Genetic mutations in linezolid-resistant Mycobacterium avium complex and Mycobacterium abscessus clinical isolates

Drugs for treating infections caused by non-tubercular mycobacteria: a narrative review from the study group on mycobacteria of the Italian Society of Infectious Diseases and Tropical Medicine

BACKGROUND

Non-tuberculous mycobacteria (NTM) are generally free-living organism, widely distributed in the environment, with sporadic potential to infect. In recent years, there has been a significant increase in the global incidence of NTM-related disease, spanning across all continents and an increased mortality after the diagnosis has been reported. The decisions on whether to treat or not and which drugs to use are complex and require a multidisciplinary approach as well as patients' involvement in the decision process.

METHODS AND RESULTS

This review aims at describing the drugs used for treating NTM-associated diseases emphasizing the efficacy, tolerability, optimization strategies as well as possible drugs that might be used in case of intolerance or resistance. We also reviewed data on newer compounds highlighting the lack of randomised clinical trials for many drugs but also encouraging preliminary data for others. We also focused on non-pharmacological interventions that need to be adopted during care of individuals with NTM-associated diseases CONCLUSIONS: Despite insufficient efficacy and poor tolerability this review emphasizes the improvement in patients' care and the needs for future studies in the field of anti-NTM treatments.

Phenotypic drug-susceptibility profiles and genetic analysis based on whole-genome sequencing of Mycobacterium avium complex isolates in Thailand

Mycobacterium avium complex (MAC) infections are a significant clinical challenge. Determining drug-susceptibility profiles and the genetic basis of drug resistance is crucial for guiding effective treatment strategies. This study aimed to determine the drug-susceptibility profiles of MAC clinical isolates and to investigate the genetic basis conferring drug resistance using whole-genome sequencing (WGS) analysis. Drug-susceptibility profiles based on minimum inhibitory concentration (MIC) assays were determined for 38 MAC clinical isolates (12 Mycobacterium avium and 26 Mycobacterium intracellulare). Mutations associated with drug resistance were identified through genome analysis of these isolates, and their phylogenetic relationships were also examined. Drug resistance, based on MIC values, was most commonly observed for moxifloxacin (81.6%), followed by linezolid (78.9%), clarithromycin (44.7%) and amikacin (36.8%). We identified specific mutations associated with resistance to amikacin. These include the rrs mutation at C464T in amikacin intermediate-resistance M. avium, and two mutations at T250A and G1453T in amikacin non-susceptible M. intracellulare. Mutations in rrl at A2058G, A2059C and A2059G were potentially linked to clarithromycin resistance. MAC clinical isolates not susceptible to linezolid exhibited mutations in rplC at G237C and C459T, as well as two rplD mutations at G443A and A489G. GyrB substitution Thr521Ala (T521A) was identified in moxifloxacin non-susceptible isolates, which may contribute to this resistance. A phylogeny of our MAC isolates revealed high levels of genetic diversity. Our findings suggest that the standard treatment regimen for MAC infections using moxifloxacin, linezolid, clarithromycin and amikacin may be driving development of resistance, potentially due to specific mutations. The combination of phenotypic and genotypic susceptibility testing can be valuable in guiding the clinical use of drugs for the treatment of MAC 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.

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.

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

BACKGROUND

The natural resistance of rapidly growing mycobacteria (RGM) to multiple antibiotics renders the treatment of the infections caused less successful. The objective of this study was to evaluate the in vitro susceptibilities of four oxazolidinones against different RGM species.

METHODS

The microplate alamarBlue assay was performed to identify the minimum inhibitory concentrations (MICs) of four oxazolidinones - delpazolid, sutezolid, tedizolid, and linezolid - for 32 reference strains and 115 clinical strains of different RGM species. The MIC breakpoint concentration was defined as 16 μg/ml for linezolid. Next, the gene fragments associated with oxazolidinone resistance were amplified and sequenced, and mutations were defined in contrast with the sequences of the reference strains.

RESULTS

Tedizolid showed the strongest inhibitory activity against the Mycobacterium abscessus isolates. Delpazolid exhibited better antimicrobial activity against the Mycobacterium fortuitum isolates when compared to linezolid, with 4-fold lower MIC values. The protein alignment and structure-based analysis showed that there might be no correlation between oxazolidinone resistance and mutations in the rplC, rplD, and 23S rRNA genes in the tested RGM.

CONCLUSIONS

Tedizolid had the strongest inhibitory activity against M. abscessus in vitro, while delpazolid presented the best inhibitory activity against M. fortuitum. This provides important insights into the potential clinical application of oxazolidinones to treat RGM infections.

Mycobacterium abscessus Associated Peritonitis with CAPD Successfully Treated Using a Linezolid and Tedizolid Containing Regimen Suggested Immunomodulatory Effects

Patient: Female, 38-year-old

Final Diagnosis: Peritonitis

Symptoms: Abdominal and/or epigastric pain

Medication:—

Clinical Procedure: —

Specialty: Infectious Diseases