Hello Doctor, My Father Age 66, Went Through An Prostrate

Hello Doctor,
My Father age 66, went through an Prostrate Surgery in six months back.. last month he had severe fever and we later found that it is because of Urinary tract infection, we did a culture test and identifed
ESBL E.Coli isolated in culture > 0000 CFU/ml.
Later he went through antibiotics and his fever came down and took medicine for another month..
We aging took the culture but still the infection was not reduced and doctor advised not to take any further medicine and advised to take plenty of water and come back incase if thereis any signs of Fever or irritation while passing urine..

Since yesterday he again has fever.. not sure if its again because of this infection.. my question is does this infection will harm and spread to other organs as it was not fully cured and doctor advised to stop medicine..
Please suggest what needs to be done..