Amikacin exposure and susceptibility of macrolide-resistant Mycobacterium abscessus

Drug susceptibility profiles of Mycobacterium abscessus isolated in the state of São Paulo, 2008-2024

Introduction. Infections caused by Mycobacterium abscessus, an environmentally prevalent, rapidly growing mycobacteria, are increasingly frequent in developed countries.Objective. To analyse the drug susceptibility profiles of M. abscessus isolated in the state of São Paulo from 2008 to 2024.Methods. Of the 2,402 M. abscessus isolates identified during those 17 years, 558 (23.2%) met the American Thoracic Society's microbiologic and clinical criteria for drug susceptibility testing (DST), which was performed for five agents - clarithromycin, amikacin, cefoxitin, ciprofloxacin, and doxycycline.Results. Clarithromycin showed a dramatic increase in resistance phenotype from ≤10% in the early period to 73-90% over the last 8 years. Over half those isolates demonstrated inducible resistance. Resistance to amikacin was found in fewer than 5% of isolates from 2016 to 2021. In 2022, that result increased to 13%, but for 2023 and 2024, it had fallen back to 2%. Over the past decade, cefoxitin DST has reported the majority of isolates as intermediate, a problematic result in M. abscessus group (MAG) infections, which typically require long-term treatment for successful outcomes. Since 2018, the annual susceptibility rate has been ≤18%, and in five of the 7 years, ≤7%. Ciprofloxacin was typically assessed as susceptible from 2009 to 2011, then decreased sharply to ≤20% over the next several years, and since 2018, the rate has been less than 5%. Through the entire study, doxycycline resistance has remained consistently high; in the years since 2018, ≤6% of isolates have been susceptible.Conclusion. This study demonstrates wide variation among MAG clinical isolates in the frequency of susceptibility, both across different agents and within individual agents over time. These results emphasize the importance of performing high-quality DST on MAG clinical isolates and suggest the need to consider revising the standard panel of drugs tested.

Genetic variations underlying aminoglycoside resistance in antibiotic-induced Mycobacterium intracellulare mutants

Mycobacterium avium complex (MAC) is an emerging pathogen leading to public health concerns in developing and developed countries, particularly among immunocompromised individuals and patients with structural lung diseases. Current clinical guidelines recommend combination antibiotic therapy for treating MAC pulmonary disease (MAC-PD). However, the rising prevalence of antibiotic resistance poses significant challenges, including treatment failure and clinical recurrence. A deeper understanding of the mechanisms underlying MAC antibiotic resistance is essential to improve treatment outcomes. This study investigates the genetic variations associated with aminoglycoside resistance in an antibiotic-induced Mycobacterium intracellulare mutant derived from a clinical strain. Whole-genome analysis identified seven mutations in the aminoglycoside-resistant mutant, including single nucleotide polymorphisms (SNPs) and insertions/deletions (InDels). Key genetic alterations included a frameshift variant in a gene encoding a secreted protein antigen, missense mutations in rpsL and rsmG, and synonymous and in-frame deletion variants in srfAB and mtrB, respectively. These findings highlight the complex genetic landscape of aminoglycoside resistance in M. intracellulare. Understanding these resistance determinants provides valuable insights for developing diagnostic tools to detect drug-resistant MAC strains and optimizing therapeutic strategies for managing MAC infections in clinical practice.

Mycobacterium abscessus skin and soft tissue infection following autologous fat grafting in Kurdistan treated with an antibiotic combination including Imipenem-Relebactam and Rifabutin

Medical tourism is becoming increasingly popular. The most popularly sought operations are cosmetic procedures. With the increase in cosmetic tourism, it is unsurprising that there has also been a rise in skin and soft tissue infections caused by nontuberculous mycobacteria (NTM); in particular by the rapidly growing mycobacteria species. Here we provide a case of a 35 year-old woman who presented after autologous fat grafting with multiple painful, violaceous, and purulent nodules on her arms, legs, and breasts. Infection was found to be due to Mycobacterium abscessus. She was successfully treated with azithromycin, clofazimine, rifabutin, amikacin, imipenem-cilastatin-relebactam (Recarbrio™) and imipenem-cilastatin. This is the first described case of a M. abscessus infection successfully treated using this combination.

Inducible Resistance to Amikacin in Mycobacterium abscessus Isolated in Beijing, China

We aimed to determine the prevalence of amikacin (AMK) resistance of clinical Mycobacterium abscessus (MAB) isolates and to investigate if AMK resistance was induced by AMK exposure. A total of 75 MAB isolates underwent susceptibility testing for AMK after 3 and 14 days of incubation, respectively. The partial fragment of the rrs gene conferring AMK resistance was sequenced. The MIC values for AMK ranged from 0.5 to 128 μg/mL, with MIC50 and MIC90 values of 2 and 32 μg/mL, respectively. In addition, 9.3% of isolates (7/75) were resistant to AMK, all of which harbored a mutation within the rrs locus, including six with A1408G mutation and one with a C1409T mutation. Of note, the MICs of three isolates were significantly increased from 2 μg/mL to 64 μg/mL (one isolate) and 2 μg/mL to 128 μg/mL (two isolates), suggesting that three of the MAB isolates had inducible resistance to AMK. In conclusion, our data demonstrate that approximately one-tenth of clinical MAB isolates in Beijing harbored AMK resistance due to the acquisition of rrs mutations. Additionally, we firstly identified that intrinsic AMK resistance is inducible in MAB isolates, highlighting the urgent need to establish a proper method for the in vitro detection of AMK susceptibility in MAB.

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.

Association between 16S rRNA gene mutations and susceptibility to amikacin in Mycobacterium avium Complex and Mycobacterium abscessus clinical isolates

We evaluated the association between 16S rRNA gene (rrs) mutations and susceptibility in clinical isolates of amikacin-resistant nontuberculous mycobacteria (NTM) in NTM-pulmonary disease (PD) patients. Susceptibility was retested for 134 amikacin-resistant isolates (minimum inhibitory concentration [MIC] ≥ 64 µg/ml) from 86 patients. Amikacin resistance was reconfirmed in 102 NTM isolates from 62 patients with either Mycobacterium avium complex-PD (MAC-PD) (n = 54) or M. abscessus-PD (n = 8). MICs and rrs mutations were evaluated for 318 single colonies from these isolates. For the 54 MAC-PD patients, rrs mutations were present in 34 isolates (63%), comprising all 31 isolates with amikacin MICs ≥ 128 µg/ml, but only three of 23 isolates with an MIC = 64 µg/ml. For the eight M. abscessus-PD patients, all amikacin-resistant (MIC ≥ 64 µg/ml) isolates had rrs mutations. In amikacin-resistant isolates, the A1408G mutation (n = 29) was most common. Two novel mutations, C1496T and T1498A, were also identified. The culture conversion rate did not differ by amikacin MIC. Overall, all high-level and 13% (3/23) of low-level amikacin-resistant MAC isolates had rrs mutations whereas mutations were present in all amikacin-resistant M. abscessus isolates. These findings are valuable for managing MAC- and M. abscessus-PD and suggest the importance of phenotypic and genotypic susceptibility testing.

Etamycin as a Novel Mycobacterium abscessus Inhibitor

The increase in drug-resistant Mycobacterium abscessus, which has become resistant to existing standard-of-care agents, is a major concern, and new antibacterial agents are strongly needed. In this study, we introduced etamycin that showed an excellent activity against M. abscessus. We found that etamycin significantly inhibited the growth of M. abscessus wild-type strain, three subspecies, and clinical isolates in vitro and inhibited the growth of M. abscessus that resides in macrophages without cytotoxicity. Furthermore, the in vivo efficacy of etamycin in the zebrafish (Danio rerio) infection model was greater than that of clarithromycin, which is recommended as the core agent for treating M. abscessus infections. Thus, we concluded that etamycin is a potential anti-M. abscessus candidate for further development as a clinical drug candidate.