Group A streptococci are able to synthesize a capsule composed of hyaluronic acid. Many important pathogenic bacteria bear on their surfaces substances that inhibit phagocytic adsorption or engulfment. Clearly it is the bacterial surface that matters. Protein A produced by Staphylococcus aureus . Thus, the ability of IgG to act as an opsonic factor is inhibited, and opsonin-mediated ingestion of the bacteria is blocked.
Some bacteria survive inside of phagocytic cells, in either neutrophils or macrophages.
Bacteria that can resist killing and survive or multiply inside of phagocytes are considered intracellular parasites. In this case, the environment of the phagocyte may be a protective one, protecting the bacteria during the early stages of infection or until they develop a full complement of virulence factors. The intracellular environment guards the bacteria against the activities of extracellular bactericides, antibodies, drugs, etc. Some bacteria that are intracellular parasites are listed in Table 1. Intracellular pathogens such as Yersinia , Listeria , Salmonella , Shigella and Legionella possess complex machinery for cellular invasion and intracellular survival.