No abstract

Bacterial resistance to carbapenem, which is mainly due to the successful dissemination of carbapenemase-encoding genes, has become a major health problem. Few studies have aimed to characterize the level of resistance in the environment, notably in hospital wastewater, which is a likely hotspot for exchange of antibiotic resistance genes. In this work, we looked for the presence of imipenem-resistant bacteria and imipenem in the effluent of the teaching hospital of Clermont-Ferrand, France. Selective growth of bacteria from 14-day old biofilms formed in the pipe sewer showed that 22.1% of the isolates were imipenemresistant and identified as Aeromonas (n=23), Pseudomonas (n=10), Stenotrophomonas (n=4) and Acinetobacter (n=1). Fifteen of these strains harbored acquired carbapenemase-encoding genes bla VIM (n=11), bla OXA-48 (n=2), bla GES (n=1), bla NDM (n=1). All isolates also harbored associated resistances to aminoglycosides, fluoroquinolones and/or tetracyclin. S1-nuclease pulsed-field gel electrophoresis analysis of eight selected isolates showed that four of them harbored one to two plasmids of molecular weight between 48.5Kb and 194Kb. In vitro transformation assays evidenced the presence of bla VIM and bla NDM on plasmids with the bla VIM harboring 80 Kb plasmid having conjugative capacity. The predicted environmental concentration of imipenem in the hospital effluent was 3.16 µg/L, suggesting that biofilm bacteria are subjected to sub-MICs of imipenem within the effluent. However, no imipenem molecule was detected in the hospital effluent, probably owing to its instability: in vitro assays indicated that imipenem's biological activity was no longer detectable after 45h of storage. However, the predictive value of the hazard quotient relative to the development of resistance was greater than 1.0 (HQr=28.9 ± 1.9), which indicates a possible risk. The presence of carbapenemase-encoding genes in hospital effluent biofilm strains and their ability to transfer are therefore a potential hazard that should not be neglected and points to the need for monitoring antibiotic resistance in hospital wastewater.