Molecular Epidemiology of Carbapenem-Resistant Klebsiella aerogenes in Japan.

Information regarding Klebsiella aerogenes haboring carbapenemase in Japan is limited. A comprehensive nationwide survey was conducted from September 2014 to December 2022, and 67 non-duplicate strains of carbapenem-resistant K. aerogenes were isolated from 57 healthcare facilities in Japan. Through genetic testing and whole-genome sequencing, six strains were found to possess carbapenemases, including imipenemase (IMP)-1, IMP-6, New Delhi metallo-β-lactamase (NDM)-1, and NDM-5. The strain harboring bla NDM-5 was the novel strain ST709, which belongs to the clonal complex of the predominant ST4 in China. The novel integron containing bla IMP-1 featured the oxacillinase-101 gene, which is a previously unreported structure, with an IncN4 plasmid type. However, integrons found in the strains possessing bla IMP-6 , which were the most commonly identified, matched those reported domestically in Klebsiella pneumoniae , suggesting the prevalence of identical integrons. Transposons containing bla NDM are similar or identical to the transposon structure of K. aerogenes harboring bla NDM-5 previously reported in Japan, suggesting that the same type of transposon could have been transmitted to K. aerogenes in Japan. This investigation analyzed mobile genetic elements, such as integrons and transposons, to understand the spread of carbapenemases, highlighting the growing challenge of carbapenem-resistant Enterobacterales in Japan and underscoring the critical need for ongoing surveillance to control these pathogens.