A colonic tissue culture is a laboratory test performed on a specimen of colon (large intestine) tissue to isolate and identify organisms that may be causing certain infections (e.g., infectious diarrhea, parasitic and viral infections involving the colon). The specimen is obtained by a colonoscopy . A colonoscopy is a procedure for viewing the interior lining of the large intestine (colon) using a colonoscope, a flexible fiber-optic tube about 1/2 inch thick.