Page 854 - Veterinary Immunology, 10th Edition

Another useful skill for a bacterium to possess is the ability to
VetBooks.ir resist antibacterial peptides. For example, staphylokinase from S.

aureus can bind and neutralize defensins. Another staphylococcal
enzyme, aureolysin, destroys cathelicidins. Salmonella and S. aureus

can produce proteins that change the negative charge and fluidity
of the bacterial outer membrane resulting in decreased defensin
binding. Klebsiella pneumoniae capsular polysaccharide blocks β-
defensin expression by airway epithelial cells. Proteases from

Bacillus anthracis can destroy defensins and cathelicidins.
Many bacteria can block phagocytosis (Fig. 26.6). For example, S.
aureus expresses protein A. Protein A attaches to IgG Fc regions and
so prevents antibodies from binding to Fc receptors on phagocytic

cells or activating the classical complement pathway. Encapsulated
bacteria such as pneumococci possess a hydrophilic capsule that
cells cannot bind. Many bacteria can evade opsonization by
complement. Thus the M protein of streptococci binds fibrinogen

and masks C3b-binding sites. It also binds factor H, and so
inactivates bound C3b. S. aureus produces a protein that blocks C3
convertases. Other bacteria produce proteases that can destroy
complement components. S. enterica Typhimurium has a gene

called Rck that confers resistance to complement-mediated lysis by
preventing insertion of the terminal complement complex into the
bacterial outer membrane.

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