Hardiness of Aquarium Bacteria

Not a newbie, but I sure feel as confused as one =)

How hardy are the bacteria that turn ammonia into nitrite and nitrite into nitrate?

When the last of my old fish died, I rinsed my ten gallon in very cold (and some parts in very hot) tap water and chose to cycle with a quartet of Black Skirt Tetras, because I can't stand an empty tank (Don't worry for them, I've been doing 2-3 25% water changes daily, figuring it would slightly delay the cycle, but also help them out, no gravel vaccing).

I finally got a chance to get test kits today, the black skirts have been in there four days now, so I expected to see my ammonia spike. However, the results came out Ammonia 0, Nitrites < .25ppm, and I'm confused. Do you think I should go find another test kit and double check? Either they aren't producing ammonia, or the ammonia eating bacteria are already established, or maybe something else is going on...

Other tank stats: 78F, I add one drop of Seachem Prime to each gallon of new water, as per the instructions, no other additives.

What are your thoughts?

Actually, I'm trying desperately to get hold of some of the stuff. If nothing else, I want to give it a test run to see if I could make use of it in setting up an aquarium quickly in my dorm next year.

The supplier here in CO doesn't have it yet, but several LFS people here in town, and in Denver are bugging their sales reps, the hope is to have some in by the end of the month, hopefully earlier. It may not help me with this aquarium, but I think I'll buy some anyway just to test on an empty aquarium with a fishless cycle. =)

I am surprised those little bacteria could survive a scrubbing like that, they must be tougher than I thought.