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pathogenesis Fig. 1-15 KOCH’S POSTULATES The Postulates: Tools: 1. The suspected pathogenic organism should be present in all cases of the disease and absent from healthy animals. Microscopy, staining 2. The suspected organism should be grown in pure culture. Laboratory culture Diseased animal Red blood cell Observe blood/tissue under the microscope Suspected pathogen Streak agar plate with sample from either diseased or healthy animal Colonies of suspected pathogen Healthy animal Red blood cell No organisms present Inoculate healthy animal with cells of suspected pathogen 3. Cells from a pure culture of the suspected organism should cause disease in a healthy animal. Experimental animal Diseased animal Remove blood or tissue sample and observe by microscopy 4. The organism should be reisolated and shown to be the same as the original. Laboratory reisolation Suspected pathogen Laboratory culture 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 25.11 Figure 25.13A Table 28-3 Streptococcus pyogenes M protein Bordetella pertussis Pertactin Figure 25.14 Bacteria can attach to surfaces in bulk, forming a biofilm. - Play important roles in chronic infections Figure 25.15A 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. A subunit: Has toxic activity - ADPribosyltransferase - Diphtheria toxin - Cholera toxin Figure 25.17B Figure 25.17A Figure 13.7A Figure 25.20 ADP-Ribosylating Toxins • Animation: Cholera Toxin Mode of Action Click box to launch animation 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. • system - Blocks immune 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