A 20-year-old male had pain in abdomen and mild fever followed by gastroenteritis. The stool examination showed the presence of pus cells and RBC&;s on microscopy. The etiological agent responsible is most likely to be

`Enteroinvasive E.coli: invade intestinal cells in vivo. The ability to penetrate the cell is determined by the large plasmid. Clinically EIEC infection resembles shigellosis, the passage of bloodstained mucopurulent stools. HeLa and HEp-2 cell invasion in culture can also be used as a diagnostic test. Reference: Textbook of Microbiology; Anathanarayan and paniker's; 10th edition; Page no: 285