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, strain EC121 harbors very few known virulence factors associated with extraintestinal pathogenic E. coli (ExPEC). Furthermore, this strain was assigned to phylogenetic group B1, which is usually related to commensals or diarrheagenic E. coli (DEC) strains, being rarely linked to extraintestinal infections. The question rises if E. coli EC121 is opportunistic or does have a true virulence potential. To address this question the genome of strain EC121 was sequenced, and an in vitro characterization of some pathogenic-associated properties was performed. The data retrieved from genome analyses showed that E. coli strain EC121 belongs to the O154:H25 serotype, and to the sequence type 101-B1 (ST101-B1), which has been epidemiologically linked to extraintestinal infections and antimicrobial resistance spread as well. Moreover, it is shown to be 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, or both. Strain EC121 also displays the capacity to adhere to and invade HeLa cells, intestinal Caco-2 cells and bladder T24 cells, as well as the ability to form biofilms on abiotic surfaces, and survive the bactericidal serum complement activity. Altogether, the genetic and phenotypic traits presented by E. coli EC121 may be unveiling a pathogen powered by its multi-drug resistance characteristic. The recognition of such MDR pathogens makes it essential to carry out studies providing accurate information about their virulence potential. Such studies will help in the development of alternative therapies of infection management and spread control of MDR strains. Author summary Extraintestinal pathogenic Escherichia coli are mostly associated with phylogenetic group B2 and the majority of the studies regarding extraintestinal infection focus on the most virulent strains, which might also possess multidrug-resistant phenotype, like the ST131 strains. On the other hand, strains that belong to phylogroup B1 and are isolated from extraintestinal infections are almost neglected, being considered as merely opportunist pathogens, and the majority of studies reporting strains from this phylogroup focus on antimicrobial resistance. We concentrated our research on one multidrug-resistant 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 strain EC121 has full potential to be considered a pathogenic strain, because it adheres to and invades intestinal and bladder human cells and survives in human serum; moreover, our data highlight some important EC121 features, which are typical of ST101 strains, like its involvement in the spread of antimicrobial resistance genes, its relationship with extraintestinal infections from diverse sources, and its close relatedness to Shiga toxin-producing E. coli. All these data are important for the development of global actions concerning the spread of antimicrobial resistance, as well as to elucidate the virulence potential of strains that at first glance may be considered as a mere opportunist.