pathogenesis

Fig. 1-15KOCH’S POSTULATES

Tools:Diseasedanimal

Healthyanimal

Redbloodcell

Observeblood/tissueunder themicroscope

Redbloodcell

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.

Suspectedpathogen

Microscopy, staining

Noorganismspresent

Streak agar platewith sample from eitherdiseased orhealthy animalColonies of

suspectedpathogen

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 withcells of suspected pathogen

Remove blood or tissue sampleand observe by microscopy

Laboratoryculture

Suspectedpathogen

Laboratory reisolation4. The organism should be reisolated and shown to be the same as the original.

Pure culture(must besameorganismas 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

Figure 25.14Figure 25.14

Bacteria can attach to surfaces in bulk, forming a biofilm.- Play important roles in chronic infections Figure 25.15A

Streptococcus pyogenes M proteinBordetella 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