I almost forgot to mention the most important thing. The strep screen tests are just that, a screen. If they are positive then fine, but most of them are negative.
We do follow up throat cultures on all negative strep screens, that where we catch most of the streps. Not sure about doctor offices, I work in a hospital laboratory in microbiology.
This is what group A strep (strep pyogenes, the one that causes the bad strep throat) looks like on a blood agar plate. This specimen was from a tissue culture, it's really bad when it gets into your tissues. There is a lot of normal flora in the throat, those plates don't look as pretty.
The clearing you see around the colony is called "hemolysis". Beta hemolysis to be exact.
There is more than one beta hemolytic strep that causes problems for people but strep pyogenes is the worst. That's also one of the "flesh eating bacteria" strains. A fireman had to have a limb amputated a couple years ago when a leg wound got infected. There isn't competition from normal flora when it get's into your tissues, those infections tend to be more serious. The organism secrets toxins which damage tissue and also hinder the ability of the white cells to get to the wound, which makes the organism grow even more. The damage to the tissues can make treatment difficult.
It's easily treated with any of the penicillins (unless it gets bad).