Cefiderocol-resistant pathogens in German hospital wastewater: a reservoir for multidrug resistance

Abstract

Cefiderocol-resistant bacteria pose a growing concern in both clinical and environmental settings. This study investigates cefiderocol-resistant bacteria in wastewater from six German tertiary care hospitals. A total of 36 samples were analysed using a culture-dependent approach involving cefiderocol pre-enrichment, yielding 97 cefiderocol-resistant isolates-primarily Enterobacter roggenkampii, Klebsiella oxytoca, Serratia marcescens, and Citrobacter farmeri. Most isolates exhibited high minimum inhibitory concentrations against cefiderocol and resistance to multiple antibiotics. Resistance rates were lower for meropenem-vaborbactam (10.3%) and imipenem-relebactam (33.0%), while all isolates remained susceptible to aztreonam-avibactam. Whole-genome sequencing of 79 isolates revealed a diverse resistome, with 78.5% (62/79) carrying carbapenemase genes. Some isolates harbored up to six distinct β-lactamase genes, including combinations of extended-spectrum β-lactamases (ESBLs), AmpC β-lactamases, and one or multiple carbapenemases-such as as bla_OXA-48 co-occurring with bla_NDM-1 or bla_VIM-1. In addition, biocide and heavy metal resistance genes were prevalent, highlighting bacterial adaptation to harsh environments. Plasmid profiling showed significant interspecies variation, with C. farmeri and K. oxytoca displaying the highest plasmid loads. Across all isolates, 38 unique plasmid incompatibility types were detected, 18 of which were species-specific. These findings highlight the multidrug-resistant nature of wastewater-derived pathogens and the importance of monitoring resistance dissemination in healthcare environments.

Keywords: Carbapenemases; Cefiderocol resistance; Multidrug-resistant pathogens; Pandrug-resistant bacteria; Plasmid incompatibility types; Wastewater surveillance.

Fig. 1

Phenotypic antimicrobial resistance detected in cefiderocol-resistant isolates of Citrobacter farmeri (n = 10), Enterobacter cloacae complex^a (n = 48), Klebsiella oxytoca complex^b (n = 24), and Serratia marcescens (n = 12). Abbreviations: FDC (cefiderocol), IMI (imipenem), I/R (imipenem-relebactam), MEM (meropenem), M/V (meropenem-voborbactam), CTX (cefotaxime), CAZ (ceftazidime), CZA (ceftazidime-avibactam), C/T (ceftolozane-tazobactam), PIP (piperacillin), TZP (piperacillin-tazobactam), AZA (aztreonam-avibactam), CHL (chloramphenicol), CIP (ciprofloxacin), LVX (levofloxacin), CST (colistin), SXT (sulfamethoxazole-trimethoprim), AMK (amikacin). (a) consisting of E. roggenkampii (n = 44), Enterobacter asburiae (n = 3), and Enterobacter soli (n = 1). (b) consisting of K. oxytoca (n = 16) and Klebsiella michiganensis (n = 8).

Fig. 2

Minimum-spanning tree of Enterobacter roggenkampii (n = 38) based on cgMLST analysis (2,466 loci). Each circle represents an individual isolate; numbers on connecting lines indicate allelic differences. Red-filled circles denote isolates belonging to ST165, while green-filled circles represent isolates assigned to a novel sequence type.

Fig. 3

Minimum-spanning tree of Klebsiella oxytoca (n = 11) isolates from TCH5 based on cgMLST (2,538 loci). Each circle represents an individual isolate; numbers on connecting lines indicate allelic differences. Red-filled circles indicate isolates belonging to ST2, while unfilled (colorless) circles represent isolates assigned to a novel sequence type.

Fig. 4

Minimum-spanning tree of Serratia marcescens (n = 12) based on cgMLST (2,682 loci). Each circle represents an individual isolate; numbers on connecting lines indicate allelic differences. Red-filled circles indicate isolates belonging to ST473, green-filled circles represent ST731, and unfilled (colorless) circles correspond to isolates assigned to novel sequence types.