Novel insights into genetic characteristics of bla_GES-encoding plasmids from hospital sewage

The prevalence of Guiana extended-spectrum (GES)-type carbapenemase producers is increasing worldwide, and hospital water environments are considered as potential reservoirs. However, the genetic features underlying this resistance are not yet fully understood. This study aimed to characterize bla_GES-encoding plasmids from a single-hospital sewage sample in Japan.

Carbapenemase producers were screened using carbapenemase-selective agar and polymerase chain reaction. Whole-genome sequencing analyzes were performed on the carbapenemase-producing isolates.

Eleven gram-negative bacteria (four Enterobacter spp., three Klebsiella spp., three Aeromonas spp., and one Serratia spp.) with bla_GES-24 (n = 6), bla_GES-6 (n = 4), and bla_GES-5 (n = 1) were isolated from the sewage sample. Five bla_GES-24 and a bla_GES-5 were localized in IncP-6 plasmids, whereas three bla_GES-6 plasmids were localized in IncC plasmids with IncF-like regions. The remaining bla_GES-6 and bla_GES-24 were, respectively, localized on IncFIB-containing plasmids with IncF-like regions and a plasmid with an IncW-like replication protein. The IncP-6 and IncW-like plasmids had a close genetic relationship with plasmids from Japan, whereas the IncC/IncF-like and IncFIB/IncF-like plasmids were closely related to those from the United States and Europe. All bla_GES genes were located on the class 1 integron cassette of the Tn3 transposon-related region, and the IncC/IncF-like plasmid carried two copies of the integron cassette. Eight of the eleven bla_GES-encoding plasmids contained toxin-antitoxin system genes.

The findings on the plasmids and the novel genetic content from a single wastewater sample extend our understanding regarding the diversity of resistance and the associated spread of bla_GES, suggesting their high adaptability to hospital effluents. These findings highlight the need for the continuous monitoring of environmental GES-type carbapenemase producers to control their dissemination.