> no trace of the type of bacteria that was contained in my probiotic that I had been taking religiously for a long time.
That's not how it works. The probiotic you took was full of bacteria DNA (maybe, probiotics rarely hold up to their advertised claims) which had to make it through your stomach, several meters of small bowel, and then to your large bowel. The DNA in that probiotic was likely snipped apart so many times its just in the noise at this point.
Fun fact: your small bowel and large bowel have significantly different biomes. Your small bowel has more in common with mouse stool than it it doesnt with your small bowel!
Anecdata: I've had the unfortunate need to have my gut biome taken a look at. Honestly, I'm not certain how the process was done, but my pro-biotic at the time showed up clearly in the results I was given.
Total scam from start to finish. Throw the book at them.