My Husband Had His Leg Amputated Due To Flesh Eating

My husband had his leg amputated due to flesh eating disease in 2009, since then has had a hip distartculation and infections. Apparently they bacteria is coming from his bowel, and gut. He has been on and off antibiotics since the intial amputation, Why does these infections keep recurring, He has and still is on the big gun antibiotics, meropenam, fluconazole, pipacillin, etc. We are at are wits end trying to find how to stop these from coming back, Once he is off the antibiotics, he has a couple of months of being ok and then they come back