Liposomal amikacin and Mycobacterium abscessus: intimate interactions inside eukaryotic cells

Advances in lipid-based nanoformulations for inhaled antibiotic therapy in respiratory infections

Inhaled antibiotics significantly impact respiratory-disorder management through targeted delivery with reduced systemic side effects. Advances in pharmaceutical formulations, particularly lipid-based nanomedicine, help improve biopharmaceutical performance and therapeutic efficacy. In addition, advancements in inhaler technologies ensure effective lung deposition and minimize systemic exposure. These innovations have further benefited chronic respiratory diseases like cystic fibrosis and COPD, where infections are frequent. For instance, the encapsulation of inhaled antibiotics, particularly the tobramycin liposomal system, has improved efficacy and reduced toxicity, whereas the nebulized colistin nanoformulation effectively targets multidrug-resistant pathogens, including the clinical efficacy of amikacin liposome inhalation in refractory pulmonary infections. Overall, advancements in lipid-based nanoformulation and delivery technologies have significantly enhanced the utility of inhaled antibiotics, providing safer and more-effective options for managing chronic and resistant infections.

The complexities of elexacaftor/tezacaftor/ivacaftor therapeutic drug monitoring in a person with cystic fibrosis and Mycobacterium abscessus pulmonary disease

Therapeutic drug monitoring (TDM) of elexacaftor/tezacaftor/ivacaftor (ETI) remains challenging due to a lack of clarity around the parameters that govern ETI plasma concentrations, whilst the use of concomitant CYP3A inducers rifabutin and rifampicin is not recommended. We present the complexities of TDM for ETI performed in a person with cystic fibrosis and refractory Mycobacterium abscessus pulmonary disease. Utilising National Association of Testing Authorities (NATA) accredited assays and target considerations published by the Therapeutic Goods Administration (TGA), Australia, ETI plasma concentration variability was monitored over the course of an acute admission with added complexity from an antibiotic regimen including rifabutin, a moderate cytochrome P450 3A (CYP3A) inducer, and clofazimine, a mild CYP3A inhibitor. This case highlights the challenges surrounding ETI TDM in the context of acute severe illness, malnutrition, chronic infection, and drug-to-drug interactions. The marked clinical improvement seen, alongside sustained ETI plasma concentrations and suppressed sweat chloride levels on serial testing, provided reassurance of the use of ETI and rifabutin concomitantly in this case, and highlights the potential utility of TDM in helping guide clinical practice. Though a current barrier to the application of TDM includes ETI only being available as a fixed dose combination.

Lsr2, a pleiotropic regulator at the core of the infectious strategy of Mycobacterium abscessus

Mycobacterium abscessus is a non-tuberculous mycobacterium, causing lung infections in cystic fibrosis patients. During pulmonary infection, M. abscessus switches from smooth (Mabs-S) to rough (Mabs-R) morphotypes, the latter being hyper-virulent. Previously, we isolated the lsr2 gene as differentially expressed during S-to-R transition. lsr2 encodes a pleiotropic transcription factor that falls under the superfamily of nucleoid-associated proteins. Here, we used two functional genomic methods, RNA-seq and chromatin immunoprecipitation-sequencing (ChIP-seq), to elucidate the molecular role of Lsr2 in the pathobiology of M. abscessus. Transcriptomic analysis shows that Lsr2 differentially regulates gene expression across both morphotypes, most of which are involved in several key cellular processes of M. abscessus, including host adaptation and antibiotic resistance. These results were confirmed through quantitative real-time PCR, as well as by minimum inhibitory concentration tests and infection tests on macrophages in the presence of antibiotics. ChIP-seq analysis revealed that Lsr2 extensively binds the M. abscessus genome at AT-rich sequences and appears to form long domains that participate in the repression of its target genes. Unexpectedly, the genomic distribution of Lsr2 revealed no distinctions between Mabs-S and Mabs-R, implying more intricate mechanisms at play for achieving target selectivity.IMPORTANCELsr2 is a crucial transcription factor and chromosome organizer involved in intracellular growth and virulence in the smooth and rough morphotypes of Mycobacterium abscessus. Using RNA-seq and chromatin immunoprecipitation-sequencing (ChIP-seq), we investigated the molecular role of Lsr2 in gene expression regulation along with its distribution on M. abscessus genome. Our study demonstrates the pleiotropic regulatory role of Lsr2, regulating the expression of many genes coordinating essential cellular and molecular processes in both morphotypes. In addition, we have elucidated the role of Lsr2 in antibiotic resistance both in vitro and in vivo, where lsr2 mutant strains display heightened sensitivity to antibiotics. Through ChIP-seq, we reported the widespread distribution of Lsr2 on M. abscessus genome, revealing a direct repressive effect due to its extensive binding on promoters or coding sequences of its targets. This study unveils the significant regulatory role of Lsr2, intricately intertwined with its function in shaping the organization of the M. abscessus genome.

Synthesis and Biological Characterization of Fluorescent Cyclipostins and Cyclophostin Analogues: New Insights for the Diagnosis of Mycobacterial-Related Diseases

Patients with cystic fibrosis (CF) have a significantly higher risk of acquiring nontuberculous mycobacteria infections, predominantly due to Mycobacterium abscessus, than the healthy population. Because M. abscessus infections are a major cause of clinical decline and morbidity in CF patients, improving treatment and the detection of this mycobacterium in the context of a polymicrobial culture represents a critical component to better manage patient care. We report here the synthesis of fluorescent Dansyl derivatives of four active cyclipostins and cyclophostin analogues (CyCs) and provide new insights regarding the CyC's lack of activity against Gram-negative and Gram-positive bacteria, and above all into their mode of action against intramacrophagic M. abscessus cells. Our results pointed out that the intracellularly active CyC accumulate in acidic compartments within macrophage cells, that this accumulation appears to be essential for their delivery to mycobacteria-containing phagosomes, and consequently, for their antimicrobial effect against intracellular replicating M. abscessus, and that modification of such intracellular localization via disruption of endolysosomal pH strongly affects the CyC accumulation and efficacy. Moreover, we discovered that these fluorescent compounds could become efficient probes to specifically label mycobacterial species with high sensitivity, including M. abscessus in the presence several other pathogens like Pseudomonas aeruginosa and Staphylococcus aureus. Collectively, all present and previous data emphasized the therapeutic potential of unlabeled CyCs and the attractiveness of the fluorescent CyC as a potential new efficient diagnostic tool to be exploited in future diagnostic developments against mycobacterial-related infections, especially against M. abscessus.