Final answer:
Peptidoglycan synthesis is the most selective target for antibiotic action regarding toxicity due to the absence of this pathway in human cells and its critical role in bacterial cell wall integrity.
Step-by-step explanation:
Among the given targets for potential antibiotic action, peptidoglycan synthesis would be expected to be the most selective with respect to toxicity. This is because it targets a unique feature of bacterial cells, their cell wall, which is absent in human (eukaryotic) cells. Peptidoglycan is a critical component of bacterial cell walls, and inhibiting its synthesis causes bacterial cells to become more prone to osmotic lysis due to the weakening of the structural integrity of the cell wall.
Other targets such as the 70S ribosome, DNA synthesis, glycolysis, and cytoplasmic membrane function also provide selectivity since they either differ structurally between bacteria and humans or are more essential to bacterial survival.