Shigella bacteria isolated from fecal samples of men who have sex with men in Madrid have been found to carry extended-spectrum beta-lactamase genes alongside a broad array of additional resistance determinants and virulence factors, according to a genomic and phenotypic characterization study published in the journal Gut Pathogens. The research, conducted on isolates collected between 2017 and 2024, analyzed 30 Shigella flexneri and Shigella sonnei strains, including those producing ESBL enzymes and non-ESBL-producing controls, using antimicrobial susceptibility testing and whole-genome sequencing.
The study set out to characterize the phenotypic and genomic features of these isolates in detail. ESBL production was primarily associated with the blaCTX-M-27 gene, although blaCTX-M-15 was also detected, predominantly in isolates from MSM individuals. All ESBL genes were located on IncFII plasmids, with the exception of one S. flexneri isolate in which the gene was carried on an IncB/O/K/Z plasmid. The researchers note that, to their knowledge, this is the first report of S. flexneri harboring CTX-M-15 in MSM populations and one of the few reports of S. sonnei with similar characteristics.
Resistance to additional antibiotic classes was mediated by multiple acquired genes and by chromosomal mutations in the gyrA and parC genes. The study reports that resistance to additional antibiotic classes was mediated by multiple acquired genes and chromosomal mutations in gyrA and parC, in the context of rising prevalence of multidrug-resistant Shigella lineages that the authors describe as a growing international concern.
Phylogenetic analysis of the sequenced genomes revealed distinct clades within each serogroup. S. sonnei exhibited greater genetic diversity than S. flexneri across the sampled isolates. Nevertheless, lineage 3 predominated among the S. sonnei isolates, particularly the genotypes 3.6.1.1 and 3.6.1.1.2.
Virulence profiling identified variability in both plasmid- and chromosome-encoded determinants among the isolates. Virulence profiling identified differences in the presence of the pINV plasmid among the isolates. This variability in plasmid- and chromosome-encoded virulence determinants, including differences in the presence of the pINV plasmid, is part of the virulence profiling reported by the authors.
The background to the study underscores why these findings matter for public health. Shigella species are major causative agents of diarrheal disease worldwide, and reports of antimicrobial resistance associated with global dissemination have been increasing, particularly among men who have sex with men. Antimicrobial resistance in commonly isolated Shigella represents a growing international concern, especially given the rising prevalence of multidrug-resistant lineages. The Madrid collection, spanning 2017 to 2024, comprises S. flexneri and S. sonnei isolates with ESBL-producing phenotypes as well as non-ESBL-producing controls.
The detection of blaCTX-M-15 in S. flexneri from MSM individuals is highlighted by the authors as a novel observation. All ESBL genes were located on IncFII plasmids, except in one S. flexneri isolate, in which the gene was carried on an IncB/O/K/Z plasmid.
The study’s conclusion emphasizes the co-occurrence of multidrug resistance, virulence factors, and mobile genetic elements within the same circulating lineages. The authors frame this combination as underscoring the adaptive potential and epidemiological success of the Shigella strains they characterized.
The work was published open access in Gut Pathogens on 30 October 2026, with the article shared early to provide faster access to peer-reviewed, accepted research. The version available carries a permanent DOI and is citable, though it remains subject to further edits before the final Version of Record replaces it. The research team included Esther Culebras, Cristina GarcÃa-Salguero, Iciar RodrÃguez-Avial, Rodrigo López-Baltanás, Mercedes MartÃnez-RodrÃguez, Agustina Macchi and Alberto Delgado-Iribarren, among others.
The authors note that antimicrobial resistance in commonly isolated Shigella represents a growing international concern, especially given the rising prevalence of multidrug-resistant lineages.
Subject of Research: Genomic and phenotypic characterization of ESBL-producing Shigella flexneri and Shigella sonnei isolates from men who have sex with men in Madrid.
Article Title: Antimicrobial resistance, virulence and genetic characterization of ESBL-producing Shigella spp isolated from fecal samples of men who have sex with men
Article References: Culebras, E., GarcÃa-Salguero, C., RodrÃguez-Avial, I., López-Baltanás, R., MartÃnez-RodrÃguez, M., Macchi, A., & Delgado-Iribarren, A. (2026). Antimicrobial resistance, virulence and genetic characterization of ESBL-producing Shigella spp isolated from fecal samples of men who have sex with men. Gut Pathogens. https://doi.org/10.1186/s13099-026-00892-8
Image Credits: AI Generated
DOI: 10.1186/s13099-026-00892-8
Keywords: Shigella, ESBL, antimicrobial resistance, men who have sex with men, whole-genome sequencing, IncFII plasmids, CTX-M-27, CTX-M-15, virulence factors, Madrid, Gut Pathogens, multidrug resistance
News Source: Juliet Wilcox. (October 30, 2026). ESBL-producing Shigella strains in MSM carry multidrug resistance and virulence genes. Scienmag.
