Do you realize you have streptococcus bacteria in your throat right now? This is the same bacterium that is present in extreme cases of strep throat. Yet you may not have strep throat. In fact you may not even have a sore throat.
Why?
Well, because the strep bacteria doesn't actually cause strep throat. Strep throat is actually caused by a buildup of toxins in the throat and tonsils. Strep bacterium feeds on these toxins. It is only when this bacteria food builds up that the bacteria is able to flourish and run wild.
In fact you won't get strep throat or tonsillitis no matter how much bacteria you're exposed to until the conditions in your throat are right for them to flourish.