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: CASE SUMMARY : A 13 - year - old boy was treated with ampicillin and gentamicin because of suspected septicemia .
### Output Text:
CASE SUMMARY : A 13 - year - old boy was treated with <span class="chemical">ampicillin</span> and <span class="chemical">gentamicin</span> because of suspected septicemia . 