01-21-2014, 04:40 AM
a culture of staphylococcus aureus bacteria is selected over many months for its ability to grow in increasing concentrations of penicillin. when colonies of this original culture are capable of growth on blood agar containing 400,000IU penicillin, the colonies are picked from the agar, placed in a nutrient broth, and a lytic phage is added. the bacteria and phage are co-cultured until viral maturation is complete. the culture is centrifuged and the supernatant liquid is added to culture tubes containing clones of penicillin-sensitive S. aureus. after 4 hours of incubation at 37 C. these broth cultures are dumped on to the blood agar petri dishes containing 400,000 IU penicillin and incubated for 24 hours. out of 100 petri dishes, 4 grow colonies. what process has taken place in the experiment?