“Because Gram-positive bacteria have only a single cell wall, even though it’s thicker, they are, in general, much easier to treat. With Gram-negative bacteria, two cell walls have to be penetrated, not just one. In essence, the bacteria have two chances to identify and deactivate an antibacterial that is hostile to them. Even if an antibiotic gets into the periplasmic space, it usually will not kill the bacteria. It still has to penetrate the second wall.”
