Hemolysis by the important alpha-lysin is detected by the use of sheep or rabbit erythrocytes. The delta-lysin also hemolyzes rabbit erythrocytes. Human red cells are not lysed by the alpha-lysin. Mannitol Salts Agar contains mannitol as a fermentable carbohydrate, the indicator phenol red for detection, and a high concentration of salt to inhibit undesired organisms. It has been observed that coagulase positive staphylococci grew luxuriantly, producing yellow-gold colonies with yellow zones.
Nonpathogenic staphylococci produce small colonies with no color change of the surrounding medium.
Other bacteria are generally inhibited, making possible the use of a heavy inoculum without danger of overgrowth. Incubation for 24-36 hours at 37C is recommended. Prepare a gram stain. Microscopically observe under the oil immersion objective. Describe your observations.