Neonatal sepsis is a disease affecting newborns ≤1 month of age with clinical symptoms and positive blood cultures. The number of Escherichia coli strains causing neonatal sepsis resistant to the antibiotics used in the treatment is increasing. In this study, two E. coli strains causing sepsis in neonates of mothers infected with an E. coli strain harboring extended spectrum beta-lactamases were characterized. The blaCTX-M-15 and the blaCTX-M-14 genes were found in an IncFIA and nontypeable transferable plasmids, respectively. In addition, these highly virulent strains belonged to ST705 and ST156 clonal groups, respectively. The presence of strains, which are highly virulent and resistant to ampicillin, gentamicin, and cephalosporins, makes a change in empirical treatment necessary as well as an increase in the surveillance of these infections.