If someone gave you oral sex with bad bacteria or saliva , how long would it take for them to go away or die ?

Low STD risk: This depends on what you mean by "bad bacteria". If the person had an STD like gonorrhea, you could have been infected. However, normal bacteria in the mouth don't cause any harm. Oral sex is safe sex -- not completely free of risk, but much safer than vaginal or anal sex. However, if you are in doubt or worried, it's always best to get STD tested.