Horizontal Gene Transfer: You have isolated a strain of E. coli that is resistant to the antibiotics penicillin, streptomycin, chloramphenicol, and tetracycline. You observe that when you mix this strain with cells of an E. coli strain that is sensitive to the four antibiotics, the sensitive strain becomes resistant to streptomycin, penicillin and chloramphenicol but remains sensitive to tetracycline. Explain these results