Ozone located in the troposphere is . a. considered a pollutant b. beneficial to living organisms c. higher in concentration than ozone in the stratosphere d. all of the above

Consider a culture medium on which only gram-positive organisms such as staphylococcus aureus colonies can grow due to an elevated nacl level. a yellow halo surrounds the growth, indicating the bacterium fermented a sugar in the medium, decreasing the ph as a result and changing the color of a ph indicator chemical. this type of medium would be referred to as a differential and enrichment culture.