No you don't get bacteria or diseases from oil pulling. It actually removes harmful bacteria (or kills it in the case of oregano oil or even coconut oil).
In fact when i get sick I usually pull with a few drops of oregano oil to help with the infection.
By the way, when I get bronchitis (or pneumonia) I put Colloidal Silver , mullein and lobelia extract in a nebulizer and nebulize three times a day. I find it knocks it out slightly faster than Antibiotics and doesn't harm the body the way Antibiotics do.
In fact for many years I got bronchitis at least once a year and used Antibiotics . Once I started using the nebulizer and Colloidal Silver I get it much less often.