Characterization of Diarreaghenic Escherichia coli Strains Isolated from Healthy Donors, including a Triple Hybrid Strain

Abstract

Escherichia coli is a well-recognized inhabitant of the animal and human gut. Its presence represents an essential component of the microbiome. There are six pathogenic variants of E. coli associated with diarrheal processes, known as pathotypes. These harbor genetic determinants that allow them to be classified as such. In this work, we report the presence of diarrheagenic pathotypes of E. coli strains isolated from healthy donors. Ninety E. coli strains were analyzed, of which forty-six (51%) harbored virulence markers specifics for diarrheagenic pathotypes, including four hybrids (one of them with genetic determinants of three DEC pathotypes). We also identified phylogenetic groups with a higher prevalence of B2 (45.6%) and A (17.8%). In addition, resistance to sulfonamides (100%), and aminoglycosides (100%) was found in 100% of the strains, with a lower prevalence of resistance to cefotaxime (13.3%), ceftriaxone (12.2%), fosfomycin (10%), and meropenem (0%). All analyzed strains were classified as multidrug resistant. Virulence genes were also investigated, which led us to propose three new virotypes. Among the virulence traits observed, the ability to form biofilms stands out, which was superior to that of the E. coli and Staphylococcus aureus strains used as positive controls.

Keywords: Escherichia coli; antimicrobial resistance; healthy donors; pathotypes.

Figure 1

Adherence patterns identified in this study. (A), localized adherence (present in strains Ec-9.3, Ec-37.1, Ec-41.3, Ec-44.2, Ec-36.1, Ec-36.3, Ec-31.3, and Ec-37.4); (B), aggregative adherence (observed in strains Ec-44.5, Ec-45.3, Ec-46.2, Ec-50.1, and Ec-50.2); (C), diffuse adherence (present in strains Ec-36.1 and Ec-36.3).

Figure 2

Biofilm formation assay. The dotted line represents 50% of the measurement parameter (1 g of total protein). The average of three assays was interpolated to a bovine serum albumin calibration curve. Red arrows indicate the four strains that showed a higher biofilm production, higher than 800 mg/g of total protein. S. aureus ATCC25923 (red bar) and E. coli ATCC25922 (blue bar) were used as positive controls.