What is the function of a Gram-negative bacterium's outer membrane?

The outer membrane of a Gram-negative bacterium plays a critical role in the organism's survival and pathogenicity. One of its primary functions is to provide a barrier against various harmful substances, including antibiotics and host immune defenses. This barrier helps the bacterium to maintain its integrity and protect itself from the effects of external threats. The presence of porins in the outer membrane allows selective passage of certain molecules, contributing to the bacterium's ability to control what enters and exits the cell.

This protective function is especially important for Gram-negative bacteria, as they can be more resilient to antibiotics compared to Gram-positive bacteria, which lack this outer membrane. By limiting access to the underlying cell membrane, the outer membrane contributes significantly to the bacterium's antibiotic resistance mechanisms, posing challenges in treating infections caused by these organisms.