I have no personal experience of foulbrood but seem to remember being taught that  this was a disease of the brood and it did not effect the bees which remained healthy.  The treatment as I recall was to shake all the bees into a box and shut them in allowing sufficient ventilation and to starve them for a given period ( I remember asking how long they had to be starved and was told "Until they begin to die!!").  The bees are then hived  on fresh foundation.  The old frames have to be burned and all the exposed hive parts scorched .
 
Harry