Medical_Bacteriology_III.pdf

1 Bacterial Virulence Factors  5. Bakteriyel Virülans Faktörleri Dr. Özge YILMAZLI 2 Bacterial Virulence Factors  For a bacterium, the human body is a collection of environmental niches that provide the warmth, moisture, and food necessary for growth  Bacteria have features that enable th...

1 Bacterial Virulence Factors  5. Bakteriyel Virülans Faktörleri Dr. Özge YILMAZLI 2 Bacterial Virulence Factors  For a bacterium, the human body is a collection of environmental niches that provide the warmth, moisture, and food necessary for growth  Bacteria have features that enable them to enter (invade) the environment, remain in a niche (adhere or colonize), access to food sources (degradative enzymes) and escape clearance from host immune responses (e.g., capsule)  Many of these features are virulence factors that enhance the ability of bacteria to cause disease  Pathogen: A microorganism that capable of causing disease  Pathogenicity: The ability of an infectious agent to cause disease  Virulence is defined as the degree of pathogenicity of a pathogen and is determined by its ability to invade and increase within the host. 3 Bacterial Virulence Factors Bacterial Virulence Factors 4 Bacterial Virulence Factors 5 Bacterial Virulence Factors Entry into the Human Body:  For infection, bacteria must entry into the body first  Natural defense mechanisms which are barriers (e.g., skin, ciliated epithelium) and secretions (mucus, …) containing antibacterial substances to make it difficult for bacteria to entry into the body  However, these barriers are sometimes broken and providing a portal of entry for the bacteria, or the bacteria may have the means to compromise the barrier and invade the body  The mouth, nose, respiratory tract, ears, eyes, urogenital tract, and anus are sites for bacteria can enter the body 6 Bacterial Virulence Factors Adherence:  When bacteria enter the body of the host, they must adhere to cells of a tissue surface. If they did not adhere, they would be swept away by mucus and other fluids while washing the tissue surface  Some bacteria have pili, shorter “hairlike” structures that extend from the bacterial cell surface and help mediate adherence of the bacteria to host cell surfaces 7 Bacterial Virulence Factors Invasion:  Invasion is the term commonly used to describe the entry of bacteria into host cells  Many species of invasive bacteria produce enzymes that are not intrinsically toxic but play important roles in the infectious process  Collagenase and Hyaluronidases are enzymes that hydrolyze hyaluronic acid and collagen, constituent of the ground substance of connective tissue. They are produced by many bacteria and help in their spread through tissues  Hemolysins are enzymes that cause lysis of red blood cells  Coagulase causes accumulation of fibrin on the surfaces of individual Staphylococcus aureus , which may help to protect them from phagocytosis or from destruction within phagocytic cells. 8 Bacterial Virulence Factors  Toxins:  Toxins are bacterial products that directly harm tissue or trigger destructive biological activities  Toxins produced by bacteria are generally classified into two groups  Exotoxins  Endotoxins Bacterial Virulence Factors Bacterial Virulence Factors 11 Bacterial Virulence Factors mostly gram + Exotoxins  Exotoxins are proteins that can be produced by gram positive or gram negative bacteria  Most exotoxins are composed of A and B subunits linked by disulfide bonds  A subunitis responsible for toxic activity  B subunit is responsible for binding the protein to the host cell and entering into the cell  Vaccines have been developed for some of the exotoxin-mediated diseases and continue to be important in the prevention of disease  These vaccines—called toxoids—are made from exotoxins, which are modified so that they are no longer toxic Bacterial Virulence Factors 13 Bacterial Virulence Factors Endotoxins  They are the lipid portions of lipopolysaccharides (LPS) that are part of the outer membrane of the cell wall of Gram (-) bacteria  They are liberated when the bacteria die and the cell wall breaks apart  They are heat stable  They can not be toxoided  Stimulate the development of protective responses such as fever, vasodilation, and activation of immune and inflammatory responses 14 Bacterial Virulence Factors