hint:burst not implode

Ok, penicillin prevents cell wall formation of bacteria due to osmotic pressure and digestion of peptidoglycan (structural strength of the cell wall). Now you have to pick your bacteria. The bacteria in question could be GRAM-POSITIVE or GRAM-NEGATIVE.

Gram-positive bacteria are called PROTOPLASTS when they COMPLETELY lose their cell wall. During digestion of the cell wall, the protoplast becomes very sensitive to osmotic stress. If the bacteria were in a HYPOtonic solution – the plasma membrane (cell membrane/phospholipid bilayer) would burst (cytolysis). If the bacteria were in a HYPERtonic solution, the plasma membrane would weaken and/or collapse and be “paralyzed” (plasmolysis). To prevent rupture of the cell membrane, the bacteria would have to be in an isotonic solution.

Gram-negative bacteria are called SPHEROPLASTS and DO NOT completely lose their cell wall. During digestion of the cell wall, the spheroplasts are also sensitive to osmotic stress. If the bacteria were in a HYPOtonic solution – the cell membrane would burst (cytolysis). If the bacteria were in a HYPERtonic solution, the plasma membrane would weaken and/or collapse as well. So, the bacteria would have to be in an isotonic solution here as well to have any chance of “living”.