seekeerz
Sorry about the problem that your husband had, it sounds quite nasty.
<<< having been off his food and now needing two or three trips to the bathroom each day.<<<
By that I gather that he is having diarrhoea, in which case it is almost certainly secondary to the antibiotics and should settle within the next few days. I have to confess that I am not a fan of either probiotics or any other" immune system booster"
and providing that he drinks plenty to combat the diarrhoea, he should pick up quite quickly.
Sorry to sound a bit negative, but your husband is right...it will take time.