Intestinal Carriage of Extended-Spectrum Cephalosporin-Resistant Enterobacterales in Farmed Sea Bream ( Sparus aurata ) Marketed in Algiers

This study investigated the intestinal carriage of extended-spectrum cephalosporin-resistant (ESC-R) Enterobacterales in farmed sea bream ( Sparus aurata ) marketed in Algiers. A total of 108 intestinal samples were collected from seven fishmongers between 2023 and 2024. ESC-R Enterobacterales were detected in 16.7% of the samples (18/108), including Klebsiella pneumoniae ( n = 9), Escherichia coli ( n = 8), and Klebsiella michiganensis ( n = 1). Whole-genome sequencing confirmed the presence of genes conferring an extended-spectrum β-lactamase phenotype in 17 isolates (mostly bla _CTX-M-15 ) and an AmpC cephalosporinase phenotype in one isolate. Moreover, the mcr-1.1 and fosA3 genes, which respectively confer resistance to colistin and fosfomycin, were detected in a single E. coli isolate. To the best of our knowledge, this is the first report of plasmid-mediated colistin resistance in Algerian aquaculture. Most isolates (72.2%) exhibited a multidrug-resistant (MDR) phenotype, mainly involving resistance to tetracyclines, sulfonamide-trimethoprim, and streptomycin. Several sequence types (STs) identified in this study, including the high-risk clones E. coli ST131 and K. pneumoniae ST37, have previously been reported in humans and animals. In addition, two ESC-R Aeromonas caviae isolates were recovered. These findings demonstrate the occurrence of ESC-resistant bacteria in the intestinal microbiota of farmed sea bream marketed in Algiers and underscore the need for integrated One Health surveillance to better understand the role of aquaculture in the emergence, maintenance, and dissemination of MDR bacteria and antimicrobial resistance determinants.