Suggest Cure For E Coli Infection

my baby was hospitalised for high fever and found out its due to e coli thru urine sample..he was given 5 days of rocephine and follow by 3 days antibiotics after discharged. My baby redo d urine test and e coli still exist. Most antibiotics were susceptible according to d test but when we did another urine test two weeks later, he is resistant to cedax, rocephine, zinacef and augmentin.what s d best thing to do now? Circumcision?