The predatory bacterium Bdellovibrio bacteriovorus drills into a prey bacterium and, once inside, digests it. When the predatory bacterium attacks the gram-negative bacterium, what are the first structures penetrated by B. bacteriovorus on its way into the prey's cytoplasm

The outer membrane, a peptidoglycan layer, periplasm, and cell membrane

Explanation:

The predatory bacterium will have to penetrate the cell wall and the cell membrane of the gram-negative bacterium before getting access to the cytoplasm.

In order to penetrate the cell wall of a gram-negative bacterium, the predatory bacterium will have to penetrate the components of the cell wall which consists of an outer membrane, a thin peptidoglycan layer, and a gel-like matrix known as the periplasm.

Thereafter, the predatory bacterium will have to penetrate the cell membrane before eventually getting access into the cytoplasm of the prey bacterium.

i think its both a and b