I repeated a culture twice in an entry level microbiology class for our final lab project of culturing a provided unknown organism. One of the required tests on our dichotomous key was to culture a gram positive cocci in mannitol salt agar. After repeating the experiment twice as instructed, and doing an isolation streak as instructed, the part of the agar with no growth was acidic while the part of the agar with growth was neutral or slightly basic. Both cultures were incubated for around 48 hours, and the first one then refrigerated for another 48 hours while the second one was examined directly after incubation. My professor told me to disregard the results and treat it as a negative in my report, but I'm perplexed as to how this result came about.