# Phenotypic and genomic characterization of Roseomonas mucosa, an opportunistic pathogen with discrepancies among antimicrobial susceptibility testing methods

## TL;DR

This study examines antibiotic resistance patterns and genetic factors in Roseomonas mucosa, a bacterium that causes infections in immunocompromised patients.

## Contribution

The study identifies a novel regulatory mechanism of beta-lactamase expression in R. mucosa that explains discrepancies in susceptibility testing.

## Key findings

- High susceptibility to aminoglycosides, fluoroquinolones, and carbapenems was observed in R. mucosa strains.
- Discrepancies in susceptibility testing methods were linked to a class A beta-lactamase regulated by an LysR-type regulator.

## Abstract

Roseomonas mucosa is an opportunistic bacterium found in clinical and environmental samples that primarily affects immunocompromised patients. Treatment is challenging owing to the lack of standardized susceptibility testing methods, breakpoints, and variable antimicrobial resistance profiles published. This study evaluated different antimicrobial susceptibility testing approaches and searched for new insights into resistance mechanisms, especially against third-generation cephalosporins. Antimicrobial susceptibility profiles of a panel of 17 R. mucosa strains were analyzed using disk diffusion method (DDM), broth microdilution (BMD) method, and MIC gradient strips. Discrepancies between susceptibility methods were further explored using beta-lactamase inhibitors, whole-genome sequencing, and transcriptomic analyses. Antimicrobial susceptibility testing revealed high susceptibility to aminoglycosides, fluoroquinolones, and carbapenems, while resistance to many beta-lactams was detected. Significant discrepancies were observed between the DDM and BMD methods, particularly with respect to the use of third- and fourth-generation cephalosporins and aztreonam. Genomic analysis identified two putative class-A and one class-C beta-lactamases within all strains. Transcription of one class A beta-lactamase, controlled by an lysR regulator, was significantly induced by cephalosporins and explained the phenotype observed. This study provides the antimicrobial susceptibility profiles against a large panel of antibiotics from 17 R. mucosa strains. It also explained the deep discrepancies between phenotypic approaches regarding cephalosporins.