It's not you that's resistant to ABX, it's the germ-critters that are resistant to the ABX! So with time things can change depending on the specifics of exactly what infections your cultures are growing. When they do the culture sensitivity testing they grow the germs from your culture, and then treat them in a petri dish (or whatever) with the basic classes of antibiotics. They then count how many the ABX killed, or how many are remaining. THat determines the sensitivity of the germ to that particular ABX. That's provided in a report to your doctor who ordered the culture test. It's not a perfect process and you could be growing more things than what was in the sample you provided to the lab. Plus some of the germs mutate over time so even if you didn't fully eradicate them with one specific ABX, over time the germ may change somewhat, so 6 months or a year later that ABX might work again. ~Juliet