Emergence of Phytobacter diazotrophicus carrying an IncA/C2 plasmid harboring blaNDM-1 in Tokyo, Japan

Phytobacter diazotrophicus is an Enterobacterales species that was originally identifiedas a plant growth-promoting, Gram-negative bacterium. Recently, this species has been recognized as relevant to opportunistic human and nosocomial infections in clinical settings. Its frequent misidentificationas other Enterobacterales species from clinical examination occasionally causes a delay in the identificationof nosocomial outbreaks. Here, we report the emergence of New Delhi metallo-β-lactamase (NDM)-producing P. diazotrophicus isolated from hospitalized pediatric patients and hospital environments in Tokyo, Japan. In our case, these isolates were found during an investigation of carbapenem-resistant Enterobacterales in relation to nosocomial infections. Whole-genome sequencing is useful for overcoming the difficultyof species identification.Furthermore, we found that blaNDM-1 was carried by an IncA/C2 plasmid (approximately 170 kbp), which was transferrable from the clinical isolates to the recipient strain Escherichia coli J53. Our study demonstrated that P. diazotrophicus behaves as a carrier of blaNDM-harboring plasmids, potentially disseminating resistance to carbapenems among Enterobacterales.