Mutation of TonB-Dependent Receptor Encoding Gene MCR_0492 Potentially Associates with Macrolides Resistance in Moraxella catarrhalis Isolates

Introduction

Moraxella catarrhalis, which is an opportunistic pathogen and is one of the three major pathogens of community-acquired pneumonia, causes a variety of infections in clinic. In recent years, the isolation rate of Moraxella catarrhalis has gradually increased. In China, due to the clinical empirical use of antibiotics, the resistance rate of Moraxella catarrhalis isolated from children to β-lactam antibiotics has reached 99%. The non-susceptible rate of Moraxella catarrhalis to macrolide antibiotics has also increased significantly.

Methods

Two isolates of Moraxella catarrhalis (R17123922_R and R18013231_R) were isolated from in-patients and were confirmed to be resistant to macrolide antibiotics using the standard disk diffusion and broth microdilution method recommended by CLSI. Whole-genome sequencing (WGS) analysis was performed in these two resistant strains.

Results

A total of 696 SNVs (single nucleotide variations), and 79 indels (Insertion and Deletion) were found in R17123922_R and R18013231_R. These SNVs and indels were distributed evenly in the genome, and no centralized distribution occurred. Moreover, two isolates did not harbor any previously reported mutations in the 23S rRNA and ribosomal proteins.

Conclusion

A novel indel in the MCR_0492 gene encoding TonB-dependent receptor protein was identified, and we speculated that TonB-dependent protein receptor may play an important role in macrolide resistance of Moraxella catarrhalis.

Antimicrobial Resistance and Respiratory Infections

Since their introduction into health care and clinical practice in the early 20th century, antibiotics have revolutionized medicine. Alarmingly, these drugs are increasingly threatened by bacteria that have developed a broad diversity of resistance mechanisms. Antibiotic resistance can be transferred between bacteria, often on mobile genetic elements; be acquired from the environment; or arise through mutation because of selective pressures of the drugs themselves. There are various strategies to resistance, including active efflux of the drug from the bacterial cell, reduced permeability of the cell envelope, alteration of the drug's target within the bacterial cell, and modification or destruction of the antibiotic. Streptococcus pneumoniae, Haemophilus influenzae, Pseudomonas aeruginosa, and Mycobacterium tuberculosis frequently are implicated in respiratory infections, often manifesting with reduced susceptibility to multiple classes of antibiotics. Some mechanisms of resistance, such as the β-lactamases that confer resistance to penicillins and related drugs, have been well characterized and are widespread in clinical isolates. Other newly identified determinants, including the colistin resistance gene mcr-1, are spreading rapidly worldwide and threaten last-resort treatments of multidrug-resistant organisms. Various approaches to detecting antibiotic resistance provide surveys of the determinants that are available for transfer into pathogenic bacteria. Together with molecular characterization of newly identified mechanisms, this surveillance can target drug discovery efforts and increase antibiotic stewardship. A greater understanding of the mechanisms of antibiotic resistance in respiratory pathogens combined with rapid diagnostics ultimately will reduce treatment failure due to inappropriate antibiotic use and prevent further spread of resistance.