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: Despite the widespread use of these agents this triad of side effects has not previously been reported in connection with beta lactam antibiotics .
### Output Text:
Despite the widespread use of these agents this triad of side effects has not previously been reported in connection with <span class="chemical">beta lactam</span> antibiotics . 