Antibiotic resistance, virulence, and phylogenetic analysis of Escherichia coli strains isolated from free-living birds in human habitats

Wild birds can be colonized by bacteria, which are often resistant to antibiotics and have various virulence profiles. The aim of this study was to analyze antibiotic resistance mechanisms and virulence profiles in relation to the phylogenetic group of E. coli strains that were isolated from the GI tract of wildfowl. Out of 241 faecal samples, presence of E. coli resistant to a cephalosporin (ESBL/AmpC) was estimated for 33 isolates (13,7%). Based on the analysis of the coexistence of 4 genes encoding ESBLs/AmpC (bla(CTX-M), bla(TEM,) bla(SHV), bla(AmpC)) and class 1 and 2 integrons genes (intI1, intI2) a subset of two resistance profiles was observed among the investigated E. coli isolates carrying bla(AmpC), bla(SHV), and bla(CTX-M), bla(TEM), class 1 and 2 integrons, respectively. The E. coli isolates were categorized into 4 phylogenetic groups A (39.4%), B2 (24.25%), D (24.25%) and B1 (12.1%). The pathogenic B2 and D groups were mainly typical for the Laridae family. Among the 28 virulence factors (Vfs) detected in pathogenic phylogenetic groups B2 and D, 7 were exclusively found in those groups (sfa, vat, tosA, tosB, hly, usp, cnf), while 4 VFs (fecA, fyuA, irp2, kspMTII) showed a statistically significant association (P≤0.05) with phylogroups A and B1. Our results indicated that strains belonging to commensal phylogroups A/B1 possess extensive iron acquisition systems (93,9%) and autotransporters (60,6%), typical for pathogens, hence we suggest that these strains evolve towards higher levels of virulence. This study, which is a point assessment of the virulence and drug resistance potential of wild birds, confirms the importance of taking wild birds as a reservoir of strains that pose a growing threat to humans. The E. coli analyzed in our study derive from different phylogenetic groups and possess an arsenal of antibiotic resistance genes and virulence factors that contribute to their ability to cause diseases.