The bacterial cell wall — a vulnerable shield

Abstract

In the search for differences between bacteria and animal cells that could provide the basis for a selective antibacterial attack, one evident distinction lies in their general structure. The animal cell is relatively large and has a complex organization; its biochemical processes are compartmentalized and different functions are served by the nucleus with its surrounding membrane, by the mitochondria and by various other organelles. The outer membrane is thin and lacks rigidity. The cell exists in an environment controlled in temperature and in osmolarity and it is constantly supplied with nutrients from the extracellular fluid bathing it. The smaller bacterial cell lives in a variable and often unfavourable environment. In particular it must be able to withstand considerable changes in osmolarity. Some bacteria have relatively high concentrations of solutes of low molecular weight in their cytoplasm. Such a cell suspended in water or in dilute solutions will develop a high internal osmotic presure. This would inevitably disrupt its membrane unless it were provided with a tough, rigid outer coat. This coat is the cell wall, a characteristic bacterial structure entirely lacking in animal cells. It has a protective function for the bacterium, but at the same time it is vulnerable to attack, and a number of effective antibacterials owe their action to their ability to disturb the processes by which the wall is synthesized. Since there is no parallel biosynthetic mechanism in the animal cell, substances affecting this process may have quite a low toxicity.