Yes, the answer is constantly: bacteria are common in the air, water, just about everything we eat, on our skin, and inside of our body spaces. However, most of these assaults are accidental or relatively benign - we happen to inhale bacteria with no adaptations to be infectious, so our immune systems quickly mop them up with no need of antibodies or t-cells. The nasty things assault us less frequently, but still pretty often, daily at the least.