I think that may actually be worse than if the dirt didn't contain any. Antibiotics only work well when the dose is strong enough and taken for a long enough pe

I think that may actually be worse than if the dirt didn't contain any. Antibiotics only work well when the dose is strong enough and taken for a long enough period, anything less leads to the original problem being fought with no real benefit for having ingested them. There is a similar concept for that kind of saying called the "hygiene hypothesis" though, but it's often taken too far to the extremes from what it's trying to claim.