pathogenesis

Fig KOCH’S POSTULATES Tools: Diseased animal Healthy animal Red blood cell Observe blood/tissue under the microscope Red blood cell The Postulates: 1. The suspected pathogenic organism should be present in all cases of the disease and absent from healthy animals. 2. The suspected organism should be grown in pure culture. Suspected pathogen Microscopy, staining No organisms present Streak agar plate with sample from either diseased or healthy animal Colonies of suspected pathogen Laboratory culture 3. Cells from a pure culture of the suspected organism should cause disease in a healthy animal. Experimental animal Diseased animal Inoculate healthy animal with cells of suspected pathogen Remove blood or tissue sample and observe by microscopy Laboratory culture Suspected pathogen Laboratory reisolation 4. The organism should be reisolated and shown to be the same as the original. Pure culture (must be same organism as before)

Primary pathogens: Cause disease in healthy hosts Opportunisitc pathogens: Cause disease only in immunocompromised patients Virulence is a measure of the severity of a disease. - Infectious dose vs. lethal dose Figure 25.5

Figure 25.6

Figure 25.11Figure 25.13A

Table 28-3

Figure Bacteria can attach to surfaces in bulk, forming a biofilm. - Play important roles in chronic infections Figure 25.15A Streptococcus pyogenes M protein Bordetella pertussis Pertactin

Figure 25.16

AB Toxins B subunit: Binds to host cell - Delivers A subunit to cytoplasm - Often five B subunits form a pore for A entry. Figure 25.17B A subunit: Has toxic activity - ADP- ribosyltransferase - Diphtheria toxin - Cholera toxin Figure 25.17A

Figure 13.7A

Figure 25.20

Animation: Cholera Toxin Mode of Action Click box to launch animation ADP-Ribosylating Toxins

Alpha Toxin The hemolytic alpha toxin is produced by Staphylococcus aureus. - Forms a transmembrane, seven-member pore in target cell membranes Figure 25.18

Anthrax Toxin Made by Bacillus anthracis Two active toxins: - Edema factor raises cAMP levels. - Causes fluid secretion, tissue swelling - Lethal factor cleaves protein kinases. - Blocks immune system from attacking Figure 25.21C

Endotoxins Made only by Gram-negative bacteria Present in lipopolysaccharide of outer membrane - Lipid A released as bacteria die - Causes massive release of cytokine from host cells - Can trigger fever, shock, and death Figure 25.22

Figure 25.31

Figure 25.32

Figure 25.29