Which of the following antibiotic resistance mechanisms are most likely to be encoded by a single gene or operon that could be transferred between bacteria?
a. An enzyme that modifies an antibiotic so it can no longer bind its target
b. The hydrophobic outer membrane of Gram-negative bacteria
c. An alteration in the antibiotic's binding site on its cellular target An enzyme that processes antibiotics to inactivate them
d. A mutation in the DNA regulating gene expression that results in fewer antibiotic-accessible membrane porins in the cell wall
e. A membrane transporter that actively pumps antibiotics out of the cell