Proteus mirabilis (P. mirabilis) is an opportunistic pathogen involved in urinary tract infections as well as various nosocomial infections. Emerging resistances to beta-lactams in this species complicates potential treatment since it is intrinsically resistant to colistin. Eleven isolates of carbapenem-non-susceptible P. mirabilis were identified in Sousse Hospital, Tunisia, from January 2018 to December 2022. MICs were determined and isolates were sequenced to determine their resistomes, sequence types, virulence factors, and their clonal relationships. Susceptibility testing showed that all isolates were resistant to carbapenems, aminoglycosides, fluoroquinolones, chloramphenicol, and the trimethoprim/sulfamethoxazole combination. They remained susceptible to the aztreonam/avibactam combination. All isolates produced NDM-1 carbapenemase and ArmA 16S rRNA methylase. In addition, one isolate co-produced the bla_VEB-6 gene. All isolates belonged to ST135, and phylogenetic analysis revealed that they were closely related. This study described the first outbreak of NDM-1-producing P. mirabilis in Tunisia.

Our study aims at characterizing a mcr-1-producing Escherichia coli ST224 clinical isolate collected at the University Hospital of Sahloul-Sousse from a joint infection. Phenotypic characterization was performed using a Vitek-2 System. NGS was performed by short-read (150 bp paired-end reads) sequencing on a NovaSeq6000 platform, as well as by long-read sequencing using an ONT R10.4 flow cell. Hybrid assembly was achieved using the Flye de novo assembler, and analyses were performed using tools of the Center for Genomic Epidemiology. The mcr-1-carrying plasmid was compared by BLAST to similar plasmids recovered in the NCBI database and visualized by PROKSEE. The collected E. coli belonged to ST224 and was multi-drug resistant, remaining susceptible to carbapenems, amikacin, gentamicin, and sulfamethoxazole only. Resistances to last-generation cephalosporins (mediated by bla_CMY-2) and fluoroquinolones were chromosomally-encoded. The mcr-1.1 gene was carried by an Inc12 plasmid similar but not identical to published data, and that lacked the two copies of the ISApl1 element usually bracketing the mcr-1.1 and pap2 genes. The dissemination of plasmid-encoded mcr-1 genes that can spread across species and sectors is a major health issue in countries such as Tunisia, where colistin is essential for the treatment of complicated human infections due to carbapenem-resistant Enterobacterales. Reporting all mcr-1-positive E. coli clinical isolates is thus important to understand the dynamic of spread of these resistant pathogens.

We report an OXA-204-producing Pseudomonas guariconensis clinical isolate in Tunisia, proving the spread of OXA-48 variants beyond Enterobacterales. The bla_OXA-204 gene was carried on a 119-kb chromosomally integrated plasmid fragment, along with multiple additional resistance genes. Surveillance, diagnostic tools, and antimicrobial drug access are needed to mitigate spread of carbapenem-resistant pathogens.

Background/Objectives: The emergence of plasmid-mediated mcr genes has enabled horizontal dissemination of resistance to colistin, a last-resort antibiotic against multidrug-resistant Enterobacterales. In Tunisia, genomic data on mcr-positive Escherichia coli are still limited. This study reports the genomic characterization of human clinical mcr-positive E. coli isolates from the Military Hospital of Tunis. Methods: Between August 2023 and March 2025, seven E. coli isolates with low-level colistin-resistance (MIC = 4–8 µg/mL) were collected from six patients. They were characterized by antibiotic susceptibility testing and WGS to determine resistome, MLST, genetic relatedness, and plasmid content. Results: The E. coli isolates belonged to diverse sequence types (STs), except for two isolates collected from the same patient 2.5 months apart, which were highly related. Overall, this pattern is consistent with a polyclonal spread. The mcr-1.1 gene was located on IncI2 (n = 5) or IncX4 (n = 2) plasmids, which exhibited high similarity both among themselves and in comparison with plasmids previously reported in human and livestock isolates. Most isolates were multidrug-resistant, harboring acquired resistance genes to multiple antibiotic classes, and chromosomal mutations conferring fluoroquinolone resistance. Three isolates additionally carried chromosomal insertions of the bla_CTX-M-55 gene. Resistance to cefiderocol was observed in one isolate and was associated with CirA and Fiu truncation. Conclusions: These findings highlight ongoing dissemination of mcr-1.1-positive E. coli isolates in Tunisia, primarily driven by plasmid transfer. Continuous genomic surveillance and One Health-oriented antibiotic stewardship are essential to limit the spread of colistin-resistance and the emergence of resistance to newer agents such as cefiderocol.