FosA3 emerging in clinical carbapenemase-producing .

Fosfomycin (FOS) is an effective antibiotic against multidrug-resistant , but its effectiveness is reducing. Little is known on the current prevalence of FosA enzymes in low-risk pathogens, such as . The aim of the study was the molecular characterization of a carbapenemase- and FosA-producing collected in Italy. AK867, collected in 2023, showed an XDR profile, retaining susceptibility only to colistin. AK867 showed a FOS MIC >128 mg/L by ADM. Based on WGS, AK867 belonged to ST116 and owned a wide resistome, including , KPC-2, and VIM-1. was carried by a conjugative pKPC-CAV1312 plasmid of 320,480 bp, on a novel composite transposon (12,907 bp). FosA3 transposon shared similarities with other -harboring pKPC-CAV1312 plasmids among spp. We report the first case of FosA3 production in clinical carbapenemase-producing ST116. The incidence of FosA3 enzymes is increasing among , affecting even low-virulence pathogens, as .