First detection of autochthonous extensively drug-resistant NDM-1 Pseudomonas aeruginosa ST235 from a patient with bloodstream infection in Italy, October 2019.

Background: Pseudomonas aeruginosa (PA) is one of the most common and serious causes of healthcare-associated bacteremia. The emergence and dissemination of multidrug-resistant (MDR) and extensively drug-resistant (XDR) PA strains pose a major clinical concern. ST235-PA is a high-risk clone which shows a high capacity to acquire antibiotic resistance. Here we describe the first autochthonous New Delhi metallo-β-lactamase (NDM)-producing Pseudomonas aeruginosa ST235 identified in Italy.

Case Presentation: In October 2019, a patient residing in an elderly health care and rehabilitation facility, was hospitalized and died from sepsis caused by an XDR-PA. The strain belonged to the high-risk clone sequence type ST235. Whole genome sequencing (WGS) revealed the presence of genes encoding NDM-1 and multiple β-lactamases, many clinically significant multidrug efflux pump complexes and also the virulence gene ExoU, which is associated with a high cytotoxic phenotype.

Conclusions: Few strains of NDM-1-PA have been identified worldwide, all belonging to ST235. The combination of ST235 and ExoU is a predictor of highly unfavorable prognosis. The potential spread of these high-risk clones in healthcare settings is worrisome because treatment options are limited. Early identification of high-risk clones could help in outbreaks investigation and infections control.