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: In rhesus monkeys , intravenous challenge with 0 . 6 x 10 ( 10 ) to 2 . 2 x 10 ( 10 ) Pseudomonas aeruginosa organisms caused acute illness of 4 to 5 days ' duration with spontaneous recovery in 13 of 15 monkeys ; blood cultures became negative 3 to 17 days after challenge .
### Output Text:
In rhesus monkeys , intravenous challenge with 0 . 6 x 10 ( 10 ) to 2 . 2 x 10 ( 10 ) Pseudomonas aeruginosa organisms caused acute illness of 4 to 5 days ' duration with spontaneous recovery in 13 of 15 monkeys ; blood cultures became negative 3 to 17 days after challenge . 