Meropenem degradation does not necessarily eliminate antibacterial activity: responses of model and environmental bacterial isolates
Year: 2026
Type: preprint
Abstract: Carbapenems can degrade rapidly in aquatic systems, and disappearance of the parent compound is often interpreted as loss of antibacterial activity. Here, we compared the antibacterial effects of intact meropenem with those of a meropenem mixture incubated for eight days in the presence of biofilm-covered moving-bed biofilm reactor carriers. During incubation, parent meropenem became undetectable, while several transformation products (TPs) retaining a closed β-lactam ring, a key structural feature for antibacterial activity, formed and persisted through the incubation period. The intact antibiotic and the incubated meropenem mixture containing TPs were tested against Escherichia coli, Pseudomonas fluorescens and two environmental isolates, CIS1 and CIR3, using optical density and viable cell counts. While intact meropenem strongly reduced viable counts of E. coli, P. fluorescens and CIS1, CIR3 was able to grow in its presence. In contrast, the incubated meropenem TPs mixture exhibited lower toxicity overall. Little or no TP inhibition was detected for P. fluorescens and E. coli, while CIS1 showed a weaker and time-dependent response. CIR3 was not suppressed by the mixture. Although the observed responses were subtle, the results show that disappearance of parent meropenem does not necessarily coincide with complete loss of meropenem-derived biological effects. The findings highlight that meropenem TPs should be considered when evaluating the environmental relevance of meropenem degradation and its potential contribution to selective pressure of antibiotics.
Source: ChemRxiv
Language: English
Subfield: Pollution
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
Funders: Aarhus Universitet, Villum Fonden
OpenAlex ID: W7220952896