A microbiologist transfers and inoculum from a slantlabeled Staphylococcus aureus on to a Petri plate. Following in cubation, both Staphylococcus aureus and Escherichia coli aredetermined to be growing in this culture. What is the most likely explanantion?

a. the microbiologist used a complex media
b. the culture is contaminated
c. the incubation temperature was incorrect
d. the culture medium must be selective
e. the culture medium must be differential