Introduction Bacterial virulence intrinsic characteristics that influence the bacteria's ability to infect a host methods of increasing virulence Bacterial Virulence Factors and Examples Virulence Method Bacterial Examples Factors Function Adhesion and colonization Streptococcus pneumoniae Haemophilus influenzae type b Neisseria spp. IgA protease Cleaves IgA and allows the bacteria to adhere and colonize mucous membranes Adhesion and colonization Escherichia coli Fimbriae Helps adhere and attach to host cells Invasion Obligate and facultative intracellular organisms (i.e., Chlamydia spp.) Unknown factors Helps the bacteria invade host cells Evades immune response by the host Staphylococcus aureus Protein A Prevents phagocytosis by binding to the Fc region of IgG Evades immune response by the host Group A streptococcus Protein M Prevents phagocytosis Evades immune response by the host Streptococcus pneumoniae Capsule Prevents phagocytosis Toxins Gram-negative bacteria Endotoxins Exerts many effects, including activation of the complement system, macrophages, and tissue factor Causes sepsis and disseminated intravascular coagulation Toxins Some gram-negative and gram-positive bacteria Exotoxins Various effects, depending on the exotoxin, including host cell death, mucosal damage, diarrhea, and neurotoxicity