Most of the people on this forum believe that their UC flares began shortly after taking antibiotics. They are probably right. One possible theory is that antibiotics are weapons of mass destruction that kill both the bad bacteria, and the good bacteria in your gut.
The good bacteria are what keep the bad bacteria in check and under control. But when the antibiotics are ended then the bad bacteria grow back more quickly and become the majority, thus creating all sorts of intestinal disorders including C Diff and ulcerative colitis, (maybe Crohn's too).
So a popular recommendation is to take probiotics every day about
3 hours after antibiotics to replenish the good guy bacteria and maintain balance. An excellent probiotic to take WHILE using antibiotics is S. Boulardii. It works because it is not a bacteria at all but a probiotic yeast that is immune to antibiotics. Thus it stays alive to keep the bad guys in check. It is particularly effective against C. Diff bacteria. But all probiotics are good.
Having said that, I am one of those people who took antibiotics that jump-started me into remission from a serious flare. And I am not the only one, check out this link. Triple Antibiotic Therapy has worked for many on this forum. Apparently it kills the bad guys that cause UC, but it doesn't work for everyone. The best advice is if you have to take antibiotics then make sure you are also taking probiotics with them.
www.healingwell.com/community/default.aspx?f=38&m=2088679