What does it indicate when a bacterium is coated by antibodies?

When a bacterium is coated by antibodies, this signifies that the antibodies are marking the bacterium for destruction by immune cells. The coating of antibodies, also known as opsonization, enhances the ability of phagocytic cells, such as macrophages, to identify and engulf the bacterium. This process is crucial for eliminating pathogens from the body.

The presence of antibodies on the bacterium indicates that the immune system recognizes it as a potential threat. Macrophages can bind to the antibodies via their Fc receptors and subsequently endocytose the bacterium, leading to its degradation and clearance. Therefore, such a coating does not mean the bacterium is viable or escaping immune detection; instead, it highlights a response to eliminate the bacterium from the host.