Nodari, C. S. | bioRxiv Science

bioRxiv2026

Flex-It: A global standardised genotyping framework for Shigella flexneri

Shigella flexneri is the leading causative agent of shigellosis globally. The public health threat posed by S. flexneri is compounded by its emergence as a sexually transmissible infection, importance of international travel in driving dissemination, and the increasing prevalence of antimicrobial resistance (AMR). A rapid and robust computational method is needed to enhance genomic surveillance and systematically explore features of the population structure of this WHO priority pathogen, which is scalable and readily implementable across jurisdictions, particularly as vaccine development efforts are underway. Here, we present Flex-It, a genomic framework and genotyping scheme implemented in Mykrobe for S. flexneri serotypes 1-5, X & Y, compatible with previous approaches used to describe S. flexneris population structure. To develop Flex-It, we curated a retrospective dataset of 5,819 publicly available S. flexneri genomes. We characterised the global population structure for S. flexneri, exploring geographical and temporal traits, and showed the granular diversity of AMR and serotype profiles. We applied Flex-It to >13,000 genomes routinely generated by public health laboratories from Australia, the UK and the USA across a ten-year period. We found significant genotype diversity in all three locations, with the emergence of genotypes with converged resistance to all major drugs currently used for treatment. Flex-It provides an open-source, novel genotyping method that rapidly characterises S. flexneri and its ciprofloxacin resistance determinants in <1 minute from both short and long whole-genome sequencing reads. Flex-It provides the community with a standardised nomenclature to monitor the emergence and spread of S. flexneri lineages.

microbiology↗

bioRxiv2019

Virulence potential of a multidrug-resistant Escherichia coli belonging to the emerging clonal group ST101-B1 isolated from bloodstream infection

Escherichia coli EC121 is a multidrug-resistant (MDR) strain isolated from bloodstream infection of an inpatient with persistent gastroenteritis and Zone T lymphoma, that died due to septic shock. Despite causing an extraintestinal infection, it harbors few known virulence factors and was assigned into phylogenetic group B1. To evaluate if the EC121 was pathogenic or opportunistic, its genome was sequenced, and an in vitro characterization of some pathogenicity-associated properties was performed. The data retrieved from genome analysis showed that E. coli strain EC121 belongs to the O154:H25 serotype, and to ST101-B1, which was epidemiologically linked to extraintestinal infections and antimicrobial resistance spread as well. Moreover, it was closely related to Shiga-toxin producing E. coli (STEC). Besides, strain EC121 is an MDR strain harboring 14 antimicrobial resistance genes, including blaCTX-M-2, and more than 50 complete virulence genetic clusters, which are reported to be associated either with DEC or ExPEC. The strain also displays the capacity to adhere to a variety of cell lineages, and invade T24 bladder cells, as well as the ability to form biofilms on abiotic surfaces, and survive the bactericidal serum complement activity. Additionally, it is virulent in the Galleria mellonella model. Altogether, E. coli EC121 unveiled to be a pathogen powered by its multi-drug resistance characteristic. Carry out studies providing accurate information about the virulence potential of all kinds of MDR strains are essential because these studies will help in the development of alternative therapies of infection management and spread control of MDR strains. Authors summaryThe phylogenetic origin of extraintestinal pathogenic Escherichia coli is mostly associated with phylogroup B2, and the majority of the studies regarding extraintestinal infection focus on the most virulent strains, which might also present multidrug-resistant (MDR) phenotype. Strains belonging to phylogroup B1 and isolated from extraintestinal infections are considered as opportunist pathogens and have their virulence neglected. We focus our study in one MDR strain isolated from bloodstream infection that belongs to phylogenetic group B1 to enlarge the knowledge about the virulence of this kind of strain. We demonstrated that the EC121 is capable of adheres to intestinal and bladder human cells, and invades the latter one; it survives to human serum bactericidal effects and produces biofilm. Additionally, the in vivo assay confirmed the EC121 virulence, showing that it should be considered a pathogenic strain. The genetic analyzes highlighted important aspects of EC121 which are typical from strains of sequence type 101, like its involvement in the spread of antimicrobial resistance genes and its relationship with extraintestinal infection from diverse sources. Information concerning the virulence of MDR strains is important for the development of global actions treating the spread of antimicrobial resistance, as well as to elucidate the pathogenesis of strains that were considered as an opportunist.

microbiology↗