Molecular epidemiology and mechanisms of carbapenem and colistin resistance in Klebsiella and other Enterobacterales from treated wastewater in Croatia

This study isolated carbapenem-resistant Enterobacterales (CRE) from treated wastewater from a Zagreb wastewater treatment plant. The majority of CRE were Klebsiella spp., followed by Citrobacter spp. and Enterobacter cloacae complex. 18 different sequence types were identified, with 14 associated with human-associated clones. The most frequent carbapenemase genes in K. pneumoniae were blaOXA-48 and blaNDM-1. Colistin resistance was observed in 40% of Klebsiella and 57% of Enterobacter isolates. WGS analysis revealed various virulence genes and resistance genes to other antibiotics. The study highlights the significant role treated wastewater plays in harboring and spreading enterobacterial pathogens resistant to last-resort antibiotics.