Environmental spreading of clinically relevant carbapenem-resistant gram-negative bacilli: the occurrence of bla(KPC-or-NDM) strains relates to local hospital activities

BACKGROUND: Aquatic matrices impacted by sewage may shelter carbapenem-resistant (CR) Gram-negative bacilli (GNB) harboring resistance genes of public health concern. In this study, sewage treatment plants (STPs) servicing well-defined catchment areas were surveyed for the presence of CR-GNB bearing carbapenemase genes (bla(KPC) or bla(NDM)). RESULTS: A total of 325 CR-GNB were recovered from raw (RS) and treated (TS) sewage samples as well as from water body spots upstream (UW) and downstream (DW) from STPs. Klebsiella-Enterobacter (KE) group amounted to 116 isolates (35.7%). CR-KE isolates were recovered from TS, DW (35.7%) and RS samples (44.2%) (p = 0.001); but not from UW samples. KE isolates represented 65.8% of all bla(KPC) or bla(NDM) positive strains. The frequency of bla(KPC-or-NDM) strains was positively associated with the occurrence of district hospitals located near STPs, as well as with the number of hospitalizations and of sewer connections serviced by the STPs. bla(KPC-or-NDM) strains were recovered from ST samples in 7 out of 14 STPs, including four tertiary-level STPs; and from 6 out of 13 DW spots whose RS samples also had bla(KPC-or-NDM) strains. CONCLUSIONS: Clinically relevant GNB bearing bla(KPC-or-NDM) resist sewage treatments and spread into environmental aquatic matrices mainly from STPs impacted by hospital activities. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12866-021-02400-1.