Phosphorylation of the hydroxyl groups of viomycin. Hydrolysis of the beta-lactam ring of penicillins. Overproduction of dihydrofolate reductase in response to trimethoprim. All of the above are correct. They are not readily absorbed into eukaryotic cells.
Bacteria possess porins that allow access of bet-lactams to the target enzymes.
Eukaryotic organisms do not possess porins. Eukaryotes neither possess a peptidoglycan cell wall nor the supporting enzymes to produce it. These bacterial enzymes are the target for the beta-lactams. Any beta-lactam that is absorbed into mammalian tissue is rapidly inactivated by endogenous, cytoplasmic peptidases. None of the above.