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Bacteria research. Agar plate of cultured methicillin-resistant Staphylococcus aureus (MRSA) bacteria, viewed through a magnifying lens. On the laboratory bench are different types of agar plates, including chocolate agar (dark red), blood agar (red) and cled agar (green). The different types are used to isolate and grow different types of bacteria during hospital pathology tests. Blood and chocolate agar are used for blood samples, whereas cled agar is used for urine samples. The agar provides the nutrients required by the bacteria. Hospital microbiology laboratories identify pathogenic bacteria from samples to help doctors diagnose disease. (KEYSTONE/SCIENCE PHOTO LIBRARY/SOTIRIS ZAFEIRIS)