Characterization of the First Carbapenem-Resistant Pseudocitrobacter faecalis Harboring bla(OXA-181) in China

With the wide use of carbapenems, carbapenem-resistant Enterobacterales have been increasingly reported worldwide. In this study, one bla(OXA-181)-positive Pseudocitrobacter faecalis strain was isolated from the blood culture of a patient with a bloodstream infection in China, which was its first clinical report outside Pakistan. Species identification of P. faecalis was initially performed using MALDI-TOF/MS and further confirmed by 16S rRNA gene and housekeeping gene sequencing. The antimicrobial susceptibility testing was determined through the broth microdilution method, and their clonal relationship was analyzed by pulsed-field gel electrophoresis. To study the transmission and genetic structure of the bla(OXA-181) gene, a transformation test and whole-genome sequencing (WGS) were performed. The results of the antimicrobial susceptibility testing indicated this P. faecalis was resistant to carbapenems, quinolones, and commonly used β-lactam/β-lactamase inhibitor combinations. Through WGS and transformation experiments, bla(OXA-181) and qnrS1 genes causing antibiotic resistance were located on a 55,148-bp length IncX3 type plasmid with a truncated ColKp3 replicon gene. As a rare species of Enterobacterales, P. faecalis was clinically reported in China for the first time, and the bla(OXA-181) gene it carried was located on a globally disseminated IncX3 plasmid. The spread of such bacteria and antibiotic resistance requires more clinical attention.