Abscessus Isolates Research Articles

P-784. Early Prediction of Inducible Macrolide Resistance For Mycobacterium abscessus –Minimum Inhibitory Concentrations at Day 7 Versus Day 14

Abstract Background Mycobacterium abscessus is notoriously difficult to treat. Current guidelines suggest a 14-day long incubation period and/or sequencing of erm41 to detect inducible macrolide resistance when treating pulmonary disease. However, the lengthy incubation is inconvenient, and genotyping is not routinely available nor correlated with treatment outcomes in extrapulmonary infections. We aimed to assess whether a more than two-fold change in minimum inhibitory concentrations (MICs) at D7 can reliably predict inducible macrolide resistance at D14.Table 1.MICs of the included M. abscessus isolates against selected antibiotics and breakpoints interpretationThe only M abscessus sub bolletei had macrolide MIC of 2 (S), 32 (R), 32 (R) on D3, 7, 14, and amikacin MIC of 8 (S), cefoxitin 32 (S), ciprofloxacin 8 (R), doxycycline 32 (R), imipenem 8 (I), linezolid 8 (S), moxifloxacin 8 (R), TMP/SFX > 8/152 (R), tobramycin 16 (I), amoxicillin/clavulanic acid >64/32 (R), ceftriaxone 128 (R), cefepime 64 (R), tigecycline 0.5 (S) Methods Between 2013-2015, 35 M. abscessus isolates were identified from non-pulmonary sites at a medical center in Taiwan. The species were identified using mass spectrometry and sequencing of erm41, and rrl were done. Testing for MIC was done with broth microdilution, with results read on D3, D7, and D14 for macrolides, and all other antibiotics on D3. The isolate is predicted to have inducible macrolide resistance if there is a twofold or more increase in MIC between D3 and D7. The clinical information was obtained from chart review.Table 2.Application of macrolide prediction rule and the correlation with phenotypic and genotypic resistance (N=35) Results There were a total of 35 unique M. abscessus isolates comprising 16 subsp. abscessus, 18 subsp. massiliense and 1 subsp. bolletii. The overall inducible macrolide resistance was 45.7% and 2 of the 5 sequevar C28 M abscessus exhibited inducible macrolides resistance. Using proposed prediction rule, the sensitivity and specificity was 87.5% and 73.7%, respectively; resulting in 2 very major errors (failure to identify inducible macrolide resistance), and comparatively superior to genotypic prediction, resulting in 4 very major errors. From chart review, 80% of the patients received combinatorial treatment, and macrolides were the most widely used antibiotics. 67.9% of them received surgery, or debridement. The overall clinical cure rate was 75%, after a median treatment duration of 6 months.Table 3.Patient characteristicsa: One subject with ESKD under peritoneal dialysis had isolated culture within ascites, one man had MAB growth in pleural effusion.b: One subject had MAB growth in liver abscess, and the other had positive culture in gastric juice.c: 14 (50%) patients got moxifloxacin, 13 (46.4%) patients got levofloxacin and 5 (17.9%) got ciprofloxacin. Conclusion The study highlighted that susceptibility testing read within one week can give meaningful information on inducible macrolide resistance that was not inferior to genotypic information. Further validation of early MIC changes to guide treatment selection is warranted. Disclosures All Authors: No reported disclosures

TBAJ-587, a novel diarylquinoline, is active against Mycobacterium abscessus.

Nontuberculous mycobacteria (NTM) infections are extremely difficult to treat due to a natural resistance to many antimicrobials. TBAJ-587 is a novel diarylquinoline, which shows higher anti-tuberculosis activity, lower lipophilicity, and weaker inhibition of hERG channels than bedaquiline (BDQ). The susceptibilities of 11 NTM reference strains and 194 clinical Mycobacterium abscessus isolates to TBAJ-587 were determined by the broth microdilution assay. The activity of TBAJ-587 toward the growth of M. abscessus in macrophages was also evaluated. Minimum bactericidal concentration and time-kill kinetic assays were conducted to distinguish between the bactericidal and bacteriostatic activities of TBAJ-587. The synergy between TBAJ-587 and eight clinically important antibiotics was determined using a checkerboard assay. TBAJ-587 was highly effective against M. abscessus by targeting its F-ATP synthase c chain. The antimicrobial activities of TBAJ-587 and BDQ toward intracellular M. abscessus were comparable. The in vivo activities of TBAJ-587 and BDQ in an immunocompromised mouse model were also comparable. TBAJ-587 expressed bactericidal activity and was compatible with eight anti-NTM drugs commonly used in clinical practice; no antagonism was discovered. As such, TBAJ-587 represents a potential candidate for the treatment of NTM infections.

Genomic Epidemiology of Extrapulmonary Nontuberculous Mycobacteria Isolates at Emerging Infections Program Sites - United States, 2019-2020.

Nontuberculous mycobacteria (NTM) cause pulmonary and extrapulmonary infections. Although isolation of NTM from clinical specimens has increased nationally, few studies delineated the molecular characteristics of extrapulmonary NTM. Extrapulmonary isolates were collected by four Emerging Infections Program sites from October 2019 to March 2020 and underwent laboratory characterization, including matrix-assisted laser desorption ionization-time of flight mass spectrometry, Sanger DNA sequencing, and whole genome sequencing. Bioinformatics analyses were employed to identify species, sequence types (STs), antimicrobial resistance (AR), and virulence genes; isolates were further characterized by phylogenetic analyses. Among 45 isolates, the predominant species were Mycobacterium avium (n=20, 44%), Mycobacterium chelonae (n=7, 16%), and Mycobacterium fortuitum (n=6, 13%). The collection represented 31 STs across 10 species; the most common ST was ST11 (M. avium, n=7). Mycobacterium fortuitum and Mycobacterium abscessus isolates harbored multiple genes conferring resistance to aminoglycosides, beta-lactams, and macrolides. No known AR mutations were detected in rpoB, 16S, or 23S rRNAs. Slow-growing NTM species harbored multiple virulence genes including type-VII secretion components, adhesion factors, and phospholipase C. Continued active laboratory- and population-based surveillance will further inform the prevalence of NTM species and STs, monitor emerging clones, and allow AR characterization.

Mycobacterium abscessus strain variability in preclinical drug development: does it really matter?

New treatment options for Mycobacterium abscessus infections are urgently needed. Since a correlation between MICs and clinical outcomes is not clearly established, potency of novel drugs needs to be evaluated using additional in vitro drug activity assays. Preclinical drug activity assays generally use the M. abscessus type strain ATCC 19977. However, M. abscessus complex entails a genetically and morphologically diverse group, and it is questionable whether drug activity observed against ATCC 19977 is representative of drug activity against clinical M. abscessus isolates. To assess whether the relationship between MIC and the quantitative antimycobacterial activity of amikacin, imipenem and clofazimine differs between the ATCC 19977 strain and clinical M. abscessus isolates. Experiments were performed with M. abscessus ATCC 19977 and a subset of six clinical isolates covering the three M. abscessus subspecies and the smooth and rough morphotypes. Cultures were exposed to the drugs at 4-fold increasing, MIC-standardized concentrations, and the mycobacterial load was assessed over time. Concentration- and time-dependent activity of amikacin, imipenem and clofazimine against the six clinical isolates was similar. Only slight variations in drug activity were observed between ATCC 19977 and clinical isolates. Time- and concentration-dependent drug activity against the ATCC 19977 strain seems indicative for in vitro drug behaviour against M. abscessus complex clinical isolates. Including one clinical smooth morphotype isolate alongside ATCC 19977 seems appropriate for reliable interpretation of this particular in vitro drug activity assay as part of the M. abscessus preclinical drug development pipeline.

The diversity of clinical Mycobacterium abscessus isolates in morphology, glycopeptidolipids and infection rates in a macrophage model.

Introduction. Mycobacterium abscessus (MABS) is a pathogenic bacterium that can cause severe lung infections, particularly in individuals with cystic fibrosis. MABS colonies can exhibit either a smooth (S) or rough (R) morphotype, influenced by the presence or absence of glycopeptidolipids (GPLs) on their surface, respectively. Despite the clinical significance of these morphotypes, the relationship between GPL levels, morphotype and the pathogenesis of MABS infections remains poorly understood.Gap statement. The mechanisms and implications of GPL production and morphotypes in clinical MABS infections are unclear. There is a gap in understanding their correlation with infectivity and pathogenicity, particularly in patients with underlying lung disease.Aim. This study aimed to investigate the correlation between MABS morphology, GPL and infectivity by analysing strains from cystic fibrosis patients' sputum samples.Methodology. MABS was isolated from patient sputum samples and categorized by morphotype, GPL profile and replication rate in macrophages. A high-content ex vivo infection model using THP-1 cells assessed the infectivity of both clinical and laboratory strains.Results. Our findings revealed that around 50 % of isolates displayed mixed morphologies. GPL analysis confirmed a consistent relationship between GPL content and morphotype that was only found in smooth isolates. Across morphotype groups, no differences were observed in vitro, yet clinical R strains were observed to replicate at higher levels in the THP-1 infection model. Moreover, the proportion of infected macrophages was notably higher among clinical R strains compared to their S counterparts at 72 h post-infection. Clinical variants also infected THP-1 cells at significantly higher rates compared to laboratory strains, highlighting the limited translatability of lab strain infection data to clinical contexts.Conclusion. Our study confirmed the general correlation between morphotype and GPL levels in smooth strains yet unveiled more variability within morphotype groups than previously recognized, particularly during intracellular infection. As the R morphotype is the highest clinical concern, these findings contribute to the expanding knowledge base surrounding MABS infections, offering insights that can steer diagnostic methodologies and treatment approaches.

In vitro effects of the new oral β-lactamase inhibitor xeruborbactam in combination with oral β-lactams against clinical Mycobacterium abscessus isolates.

Mycobacterium abscessus subsp. abscessus (M. abscessus) disease is treated in two phases; injectable drugs for initial followed by others for continuation. There is a need to develop all-oral treatment methods for M. abscessus infection, especially in the continuation phase. However, treatment options for M. abscessus are limited owing to their natural resistance to most antibiotics. This is the first report to evaluate the in vitro effects of xeruborbactam, a cyclic boronic acid β-lactamase inhibitor capable of inhibiting the class A β-lactamase produced by M. abscessus, against 43 M. abscessus clinical isolates when combined with five β-lactam antibiotics. Xeruborbactam lowered the MIC90 values of tebipenem by five dilutions, and the number of susceptible isolates increased from 1/43 (2%) to 43/43 (100%). We showed that the tebipenem-xeruborbactam combination might be of interest to explore further as a potentially effective oral regimen for outpatient treatment of M. abscessus pulmonary disease.

Lipoarabinomannan modification as a source of phenotypic heterogeneity in host-adapted Mycobacterium abscessus isolates

Mycobacterium abscessus is increasingly recognized as the causative agent of chronic pulmonary infections in humans. One of the genes found to be under strong evolutionary pressure during adaptation of M. abscessus to the human lung is embC which encodes an arabinosyltransferase required for the biosynthesis of the cell envelope lipoglycan, lipoarabinomannan (LAM). To assess the impact of patient-derived embC mutations on the physiology and virulence of M. abscessus, mutations were introduced in the isogenic background of M. abscessus ATCC 19977 and the resulting strains probed for phenotypic changes in a variety of in vitro and host cell-based assays relevant to infection. We show that patient-derived mutational variations in EmbC result in an unexpectedly large number of changes in the physiology of M. abscessus, and its interactions with innate immune cells. Not only did the mutants produce previously unknown forms of LAM with a truncated arabinan domain and 3-linked oligomannoside chains, they also displayed significantly altered cording, sliding motility, and biofilm-forming capacities. The mutants further differed from wild-type M. abscessus in their ability to replicate and induce inflammatory responses in human monocyte-derived macrophages and epithelial cells. The fact that different embC mutations were associated with distinct physiologic and pathogenic outcomes indicates that structural alterations in LAM caused by nonsynonymous nucleotide polymorphisms in embC may be a rapid, one-step, way for M. abscessus to generate broad-spectrum diversity beneficial to survival within the heterogeneous and constantly evolving environment of the infected human airway.

Genomic epidemiology of Mycobacterium abscessus at an adult cystic fibrosis programme reveals low potential for healthcare-associated transmission.

Nontuberculous mycobacteria (NTM) has been reported to be transmitted between people with cystic fibrosis (CF) attending CF centres. A suspected Mycobacterium abscessus outbreak was investigated at the University of Texas Southwestern (UTSW) Adult CF Program using a combination of pathogen genomic sequencing and epidemiologic methods. The objectives of the present study were to apply the Healthcare-Associated Links in Transmission of NTM (HALT NTM) study to investigate the occurrence of potential healthcare-associated transmission and/or acquisition of NTM among people with CF infected with genetically similar NTM isolates. Whole-genome sequencing of respiratory M. abscessus isolates from 50 people with CF receiving care at UTSW was performed to identify genetically similar isolates. Epidemiologic investigation, comparison of respiratory and environmental isolates, and home residence watershed mapping were studied. Whole-genome sequencing analysis demonstrated seven clusters of genetically similar M. abscessus (four ssp. abscessus and three ssp. massiliense). Epidemiologic investigation revealed potential opportunities for healthcare-associated transmission within three of these clusters. Healthcare environmental sampling did not recover M. abscessus, but did recover four human disease-causing species of NTM. No subjects having clustered infections lived in the same home residence watershed. Some subjects were infected with more than one M. abscessus genotype, both within and outside of the dominant circulating clones. Healthcare-associated person-to-person transmission of M. abscessus appears to be rare at this centre. However, polyclonal infections of M. abscessus species and subspecies, not originating from the endemic hospital environment, suggest multiple shared modes of acquisition outside the healthcare setting.

Identification of essential oils with strong activity against stationary phase Mycobacterium abscessus

PurposeTo identify essential oils (EOs) active against non-growing stationary phase Mycobacterium abscessus and multidrug-resistant M. abscessus strains. MethodsThe activity of EOs against both stationary and log phase M. abscessus was evaluated by colony forming unit (CFU) assay and minimum inhibitory concentration (MIC) testing. ResultsWe assessed the activity of 80 EOs against stationary phase M. abscessus and found 12 EOs (Cinnamon, Satureja montana, Palmarosa, Lemon eucalyptus, Honey myrtle, Combava, Health shield, Mandarin, Thyme, Rosewood, Valerian Root and Basil) at 0.5% concentration to be active against both growing and non-growing stationary phase M. abscessus. Among them, Satureja montana essential oil and Palmarosa essential oil could eliminate all stationary phase M. abscessus at 0.125% and Cinnamon essential oil could eliminate stationary phase bacteria at 0.063% after 1-day treatment. Interestingly, these EOs also exhibited promising activity against multidrug-resistant M. abscessus clinical strains. ConclusionsOur study indicates that some EOs display outstanding effectiveness against both drug susceptible M. abscessus and multidrug-resistant M. abscessus isolates. These findings may be significant for the treatment of persistent M. abscessus infections.

Rapid detection of clarithromycin resistance in clinical samples of nontuberculous mycobacteria by nucleotide MALDI-TOF MS

The multidrug resistance of nontuberculous mycobacteria (NTM) poses a significant therapeutic challenge. Rapid and reliable drug susceptibility testing is urgently needed for evidence-based treatment decision, especially for macrolides. This study evaluated the utility of nucleotide matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (NMTMS) in detecting clarithromycin resistance. Sixty-four clinical isolates were identified to species by NMTMS, and mutations associated with clarithromycin resistance were detected. Twenty-three M. abscessus (MAB) isolates and 30 M. intracellulare isolates (including M. intracellulare alone and M. intracellulare in combination with other SGM species) were included for analysis. The predictive sensitivity of NMTMS in detecting clarithromycin resistance was 82.35% (95% CI, 56.57% to 96.20%), with an AUC of 0.89 (95% CI, 0.77 to 0.96) in all MAB and M. intracellulare (n = 53), and up to 93.33% (95% CI, 68.05% to 99.83%) in MAB alone (n = 23). The assay provides a rapid, high-throughput, and highly sensitive tool for detecting clarithromycin resistance in NTM, especially in MAB. Optimization of the panel is necessary to enhance diagnostic accuracy.

Nitric oxide-releasing prodrug for the treatment of complex Mycobacterium abscessus infections.

Non-tuberculosis mycobacteria (NTM) can cause severe respiratory infection in patients with underlying pulmonary conditions, and these infections are extremely difficult to treat. In this report, we evaluate a nitric oxide (NO)-releasing prodrug [methyl tris diazeniumdiolate (MD3)] against a panel of NTM clinical isolates and as a treatment for acute and chronic NTM infections in vivo. Its efficacy in inhibiting growth or killing mycobacteria was explored in vitro alongside evaluation of the impact to primary human airway epithelial tissue. Airway epithelial tissues remained viable after exposure at concentrations of MD3 needed to kill mycobacteria, with no inherent toxic effect from drug scaffold after NO liberation. Resistance studies conducted via serial passage with representative Mycobacterium abscessus isolates demonstrated no resistance to MD3. When administered directly into the lung via intra-tracheal administration in mice, MD3 demonstrated significant reduction in M. abscessus bacterial load in both acute and chronic models of M. abscessus lung infection. In summary, MD3 is a promising treatment for complex NTM pulmonary infection, specifically those caused by M. abscessus, and warrants further exploration as a therapeutic.

Investigating a pulmonary Mycobacterium abscessus infection outbreak among elderly inpatients in the intensive care ward.

Mycobacterium abscessus is an opportunistic nontuberculous mycobacteria pathogen; however, the prevalence of nosocomial and community infections is increasing. In January 2016, several bedridden inpatients in the intensive care unit of a hospital had positive sputum smears for acid-fast bacilli, suggesting a mycobacteria outbreak. Acid-fast bacilli smear microscopy, isolation, and culturing were performed twice using sputa from each suspected intensive care unit inpatient (n = 13); in addition, medical history was obtained for each inpatient with suspected infection. Furthermore, environmental specimens were surveyed, collected, and cultured. We used DNA microarray chip analysis to identify positive mycobacterial isolates at the species level and performed whole-genome sequencing and phylogenetic tree construction. Seven inpatients had M. abscessus pulmonary infection, confirmed by 2 positive cultures; five of the inpatients had only one positive culture, while one had two negative cultures. Six of 13 ventilator condensate samples were mycobacterial culture-positive, identified as M. abscessus; the other environmental samples were negative. The M. abscessus isolates (15 sputa and 4 environmental samples) clustered together in the phylogenic analysis with only one single-nucleotide polymorphism difference. All patients were symptom-free after 8 months of multi-drug treatment. We confirmed a pulmonary M. abscessus outbreak among 12 bedridden patients in the intensive care unit through microbiological, molecular epidemiological, and environmental investigations. The possible infection source was contaminated ventilator condensate. This outbreak reemphasizes the importance of standardized ventilator maintenance and disinfection for preventing ventilator-associated pneumonia and is a reminder that nontuberculous mycobacteria-related ventilator-associated pneumonia is possible.

A cluster of three extrapulmonary Mycobacterium abscessus infections linked to well-maintained water-based heater-cooler devices.

Various water-based heater-cooler devices (HCDs) have been implicated in nontuberculous mycobacteria outbreaks. Ongoing rigorous surveillance for healthcare-associated M. abscessus (HA-Mab) put in place following a prior institutional outbreak of M. abscessus alerted investigators to a cluster of 3 extrapulmonary M. abscessus infections among patients who had undergone cardiothoracic surgery. Investigators convened a multidisciplinary team and launched a comprehensive investigation to identify potential sources of M. abscessus in the healthcare setting. Adherence to tap water avoidance protocols during patient care and HCD cleaning, disinfection, and maintenance practices were reviewed. Relevant environmental samples were obtained. Patient and environmental M. abscessus isolates were compared using multilocus-sequence typing and pulsed-field gel electrophoresis. Smoke testing was performed to evaluate the potential for aerosol generation and dispersion during HCD use. The entire HCD fleet was replaced to mitigate continued transmission. Clinical presentations of case patients and epidemiologic data supported intraoperative acquisition. M. abscessus was isolated from HCDs used on patients and molecular comparison with patient isolates demonstrated clonality. Smoke testing simulated aerosolization of M. abscessus from HCDs during device operation. Because the HCD fleet was replaced, no additional extrapulmonary HA-Mab infections due to the unique clone identified in this cluster have been detected. Despite adhering to HCD cleaning and disinfection strategies beyond manufacturer instructions for use, HCDs became colonized with and ultimately transmitted M. abscessus to 3 patients. Design modifications to better contain aerosols or filter exhaust during device operation are needed to prevent NTM transmission events from water-based HCDs.

Genetic stability of Mycobacterium abscessus during antibiotic treatment

Genetic changes in Mycobacterium abscessus during antibiotic treatment are not fully understood. This study aimed to investigate the genetic changes in M. abscessus in patients receiving antibiotic treatment, and their clinical implications. Pretreatment and 12-month post-treatment M. abscessus isolates were obtained from patients with M. abscessus pulmonary disease. Isolates from each time point were separated into six groups based on their distinctive morphological characteristics. Twenty-four isolates, comprising 12 from patient A exhibiting progressive disease and 12 from patient B demonstrating stable disease, underwent sequencing. Subsequently, minimal inhibitory concentrations (MICs) for the administered antibiotics were measured. Persistent infection with a single strain was observed in patients A and B. During 12 months of treatment, MICs for administered drugs did not generally change over time in either patient and single nucleotide variations (SNV) associated with antimicrobial resistance (rrl, rrs, erm(41), gyrA, gyrB, whiB7 and hflX) were not mutated. Although not significant, 47 and 52 non-synonymous SNVs occurred in M. abscessus from patients A and B, respectively, and the accumulation of these SNVs differed in patients A and B, except for five SNVs. The most variable positions were within a probable NADH-dependent glutamate synthase gene and a putative YrbE family protein gene in patients A and B, respectively. Persistent infections by a single strain of M. abscessus were observed in two patients with different clinical courses. Genetic changes in M. abscessus during antibiotic treatment were relatively stable in these patients. NCT01616745 (ClinicalTrials.gov ID).

Clinically relevant mutations in the PhoR sensor kinase of host-adapted Mycobacterium abscessus isolates impact response to acidic pH and virulence.

Difficult-to-treat pulmonary infections caused by nontuberculous mycobacteria of the Mycobacterium abscessus group have been steadily increasing in the USA and globally. Owing to the relatively recent recognition of M. abscessus as a human pathogen, basic and translational research to address critical gaps in diagnosis, treatment, and prevention of diseases caused by this microorganism has been lagging behind that of the better-known mycobacterial pathogen, Mycobacterium tuberculosis. To begin unraveling the molecular mechanisms of pathogenicity of M. abscessus, we here focus on the study of a two-component regulator known as PhoPR which we found to be under strong evolutionary pressure during human lung infection. We show that PhoPR is activated at acidic pH and serves to regulate a defined set of genes involved in host adaptation. Accordingly, clinical isolates from chronically infected human lungs tend to hyperactivate this regulator enabling M. abscessus to escape macrophage killing.

Intraspecific Diversity of <i>Mycobacterium abscessus</i> Isolated from Patients with Pulmonary Lesions

The objective: to perform intraspecific differentiation of M. abscessus strains isolated from patients with pulmonary lesions using molecular genetic tests.Results. Intraspecific differentiation of 164 cultures of M. abscessus from 114 patients without cystic fibrosis showed that the subspecies M. abscessus subsp. dominated in the analysis set (90 of 114 patients; 78,95%), followed by M. abscessus subsp. massiliense (24/114; 21,05%). In 54 examined cystic fibrosis patients excreting non-tuberculous mycobacteria, M. abscessus was most often detected (41 patients out of 54; 75,93%). Intraspecific identification of the obtained M. abscessus isolates demonstrated the prevalence of the subspecies M. abscessus subsp. abscessus (29/41; 70,73%) over M. abscessus subsp. massiliense (11/41; 26,83%). In one case, a rare M. abscessus subsp. bolletii (1/41; 2,44%) was detected.

In vitro susceptibility testing of imipenem-relebactam and tedizolid against 102 Mycobacterium abscessus isolates

Mycobacterium abscessus is an emerging infection in people living with lung diseases including cystic fibrosis (CF) and bronchiectasis and has limited treatment options and low cure rates. The off-label use of novel antibiotics developed for other bacterial pathogens offers potential new therapeutic options. We aimed to describe the in vitro activity of imipenem, imipenem-relebactam and tedizolid against comparator antibiotics in M. abscessus isolates from Australian patients with and without CF. Susceptibility testing was performed by Clinical and Laboratory Standards Institute (CLSI) criteria against 102 clinical M. abscessus isolates including 46 from people with CF. The minimum inhibitory concentration (MICs) of imipenem-relebactam was 1-fold dilution less than of imipenem alone. The MIC50 and MIC90 of imipenem-relebactam was 8 and 16 mg/L respectively while for imipenem they were 16 and 32 mg/L. Tedizolid had an MIC50 and MIC90 of 2 and 4 mg/L, respectively. Forty non-CF isolates had linezolid susceptibility performed, with MIC50 and MIC90 values of 16 and 32 mg/L, respectively, measured. This study supports the consideration of imipenem-relebactam and tedizolid in clinical trials for M. abscessus treatment.

Omadacycline, Eravacycline, and Tigecycline Express Anti-Mycobacterium abscessus Activity In Vitro.

Mycobacterium abscessus infections are increasing worldwide necessitating the development of new antibiotics and treatment regimens. The utility of third-generation tetracycline antibiotics was reestablished; their anti-M. abscessus activity needs further study. The activities of omadacycline (OMC), eravacycline (ERC), tigecycline (TGC), and sarecycline (SAC) were tested against two reference strains and 193 clinical M. abscessus isolates at different temperatures (30°C and 37°C). The minimum bactericidal concentrations (MBCs) of the four drugs were determined to distinguish between their bactericidal and bacteriostatic activities. The MICs of OMC, ERC, and TGC for the reference strains and clinical isolates were summarized and compared. OMC, ERC, and TGC exhibited a high level of bacteriostatic activity against M. abscessus. The MICs of OMC and ERC for M. abscess remained stable, while the MICs of TGC for the isolates/strains increased with increasing temperature. Notably, the MICs of OMC for M. abscessus isolates obtained in the United States are lower than for those obtained in China. IMPORTANCE The antimicrobial activities of four third-generation tetracycline-class drugs, omadacycline (OMC), eravacycline (ERC), tigecycline (TGC), and sarecycline (SAC), were determined for 193 M. abscessus isolates. The activities of the four drugs at two different temperatures (30°C and 37°C) were also tested. OMC, ERC, and TGC exhibited significant activity against M. abscessus. The anti-M. abscessus activity of TGC increased when the temperature was increased from 30°C to 37°C; the activities of OMC and ERC, on the other hand, remained the same. We found that in vitro MICs of OMC against Chinese and American isolates were distinct. Evaluations in in vivo models of M. abscessus disease or in the clinical setting will provide more accurate insight into potency of OMC against distinct isolates.

Efficacy of Omadacycline-Containing Regimen in a Mouse Model of Pulmonary Mycobacteroides abscessus Disease.

Mycobacteroides abscessus is an opportunistic pathogen in people with structural lung conditions such as bronchiectasis, chronic obstructive pulmonary disease, and cystic fibrosis. Pulmonary M. abscessus infection causes progressive symptomatic and functional decline as well as diminished lung function and is often incurable with existing antibiotics. We investigated the efficacy of a new tetracycline, omadacycline, in combination with existing antibiotics recommended to treat this indication, in a mouse model of M. abscessus lung disease. Amikacin, azithromycin, bedaquiline, biapenem, cefoxitin, clofazimine, imipenem, linezolid, and rifabutin were selected as companions to omadacycline. M. abscessus burden in the lungs of mice over a 4-week treatment duration was considered the endpoint. Omadacycline in combination with linezolid, imipenem, cefoxitin, biapenem, or rifabutin exhibited early bactericidal activity compared to any single drug. Using three M. abscessus isolates, we also determined the in vitro frequency of spontaneous resistance against omadacycline to be between 1.9 × 10-10 and 6.2 × 10-10 and the frequency of persistence against omadacycline to be between 5.3 × 10-6 and 1.3 × 10-5. Based on these findings, the combination of omadacycline and select drugs that are included in the recent treatment guidelines may exhibit improved potency to treat M. abscessus lung disease. IMPORTANCE M. abscessus disease incidence is increasing in the United States. This disease is difficult to cure with existing antibiotics. In this study, we describe the efficacy of a new tetracycline antibiotic, omadacycline, in combination with an existing antibiotic to treat this disease. A mouse model of M. abscessus lung disease was used to assess the efficacies of these experimental treatment regimens. Omadacycline in combination with select existing antibiotics exhibited bactericidal activity during the early phase of treatment.

Unusual prophages in Mycobacterium abscessus genomes and strain variations in phage susceptibilities.

Mycobacterium abscessus infections are relatively common in patients with cystic fibrosis and are clinically challenging, with frequent intrinsic resistance to antibiotics. Therapeutic treatment with bacteriophages offers some promise but faces many challenges including substantial variation in phage susceptibilities among clinical isolates, and the need to personalize therapies for individual patients. Many strains are not susceptible to any phages or are not efficiently killed by lytic phages, including all smooth colony morphotype strains tested to-date. Here, we analyze a set of new M. abscessus isolates for the genomic relationships, prophage content, spontaneous phage release, and phage susceptibilities. We find that prophages are common in these M. abscessus genomes, but some have unusual arrangements, including tandemly integrated prophages, internal duplications, and they participate in active exchange of polymorphic toxin-immunity cassettes secreted by ESX systems. Relatively few strains are efficiently infected by any mycobacteriophages, and the infection patterns do not reflect the overall phylogenetic relationships of the strains. Characterization of these strains and their phage susceptibility profiles will help to advance the broader application of phage therapies for NTM infections.