Culture-based detection of clinically relevant carbapenemase genes in Gram-negative bacteria from aquatic environments in western Algeria.

Antimicrobial resistance (AMR) requires environmental surveillance because aquatic systems can receive resistant bacteria, antimicrobial residues and mobile resistance genes from domestic, agricultural, hospital and industrial sources. This culture-based study investigated culturable Gram-negative bacteria recovered from 12 inland, saline, wetland and coastal aquatic sites in western Algeria between January and April 2023. Bacterial isolates were identified by conventional biochemical methods and 16 S rRNA gene sequencing. Antimicrobial susceptibility was assessed by disk diffusion and selected broth microdilution assays, with colistin interpreted only by minimum inhibitory concentration. Phenotypic screening for extended-spectrum beta-lactamase-like and carbapenemase-associated activity was followed by targeted PCR and Sanger sequencing in selected high-risk isolates. Fifty-four Gram-negative isolates were recovered, including 44 fermenting and 10 non-fermenting isolates. Ten isolates, all fermenting Gram-negative bacteria, fulfilled the multidrug-resistant definition after exclusion of species-related intrinsic resistance. Targeted sequencing confirmed blaOXA-48 in two Escherichia coli isolates and one Cronobacter sakazakii isolate. One Escherichia coli isolate co-harbored blaNDM-1 and blaOXA-48. The colistin-resistant Pseudomonas aeruginosa isolate was negative for mcr-1. These findings provide baseline evidence that selected aquatic environments in western Algeria harbor culturable Gram-negative bacteria carrying clinically important carbapenemase genes. The study should be interpreted as targeted culture-based surveillance rather than a quantitative assessment of the aquatic resistome. These data represent the environmental component of AMR surveillance within a One Health framework and do not establish an epidemiological linkage to human or animal reservoirs.