Purpose: The purpose of the study is to investigate if treatment with ciprofloxacin for one week followed by therapy with E. Coli Nissle (EcN) for seven weeks can influence disease activity among ulcerative colitis patients with disease flare-ups compared to placebo controls.

Ulcerative colitis (UC) is a chronic inflammatory bowel disease where existing treatments have proven to result in numerous side effects. An important causal factor for the development of the disease is an autoimmune cellular response against bacteria in the colon.

As a possible treatment, manipulation of the bacterial flora has been studied using the probiotic bacterium Escherichia coli Nissle 1917 (EcN). Studies on UC patients have shown that treatment with EcN is equally good at maintaining remission as the standard treatment with mesalazine. Furthermore, treatment with antibiotics such as ciprofloxacin have been studied for treatment of UC and some, but shortlived, effect has been described.

Patients are randomized to one of four treatment-arms: ciprofloxacin-EcN, ciprofloxacin-placebo, placebo-EcN or placebo-placebo.

Disease activity are quantitated with Colitis Activity Index (CAI) and quality of life by the Inflammatory Bowel Disease Questionnaire (IBDQ). Also, dietary interviews to examine the patients' dietary intake are completed and the patients' fecal-calprotectin-concentrations will be measured.

Hundred subjects with ulcerative colitis will be recruited for the study. Standard medical care and therapies will be continued throughout the study

Inclusion Criteria:

• Age, >/=18 years and diagnosed with ulcerative colitis
• CAI score of >/=6 (active UC)

Exclusion Criteria:

• Pregnant or breastfeeding females
• Known sensitivity to ciprofloxacin
• Subjects who participate in another clinical trial
• Positive stool sample with any enteric pathogens, parasites or Clostridium difficile
• Treatment with systemic corticosteroids or biologic therapy