Extraintestinal traits of pathogenicity and sequence type lineages in commensal Escherichia coli from adults and young children:We cannot draw a clear line between commensals and extraintestinal pathogens. Genotypic and phenotypic profiles of commensal Escherichia coli from adults and young children from Poland

Ewa Bok¹Justyna Mazurek-Popczyk¹Magdalena Wojciech²Katarzyna Baldy-Chudzik^1*

• ¹Department of Microbiology and Molecular Biology, Institute of Health Sciences, University of Zielona Góra, Zielona Góra, Poland
• ²Department of Applied Mathematics, Institute of Mathematics, University of Zielona Góra, Zielona Góra, Poland

Background: The commensal Escherichia coli population could play a crucial role in the pathogenesis of extraintestinal infections. The assignment to specific sequence type (ST) lineages and presence of particular combinations of virulence genes is a characteristic feature of extraintestinal pathogenic E. coli (ExPEC), but not exclusively. Extraintestinal virulence genes are also identified among commensal E. coli. The objective of this study was a genotypic and phenotypic characteristicscomparison of the extraintestinal virulence potential of two populations of commensal E.coli isolates from adults and young children.Methods: Genotypic traits were detected using PCR. Appropriate phenotypic assays and realtime PCR were used to analyze virulence factors expression. Multilocus sequence typing was performed using the seven-loci Achtman scheme.Genotypic studies revealed the virulence potential of the commensal isolates, and phenotypic analyses enabled to confirm if the genes are expressed. E.coli from adults carried pathogenicity islands and virulence genes in significantly higher proportions, resulting from the dominance of phylogroup B2 in this set of isolates. The hemolytic activity and higher levels of siderophore receptors expression were more common in E.coli from adults and were closely related to the dominance of phylogroup B2. Other traits not associated with phylogroup B2, such as adhesion abilities mediated by type 1 and P fimbriae and strong biofilm formation propensities, were detected with similar frequencies in both pools of isolates from adults and young children. E.coli harboring pathogenicity islands were subjected to multilocus sequence typing analysis. Sequence types ST73, ST59, ST131, ST95, ST141, and ST69 were most common in isolates from adults, whereas among E. coli from children: ST10, ST155, ST59, and ST1823. In our collection of E.coli, the isolates belonging to ST73 exhibited the highest potential for extraintestinal virulence.A significant proportion of E.coli from adults compared to young children exhibited considerable virulence potential, which may enable them to function as endogenous pathogens. Our research has highlighted the significant accumulation of extraintestinal pathogenicity features in commensal E. coli, indicating the need to monitor genetic and phenotypic profiles in "silent" potential pathogens. similarities in phylogeny and virulence potential between commensals and ExPEC strains, making it difficult to draw a clear boundary between them.