In both humans and animals, the spread of Extended-Spectrum -Lactamases (ESBL)/AmpC producers has become a major issue, particularly due to the plasmidic dissemination of most of these genes. Besides, over-expression of the chromosomal ampC gene was largely reported in human and animal Enterobacteriaceae and, more recently, modifications within the coding region of the ampC gene (encoding Extended-spectrum AmpC -lactamases (ESACs)) were shown to be responsible for an hydrolysis spectrum expanded to oxyiminocephalosporins in humans. In this study, among 6765 cattle E. coli isolates, 28 (0.37%) isolates harboring a reduced susceptibility to cefepime (MICs ranging from 0.5 to 12 g/ml) were investigated as presumptive ESACs producers. Highly conserved mutations in the promoter/attenuator region were identified at positions -88, -82, -42, -18, -1 and +58. Using sequencing and cloning experiments, amino acid substitutions of the AmpC beta-lactamase were characterized at positions 287 (mostly S287N, but also S287C), 292 (A292V) and 296 (H296P), similarly to data reported in humans. Interestingly, those cattle ESAC-producing E. coli isolates predominantly belonged to the Clonal Complex (CC)23, thus mirroring what has been described in humans. The driving forces for the selection of ESACs in animals are unknown, and their prevalence needs to be further investigated in the different animal sectors. Considering the over-representation of ESAC-producing E. coli belonging to CC23 in both humans and animals, exchanges of ESAC producers between the two populations may have occurred as well. To our best knowledge, this study is the first report of ESACs in animals worldwide, which should be considered an emerging mechanism contributing to the resistance to extended-spectrum cephalosporins in the animal population.

Molecular features of the first carbapenem-resistant Klebsiella pneumoniae isolates (KP1 and KP2) from the University Hospital Tahar Sfar, Tunisia, were investigated. Antimicrobial susceptibility testing, multilocus sequence typing, S1 nuclease pulsed-field gel electrophoresis, Southern blot, and polymerase chain reaction (PCR)-based replicon typing were performed. Extended-spectrum β-lactamases and carbapenemase genes were detected by PCR and sequencing. Both isolates were multidrug resistant. KP1 was of sequence type (ST) ST101 and exhibited bla _CTX-M-15 and bla _TEM-1 on an untypeable plasmid and bla _OXA-48 on an IncL/M plasmid. KP2 was genetically unrelated to KP1 (ST147) and harbored an IncA/C plasmid carrying bla _CMY-4 and the bla _OXA-48 derivative gene: bla _OXA-204 . This study reports the second case worldwide of an OXA-204-producing K. pneumoniae isolate from the same country, however, in a different genetic background.

Enterobacterales resistant to extended-spectrum cephalosporins (ESC) are a marker of the antimicrobial resistance (AMR) burden. They are infecting humans, but the intestinal microbiota can also be transiently colonized without developing symptoms. Healthy carriage can promote silent dissemination of resistant bacteria, and data on this colonization are often lacking. Between 2021 and 2023, a sampling of healthy Tunisian people was carried out. Fecal samples (n = 256) were plated on selective agar, and all collected isolates were characterized by phenotypic (antibiograms) and genomic (whole-genome sequencing) methods. A total of 26 (26/256, 10.2%) isolates were collected, including 24 Escherichia coli and 2 Klebsiella pneumoniae. In total, 17 isolates (15 E. coli and 2 K. pneumoniae) presented an ESBL phenotype conferred by the bla_CTX-M-15 gene, and 9 E. coli isolates presented an AmpC phenotype conferred by the bla_DHA-1 gene. K. pneumoniae belonged to ST1564 and ST313, while E. coli belonged to diverse STs including the pandemic ST131 clone. Clonally related ST349 E. coli isolates carrying the bla_DHA-1 gene were found in nine individuals. In parallel, four bla_CTX-M-15 -positive E. coli isolates carried this ESC-resistance gene on an epidemic plasmid IncF/F-:A-:B53 previously identified in Tunisian pigeons and fish. These findings highlight the spread of genetically diverse ESC-resistant Enterobacterales as well as an epidemic plasmid in Tunisia, emphasizing the need for antimicrobial stewardship to limit the transmission of these resistances in the Tunisian population.