Treated for antibiotic-induced colitis. Do I need to supplement with probiotics?

You can try.... Apart from certain probiotics such as saccharomyces boulardii, in clinical testing. Most probiotics are inconsistent in their effectiveness in restoring normal intestinal flora functioning. It may work in some people, but not in others. In most cases, it doesn't harm the patient- but is it worth the extra health resource dollars, is debatable. .
Yes. Take a high quality probiotic such as Probonix (8-10 drops) daily for 3 months. This one is available at AMazon.com only. Using probiotics daily may reduce your chances of catching infections in general.