SUPER LAB Micro Questions With Complete Solutions

*Selective:* Selects for: Gram (+) *Components:* Phenylethyl alcohol (used for isolation of Gram + from mixed cultures) Plate A is a PEA plate with a Gram positive organism on the left and a Gram negative organism on the right. Plate B is a nutrient agar plate illustrating normal growth of each of the same bacteria. Notice that the Gram-negative organism shows inhibited growth on the PEA plate. Phenylethyl Alcohol agar (PEA/PAA) Phenylethanol Agar (PEA) Phenylethanol inhibits many Gram negative bacteria and its inclusion in PEA renders the medium selective for Gram positives. PEA/PAA agar *Components:* 7.5% NaCl; Mannitol; Phenol Red pH Indicator *Selective for:* 7.5% NaCl growth ( Staphylococcus sp) *Differential for:* Mannitol fermentation phenol red turns yellow *Results* Growth: Staph sp and specific other sp. *Fermentation/Acid* If bacteria ferments mannitol the phenol red indicator turns yellow Mannitol Salt Agar (MSA) orange arrow points to positive mannitol fermentation and positive growth Blue arrow points to negative fermentation and positive growth MSA Positive and Negative Results S. aureus is positive for fermentation S. epidermidis is negative for fermentation MSA S. epidermidis and S. aureus comparison