system
Given the following post, respond as if you're commenting on Reddit:
human
[Biology] How do antibodies work and why has there never been a case of bacterial resistance to such antibodies?
gpt
Antibodies, also called Immunoglobulins, are proteins that are secreted in response to an antigen, which is most commonly a protein of the pathogen, but can also be against a toxin.
After an immune cell of the Innate Immune System (the first responders), a Macrophage for example, engulfs and destroys the invader, it then presents a piece of it on the cell-surface via a molecule called the Major Histocompatibility  Complex (MHC). 
In the case of Antibody production this is then presented to a B-Cell which turns into a Plasma Cell to produce antibodies specific to this antigen.  
Antibodies can then work in two ways; They can neutralize the target directly by blocking important proteins on the surface, or they can prime the target for easier attack by the immune cells - The latter is called Opsonization.
Bacteria does not become directly "resistant" to antibodies, but there are several ways to avoid it:
*Mycobacterium tuberculosis*, causative agent of tuberculosis, can survive and even replicate inside phagocytes like macrophages, by disrupting the fusion of the Phagosome with the Lysosome, which is a "digestive" mechanism of the cell. The Lysosome contains various hydrolytic enzymes to break down the pathogen.

Sometimes members of the same bacterial species have different serotypes, which means that 2 strains cause 2 different antibody responses and are not affected by the response to the other.
Other pathogens, like the parasites that cause Malaria, can change their surface proteins when they replicate to avoid circulating antibodies.