Virulence profiling and biofilm-forming capacity of different E. coli pathotypes and phylogroups isolated from calf diarrhoea

Different Escherichia coli (E. coli) pathotypes are known to cause recurring and widespread calf diarrhoea, leading to substantial economic losses in the livestock industry. This study aimed to evaluate the prevalence of E. coli in calves with diarrhoea and to describe the molecular characteristics of 100 obtained isolates. The isolates were tested for virulence genes, such as papC, eaeA, stI, stII, ltI, stx1, stx2, cnf1 and cnf2, and genes for phylogenetic classification (chuA, yjaA, arpA, TspE4.C2 DNA fragment, arpAgpE, and trpAgpC). Additionally, their biofilm-forming ability was evaluated. The study also examined and compared the effectiveness of two forms of zinc oxide (ZnO) - classical inorganic and nanoparticle - at five different concentrations against strong biofilm producers. The detected virulence gene frequencies were: papC (44%), stx2 (20%), cnf1 (16%), eaeA (13%), cnf2 (13%), stx1 (4%) and st1 (1%). The isolates were divided into seven phylogroups, with the most common being D (32%), followed by B1 (25%), B2 (12%), C (10%), E (10%), A (9%) and F (2%). About 87% of the isolates could form biofilms, with 32% classified as strong biofilm producers. Both forms of ZnO inhibited biofilm formation at all tested concentrations, with nanoparticles showing slightly better efficacy. These findings demonstrate that calves with diarrhoea harbour various E. coli pathotypes, including STEC, NTEC, EPEC, ETEC and EHEC, many of which can form biofilms.