTANCE The emergence of chronic MABC infections among immunocompromised populations and their inherent and acquired resistance to effective antibiotic therapy have created clinical challenges in advancing patients for transplant surgery and treating those with disease. There is an urgent need for new treatment regimens, and the repurposing of existing antibiotics provides a rapid strategy to advance a laboratory finding to patient care. Our recent discoveries that dual β-lactams, specifically the combination of ceftazidime with ceftaroline or ceftazidime with imipenem, have significant in vitro MIC values and kill curve activities and are effective against infected THP-1 human macrophages provide optimism for a dual β-lactam treatment strategy against MABC infections. The unexpected synergistic activities reported in this study create a new path of discovery to repurpose the large family of β-lactam drugs.

Analysis of drug-susceptibility patterns and gene sequences associated with clarithromycin and amikacin resistance in serial Mycobacterium abscessus isolates from clinical specimens from Northeast Thailand

Mycobacterium abscessus is an important infectious agent highly associated with drug resistance and treatment failure. We investigated the drug resistance situation of M. abscessus in Northeast Thailand and the possible genetic basis for this. Sixty-eight M. abscessus clinical isolates were obtained from 26 patients at Srinagarind Hospital during 2012–2016. Drug susceptibility tests and sequencing of erm(41), rrl and rrs genes were performed. Mycobacterium abscessus was resistant to 11/15 antibiotics (nearly 100% resistance in each case). Partial susceptibility to four antibiotics was found (amikacin, tigecycline, clarithromycin and linezolid). Non-massiliense subspecies were significantly associated with clarithromycin resistance (p<0.0001) whereas massiliense subspecies were associated with tigecycline resistance (p = 0.028). Inducible clarithromycin resistance was seen in 22/68 (32.35%) isolates: 21 of these isolates (95.45%) belonged to non-massiliense subspecies and resistance was explicable by the T28C mutation in erm(41). Inducible clarithromycin resistance was found in one isolate of the massiliense subspecies. Acquired clarithromycin resistance explicable by the A2271G/C mutation of rrl was seen in only 7/16 (43.75%) of strains. Inducible and acquired resistance mechanisms can be interchangeable during the course of infection. Rrs mutations were not associated with amikacin resistance in our study. Antibiotic resistance in subspecies of M. abscessus was reported from Northeast Thailand. Known resistance-associated mutations cannot explain all of the resistance patterns observed.

A description of Mycobacterium chelonae subsp. gwanakae subsp. nov., a rapidly growing mycobacterium with a smooth colony phenotype due to glycopeptidolipids

Three rapidly growing mycobacterial strains, MOTTH4W, MOTT36W^T and MOTT68W, were isolated from the sputa of three independent Korean patients co-infected with Mycobacterium yongonense Type II strains. The 16S rRNA gene sequences of all three strains were unique, which were closest to that of Mycobacterium chelonae subsp. bovis KCTC 39630^T (99.9 % similarity). Multilocus sequence typing analysis targeting 10 housekeeping genes including hsp65 and rpoB revealed the distinct phylogenetic location of these strains, which were clustered with M. chelonae subsp. chelonae ATCC 35752^T and M. chelonae subsp. bovis KCTC 39630^T. Phylogenetic analysis based on whole genome sequences revealed a 95.89 % average nucleotide identity (ANI) value with M. chelonae subsp. chelonae, slightly higher than the 95.0 % ANI criterion for determining a novel species. In addition, phenotypic characteristics such as a smooth colony morphology and growth inhibition at 37 °C, distinct MALDI-TOF MS profiles of extracted total lipids due to surface glycopeptidolipids, and distinct drug susceptibility profiles further supported the taxonomic characterization of these strains as representing a novel subspecies of Mycobacterium chelonae. Mycobacterium chelonae subsp. gwanakae subsp. nov. is proposed and the type strain is MOTT36W^T (=KCTC 29127^T=JCM 32454^T).