Comparison of the in vitro activity of linezolid, tedizolid, sutezolid, and delpazolid against rapidly growing mycobacteria isolated in Beijing, China

Facile green synthesis of silver nanoparticles derived from the medicinal plant Clerodendrum serratum and its biological activity against Mycobacterium species

The emergence of multidrug-resistant mycobacterial strains is a significant crisis that has led to higher treatment failure rates and more toxic and expensive medications for tuberculosis (TB). The urgent need to develop novel therapeutics has galvanized research interest towards developing alternative antimicrobials such as silver nanoparticles (AgNPs). The current study focused on the anti-mycobacterial activity of green-synthesized AgNPs and its polyethylene glycol encapsulated derivative (PEG-AgNPs) with improved stability using the leaves extract of Clerodendrum serratum. Different characterization methods were used to analyze them. DLS analysis revealed a lower polydispersity index of PEG-AgNPs, suggesting a more uniform size distribution than that of AgNPs. The HR-TEM results revealed that the AgNPs and PEG-AgNPs have predominantly spherical shapes in the size range of 9-35 nm and 15-60 nm, respectively, while positive values of Zeta potential indicate their stability. FTIR-ATR analysis confirmed the presence of functional groups responsible for reducing and capping the bio-reduced AgNPs, whereas the XRD data established its crystalline nature. Impressively, the PEG-AgNPs exhibited maximum inhibitory activity against different Tubercular and Non-Tuberculous Mycobacterium species i.e., Mycobacterium smegmatis, Mycobacterium fortuitum and Mycobacterium marinum, relative to those of AgNPs and Linezolid. The flow cytometry assay showed that the anti-mycobacterial action was mediated by an increase in cell wall permeability. Notably, the results of AFM confirm their ability to inhibit mycobacterial biofilm significantly. We demonstrated the nontoxic nature of these AgNPs, explicated by the absence of hemolytic activity against human RBCs. Overall, the results suggest that PEG-AgNPs could offer a novel therapeutic approach with potential anti-mycobacterial activity and can overcome the limitations of existing TB therapies.

Treatment Approaches to Mycobacterium abscessus Pulmonary Disease

Mycobacterium abscessus pulmonary disease is highly antibiotic-resistant, and the current armamentarium of antibiotics yields poor treatment outcomes with significant drug toxicity. Macrolide susceptibility is a key prognostic factor. Optimal drug combinations, duration of therapy, and management of refractory disease are unknown. Surgical resection, performed at centers with experience in surgical management of nontuberculous mycobacterial pulmonary disease, may produce favorable outcomes in select patients. Multiple emerging therapeutic candidates hold promise for more efficacious and tolerable treatment options.

Intracellular and in vivo activities of oxazolidinone drugs against Mycobacterium avium complex infection

The prevalence of Mycobacterium avium complex-pulmonary disease (MAC-PD) has become a growing concern worldwide, and current treatments involving macrolides (clarithromycin [CLR] or azithromycin), ethambutol, and rifampicin have limited success, highlighting the need for better therapeutic strategies. Recently, oxazolidinone drugs have been identified as novel anti-tuberculosis drugs effective against drug-resistant M. tuberculosis. However, the effects of these drugs against MAC are still controversial due to limited data. Here, we first evaluated the intracellular anti-MAC activities of two oxazolidinone drugs, linezolid (LZD) and delpazolid (DZD), against 10 macrolide-susceptible MAC strains and one macrolide-resistant M. avium strain in murine bone marrow-derived macrophages (BMDMs) and found that both drugs demonstrated similar potential. The synergistic efficacies with CLR were then determined in a chronic progressive MAC-PD murine model by initiating a 4-week treatment at 8 weeks post-infection. Upon assessment of bacterial burdens and inflamed lesions, oxazolidinone drugs exhibited no anti-MAC effect, and there was no significant difference in the synergistic effect of CLR between LZD and DZD. These findings suggest that oxazolidinone drugs inhibit intracellular bacterial growth, even against macrolide-resistant MAC, but their clinical application requires further consideration.

Non-tuberculous mycobacterial disease: progress and advances in the development of novel candidate and repurposed drugs

Non-tuberculous mycobacteria (NTM) are opportunistic pathogens that can infect all body tissues and organs. In particular, the lungs are the most commonly involved organ, with NTM pulmonary diseases causing serious health issues in patients with underlying lung disease. Moreover, NTM infections have been steadily increasing worldwide in recent years. NTM are also naturally resistant to many antibiotics, specifically anti-tuberculosis (anti-TB) drugs. The lack of drugs targeting NTM infections and the increasing drug resistance of NTM have further made treating these mycobacterial diseases extremely difficult. The currently recommended NTM treatments rely on the extended indications of existing drugs, which underlines the difficulties of new antibiotic discovery against NTM. Another challenge is determining which drug combinations are most effective against NTM infection. To a certain extent, anti-NTM drug development depends on using already available antibiotics and compounds. Here, we aimed to review new antibiotics or compounds with good antibacterial activity against NTM, focusing on their mechanisms of action, in vitro and in vivo antibacterial activities.

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

OBJECTIVES

Mycobacterium abscessus is an emerging infection in people living with lung diseases, including cystic fibrosis (CF) and bronchiectasis, and it 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.

METHODS

We performed susceptibility testing for imipenem-relebactam, tedizolid and comparator antibiotics by Clinical and Laboratory Standards Institute (CLSI) criteria against 102 clinical M. abscessus isolates, including 46 from people with CF.

RESULTS

In this study, the minimum inhibitory concentration (MICs) of imipenem-relebactam was one-fold dilution less than of imipenem alone. The MIC50 and MIC90 of imipenem-relebactam were 8 and 16 mg/L, respectively, whereas 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.

CONCLUSIONS

This study shows lower MICs for imipenem-relebactam and tedizolid compared to other more commonly used antibiotics and supports their consideration in clinical trials for M. abscessus treatment.

Characterization of In Vitro Resistance to Linezolid in Mycobacterium abscessus

Single-step selection of Mycobacterium abscessus mutants resistant to linezolid yielded high-level resistance at a low frequency that was associated with mutations in 23S rRNA or the ribosomal protein L3. Surprisingly, linezolid-resistant rRNA mutations conferred cross-resistance to several unrelated antibiotics. Low-level linezolid-resistant mutants were isolated at a higher frequency and were due to loss-of-function mutations in the transcriptional regulator MAB_4384, the repressor of the drug efflux pump MmpL5-MmpS5. IMPORTANCE The protein synthesis inhibitor linezolid is used for the treatment of lung disease caused by Mycobacterium abscessus. However, many strains of the bacterium show poor susceptibility to the antibiotic. For most clinical isolates, resistance is not due to mutations in the target of the drug, the ribosome. The mechanism responsible for non-target-related, indirect linezolid resistance is unknown. Here, we analyzed the development of linezolid resistance in the M. abscessus reference strain in vitro. We found, as expected, resistance mutations in the ribosome. In addition, we identified mutations in a system that involves a drug pump, suggesting drug efflux as a mechanism of resistance to linezolid. This finding may inform the analysis of clinical resistance to linezolid. Surprisingly, a subset of linezolid-resistant ribosome mutations conferred cross-resistance to several structurally and mechanistically unrelated drugs, uncovering a novel multidrug resistance mechanism.

Skin and soft tissue infections due to rapidly growing mycobacteria

PURPOSE OF REVIEW

The aim of this article is to review skin and soft tissue infections due to rapidly growing mycobacteria (RGM), with a particular focus on recently published literature (2021-2022).

RECENT FINDINGS

RGM are increasingly reported as a cause of skin and soft tissue infections, both in the community setting and as a cause of nosocomial outbreaks. Recent advances in molecular methods have expanded the number of species of RGM and resulted in increased diagnosis. New treatment options are under evaluation particularly for Mycobacterium abscessus , the most difficult-to-treat among RGM.

SUMMARY

RGM are an uncommon cause of skin and soft tissue infections and a high clinical suspicion together with advanced laboratory facilities are required for diagnosis. Species identification and antimicrobial susceptibility testing are essential to drive appropriate treatment, which combines surgical debridement with prolonged antimycobacterial combination therapy.

Contemporary Pharmacotherapies for Nontuberculosis Mycobacterial Infections: A Narrative Review

Nontuberculous mycobacteria (NTM) are a group of atypical bacteria that may cause a spectrum of clinical manifestations, including pulmonary, musculoskeletal, skin and soft tissue, and cardiac infections. Antimycobacterial medication regimens for NTM infections require multiple agents with prolonged treatment courses and are often associated with poor tolerance in patients and suboptimal clinical outcomes. This review summarizes NTM pharmacotherapy, including treatment concepts, preferred medication regimens according to NTM species and site of infection, and emerging treatment methods for difficult-to-treat species.

Antimicrobial Effect of Oxazolidinones and Its Synergistic Effect with Bedaquiline Against Mycobacterium abscessus Complex

Purpose

Unsatisfactory efficacies of currently recommended anti-Mycobacterium abscessus complex (MABC) treatment regimens have led to development of novel drugs to combat MABC infections. In this study, we evaluated in vitro antimicrobial activities of bedaquiline (BDQ) and four oxazolidinones against MABC isolates.

Methods

The resazurin microplate assay was performed to determine minimum inhibitory concentrations (MICs) of BDQ and four oxazolidinones, including tedizolid (TZD), sutezolid (SZD), delpazolid (DZD), and linezolid (LZD), against 65 MABC isolates. A checkerboard method was used to investigate efficacies of various antimicrobial drug combinations.

Results

BDQ MICs for MABC isolates ranged from <0.031 to 1 µg/mL, while MIC₅₀ and MIC₉₀ values were 0.125 µg/mL and 0.25 µg/mL, respectively. TZD MIC₅₀ and MIC₉₀ values for MABC isolates were 1 µg/mL and 4 µg/mL, respectively, which were fourfold lower than corresponding LZD values (P < 0.001). DZD MIC₉₀ values for MABC isolates was 8 µg/mL, which were 0.5-fold lower than corresponding LZD values (P < 0.01). MICs of BDQ, SZD, and LZD for M. abscessus subspecies massiliense isolates were significantly lower than corresponding MICs for M. abscessus subspecies abscessus isolates (P < 0.05). Notably, use of oxazolidinones (DZD, SZD, LZD, or TZD) with BDQ against MABC isolates led to reduction of the oxazolidinone median MIC range from 4 to 0.125 µg/mL to 1-0.031 µg/mL.

Conclusion

These results demonstrated excellent BDQ inhibitory activity against MABC isolates. TZD exhibited stronger antimicrobial efficacy against MABC isolates as compared to efficacies of DZD, SZD, and LZD. Importantly, MICs of oxazolidinones were markedly decreased when they were combined with BDQ, thus suggesting that combinations of BDQ and oxazolidinones may be effective treatments for MABC infections.

Epidemiology of Nontuberculous Mycobacteria in Nanjing and MAB_0540 Mutations Associated with Clofazimine Resistance in Mycobacterium abscessus

Background

Nontuberculous mycobacteria (NTM) are easily misdiagnosed as multidrug-resistant tuberculosis (MDR-TB), and treatment drugs are very limited. The main objective of our study was to evaluate the minimal inhibitory concentration (MIC) in vitro of bedaquiline (BDQ), clofazimine (CFZ), linezolid (LZD), delamanid (DLM), and pretomanid (PA-824) for treatment of M. abscessus and M. intracellulare. Furthermore, we determined whether MAB_1448, MAB_4384, MAB_2299c, MAB_1483, MAB_0540, rplD, rplC, and rrl were related to drug resistance to provide an experimental basis for the use of these five drugs in the treatment of NTM.

Methods

We identified sample characteristics of epidemics in 550 patients with suspected NTM infection in Nanjing from 2019 to 2021 using the PCR-reverse spot hybrid method. Furthermore, we evaluated the MIC of BDQ, CFZ, DLM, LZD, and PA-824 against 155 clinical isolates of NTM using the microbroth dilution method. The resistant isolates were sequenced using Sanger sequencing.

Results

The top three dominant species of NTM distributed in Nanjing were M. intracellulare, M. avium, and M. abscessus. Notably, the proportion of M. abscessus infections increased. The proportion of M. abscessus increased from 12% in 2019 to 18% in 2021. Demographic analysis showed that female infection rates were substantialy greater than male for M. abscessus (P=0.017, <0.05). Our results demonstrate that NTM are highly sensitive to bedaquiline and clofazimine in vitro. However, delamanid and pretomanid had little effect on M. abscessus and M. intracellulare. In addition, we found 30-41 nucleotide deletion mutations and some novel point mutations in the MAB_0540 gene of M. abscessus that are resistant to clofazimine.

Conclusion

Bedaquiline, clofazimine, and linezolid were more successful in vitro treatments against M. abscessus and M. intracellulare. The MAB_0540 mutation may be associated with resistance of M. abscessus to clofazimine.

The Struggle to End a Millennia-Long Pandemic: Novel Candidate and Repurposed Drugs for the Treatment of Tuberculosis

This article provides an encompassing review of the current pipeline of putative and developed treatments for tuberculosis, including multidrug-resistant strains. The review has organized each compound according to its site of activity. To provide context, mention of drugs within current recommended treatment regimens is made, thereafter followed by discussion on recently developed and upcoming molecules at established and novel targets. The review is designed to provide a clinically applicable understanding of the compounds that are deemed most currently relevant, including those already under clinical study and those that have shown promising pre-clinical results. An extensive review of the efficacy and safety data for key contemporary drugs already incorporated into treatment regimens, such as bedaquiline, pretomanid, and linezolid, is provided. The three levels of the bacterial cell wall (mycolic acid, arabinogalactan, and peptidoglycan layers) are highlighted and important compounds designed to target each layer are delineated. Amongst others, the highly optimistic and potent anti-mycobacterial activity of agents such as BTZ-043, PBTZ 169, and OPC-167832 are emphasized. The evolving spectrum of oxazolidinones, such as sutezolid, delpazolid, and TBI-223, all aiming to exceed the efficacy achieved with linezolid yet offer a safer alternative to the potential toxicity, are reviewed. New and exciting prospective agents with novel mechanisms of impact against TB, including 3-aminomethyl benzoxaboroles and telacebec, are underscored. We describe new diaryloquinolines in development, striving to build on the immense success of bedaquiline. Finally, we discuss some of these compounds that have shown encouraging additive or synergistic benefit when used in combination, providing some promise for the future in treating this ancient scourge.

In vitro Susceptibility of Nontuberculous Mycobacteria to Tedizolid

Objective

Nontuberculous mycobacteria (NTM) can cause pulmonary and extrapulmonary diseases. Tedizolid (TZD) is a new oxazolidinone with in vitro activity against NTM such as Mycobacterium avium complex (MAC), Mycobacterium fortuitum, and Mycobacterium abscessus complex. The aim of this study was to evaluate the TZD susceptibility profiles of clinical isolates of NTM.

Methods

The microdilution method was used to identify the minimum inhibitory concentration (MIC) of TZD and linezolid (LZD) for 133 clinical NTM isolates. Broth microdilution chequerboard assays were used to investigate the synergistic effects of TZD and three antibiotics on two reference isolates and eleven clinical isolates of NTM.

Results

The TZD MIC₅₀ and MIC₉₀ for M. abscessus complex were 2 and 4 μg/mL, 16 and >32 μg/mL for MAC, respectively. TZD exhibited lower MICs than that of LZD for most NTM, which were positively correlated. Due to the high MIC values of TZD against MAC, it is necessary to conduct drug sensitivity tests before TZD administration. TZD-clarithromycin combination had synergistic response on M. abscessus complex in 3 of the 8 isolates, which lasted only 3-5 days. TZD-cefoxitin had synergistic effect against all five M. fortuitum isolates.

Conclusion

Our study demonstrates that TZD had greater in vitro potency than LZD, and synergy studies suggested that TZD may be an important component of multi-drug treatment regimen.

New RAPMYCOI SensititreTM Antimicrobial Susceptibility Test for Atypical Rapidly Growing Mycobacteria (RGM)

Rapidly growing mycobacteria (RGM) cause an increasing international concern, mainly due to their natural resistance to many antibiotics. The aim of this study was to conduct species identification and determine the antimicrobial susceptibility profiles of RGM isolated in Poland. Antimicrobial susceptibility was tested using broth microdilution and the RAPMYCOI panel. A total of 60 strains were analysed, including the following species: M. fortuitum complex (30), M. abscessus subsp. abscessus (16), M. abscessus subsp. massiliense (7), M. chelonae (5), and M. mucogenicum (2). For 12 M. abscessus subsp. abscessus strains, the presence of the erm 41T28 genotype associated with inducible macrolide resistance and a functional erm gene was confirmed. A MUT2 mutation in the rrl gene (constitutive resistance) was identified for two strains from the subtype M. abscessus subsp. massiliense. Among the 15 tested antibiotics, amikacin and linezolid had the strongest antimycobacterial activity. Most of the tested strains were resistant to doxycycline and trimethoprim/sulfamethoxazole. Tigecycline MICs were low for all tested strains. Findings from our study highlight the importance of correct identification of clinical isolates and antimicrobial susceptibility testing.

MDR Tuberculosis Treatment

Multidrug-resistant (MDR) tuberculosis (TB), resistant to isoniazid and rifampicin, continues to be one of the most important threats to controlling the TB epidemic. Over the last few years, there have been promising pharmacological advances in the paradigm of MDR TB treatment: new and repurposed drugs have shown excellent bactericidal and sterilizing activity against Mycobacterium tuberculosis and several all-oral short regimens to treat MDR TB have shown promising results. The purpose of this comprehensive review is to summarize the most important drugs currently used to treat MDR TB, the recommended regimens to treat MDR TB, and we also summarize new insights into the treatment of patients with MDR TB.

Inhibition of chloroplast translation as a new target for herbicides

The rise in herbicide resistance over recent decades threatens global agriculture and food security and so discovery of new modes of action is increasingly important. Here we reveal linezolid, an oxazolidinone antibiotic that inhibits microbial translation, is also herbicidal. To validate the herbicidal mode of action of linezolid we confirmed its micromolar inhibition is specific to chloroplast translation and did not affect photosynthesis directly. To assess the herbicide potential of linezolid, testing against a range of weed and crop species found it effective pre- and post-emergence. Using structure-activity analysis we identified the critical elements for herbicidal activity, but importantly also show, using antimicrobial susceptibility assays, that separation of antibacterial and herbicidal activities was possible. Overall these results validate chloroplast translation as a viable herbicidal target.

In vitro Antimicrobial Activity Comparison of Linezolid, Tedizolid, Sutezolid and Delpazolid Against Slowly Growing Mycobacteria Isolated in Beijing, China

Background

The antimicrobial activities of some new oxazolidinones against slowly growing mycobacteria (SGM) have never been well evaluated.

Methods

We evaluate the in vitro susceptibility of 20 reference strains and 157 clinical isolates, pertaining different SGM species, against four oxazolidinones, ie, delpazolid, sutezolid, tedizolid and linezolid. In addition, the association of linezolid resistance and mutations in 23srRNA, rplC, rplD were also tested.

Results

Sutezolid presented the strongest antimicrobial activity against the clinical isolates of M. intracellulare than the other oxazolidinones, with MIC₅₀ at 2 μg/mL and MIC₉₀ at 4 μg/mL. MICs of sutezolid were usually 4- to 8-fold lower than these of linezolid against M. intracellulare and M. avium. The tested isolates of M. kansasii were susceptible to all of the four oxazolidinones. According to the multiple sequence alignment, novel 23srRNA mutations (A2267C and A2266G) in M. intracellulare and rplD mutations (Thr147Ala) in M. avium were identified in this study which have plausible involvement in rendering resistance against linezolid.

Conclusion

This study showed that sutezolid harbors the strongest inhibitory activity against M. intracellulare, M. avium and M. kansasii in vitro, which provided important insights on the potential clinical application of oxazolidinones for treating SGM infections.

Current Molecular Therapeutic Agents and Drug Candidates for Mycobacterium abscessus

Mycobacterium abscessus has been recognised as a dreadful respiratory pathogen among the non-tuberculous mycobacteria (NTM) because of misdiagnosis, prolonged therapy with poor treatment outcomes and a high cost. This pathogen also shows extremely high antimicrobial resistance against current antibiotics, including the anti-tuberculosis agents. Therefore, current chemotherapies require a long curative period and the clinical outcomes are not satisfactory. Thus, there is an urgent need for discovering and developing novel, more effective anti-M. abscessus drugs. In this review, we sum the effectiveness of the current anti-M. abscessus drugs and drug candidates. Furthermore, we describe the shortcomings and difficulties associated with M. abscessus drug discovery and development.