In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Treatment of Crohn ' s disease with fusidic acid : an antibiotic with immunosuppressive properties similar to cyclosporin .
### Output Text:
Treatment of Crohn ' s disease with <span class="chemical">fusidic acid</span> : an antibiotic with immunosuppressive properties similar to <span class="chemical">cyclosporin</span> . 