Occurrence and functionality of cycle inhibiting factor, cytotoxic necrotising factors and cytolethal distending toxins in Escherichia coli isolated from calves and dogs in Italy

Escherichia coli isolated from animals up to three months of age, with diarrhea (255 calves and 29 dogs (pups)), without diarrhea (21 calves and 11 pups, used as controls), and 58 adult dogs with cystitis were tested to investigate the occurrence and functional expression of cyclomodulins cycle inhibiting factor (CIF), cytotoxic necrotizing factors (CNFs) and cytolethal distending toxins (CDTs). In cyclomodulin-positive isolates the association was assessed with other virulence genotypes and phylogenetic groups. Of 374 E. coli isolates, 80 (21.4%) were positive for at least one cyclomodulin and 14 of the latter (3.7%) showed different combinations of more than one. cif-positive isolates showed a low number of additional virulence factors, and were commonly associated with phylogroup B1, while cnf- and cdt-positive isolates, harboring many extraintestinal virulence factors, belonged to phylogroups B2 and D. Almost all isolates showed an irreversible cytopathic effect (CPE), displaying functionality of cyclomodulins. Five isolates that presented a mutation of cif were CPE-negative.