You have isolated a strain of e. coli that is resistant to penicillin, streptomycin, chloramphenicol, and tetracycline. you also observe that when you mix this strain with cells of e. coli sensitive to the four antibiotics, they become resistant to streptomycin, penicillin, an chloramphenicol, but remain sensitive to tetracycline. explain what is happening. be thorough and complete in your answer.