**Antimicrobial Treatment on a Catheter-Related Bloodstream Infection (CRBSI) Case Due to Transition of a Multi-Drug-Resistant** *Ralstonia mannitolilytica* **from Commensal to Pathogen during Hospitalization**

**Junyan Liu 1,2,† , Brian M. Peters 3,†, Ling Yang 4,5,\*, Hui Yu <sup>4</sup> , Donghua Feng <sup>4</sup> , Dingqiang Chen 4,5 and Zhenbo Xu 6,7,\***


**Abstract:** Despite its commonly overlooked role as a commensal, *Ralstonia mannitolilytica* becomes an emerging global opportunistic human pathogen and a causative agent of various infections and diseases. In respiratory illnesses, including cystic fibrosis and chronic obstructive pulmonary disease (COPD), *R. mannitolilytica* is also identified presumably as colonizer. In this study, one distinctive clone of *R. mannitolilytica* was firstly identified as colonizer for the first 20 days during hospitalization of a patient. It was then identified as a causative agent for catheter-related bloodstream infection with negative identification after effective treatment, verifying its transition from commensal to pathogen. In conclusion, we provide convincing evidence that during hospitalization of a patient, *R. mannitolilytica* transitioned from commensal to pathogen in the respiratory tract leading to catheterrelated bloodstream infection (CRBSI).

**Keywords:** *Ralstonia mannitolilytica*; chronic obstructive pulmonary disease (COPD); catheter-related bloodstream infection (CRBSI); commensal; pathogen

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).
