MMI 301-Exam 2-Lecture 8: Microbes as Pathogens

Bacteria that already live in body, protect from colonization, provide nutrition and stimulate immune system

Virulent Bacteria that commonly cause disease

Bacteria that will cause disease w/ pre-existing conditions

Rapid Onset, Rapid resolution  (cholera)

Slow onset, slow resolution (tuberculosis)

Multiple acute bouts (UT E. Coli)

Causes fever, white cell infiltration and pus (Staph/Strep wounds)

Antibody/Cellular response to organism damaged tissues (rheumatic fever)

Salmonella,Shigella, Vibrio cholerae, Listeria, Bacillus anthracis

Mycobacterium tuberculosis, Legionella pneumophila, Bordetella, B. anthracis, Staphylococcus

• Clostridia tetani, B. anthracis,
• Staphylococcus

Rickettsia,Yersinia pestis, Borrelia sp.

Chlamydia trachomatis, Haemophilus ducreyi, Treponema pallidum, Neisseria gonorrhoeae

T.pallidum, Listeria monocytogenes

C.trachomatis, N. gonorrhoeae, Pseudomonas, Haemophilus influenzae

• Adhesion
• Cellular Invasion
• Exotoxins
• Endotoxins
• Superantigens
• Capsules
• Evasion of Immune Defenses
• Iron Acquisition
• Disruption of cell signalling
• Motility

• should be associated with pathogenic members of a genus
• -Specific mutagenesis of gene(s)
• associated with the suspected virulence factors should show a measurable loss
• of virulence in an appropriate model system. (In-frame/point mutation best)
• -Complementation of mutatation by
• recombinant plasmid or allelic replacement with wild type should lead to
• restoration of pathogenicity

• -Pili/fimbriae:attach to host or other bacteria
• -Non-fimbrial surface proteins
• -Capsule
• -Lipoteichoic acids
• -Flagella

• -Bacteria bind cell surface
• -Induce engulfment into a phagosome
• -Normally phagosome acidified and it fuses with lysozyme, kill bacteria
•          -Uses destructive enzymes and oxide   radicals

• -Invasion with replication in cytoplasm (Rickettsiae/Shigella/Listeria)
• -Invasion with replication in late endosomes (Salmonella)
• -Invasion with replication in phagolysosomes (Coxiella/Mycobacteria)
• -Special parasite vesicle: inclusion bodies of Chlamydia sp.

• -Some intracellulars can do this without ever being in extracellular environment
• -Shigella/Listeria
• -Enter host cells
• -Rapidly lyse phagosome
• -Replicate and organize polymerization of actin filaments
• -Use actin to propel themselves into neighboring cells
• -Lyse double membrane surrounding them
• -Repeat

• -Usually function as two discrete proteins subunits/two units of same protein
• -Ability to recognize/bind specific host cell receptors from one subunit
• -Toxic actions from other subunit
• -Discrete elements needed for secretion from bacterial cell
• -Also need parts for translocation across plasma membrane of host cells
• -This depends on mode of entry

• -Creation of membrane pore
•        -alpha toxin of Staph. Aureus
• -Enzymatic destruction of phospholipid bilyar
•        -alpha phospholipase C of Clostridium perfringens
• -Surfactant
•        -delta toxin of S. aureus

• -Some Gram –
• -Directly deliver bacterial proteins into host cell cytoplasm
• -Proteins can affect a variety of different host cell functions
•        -Cytoskeletal structure
•        -Structure of messenger pathways
• -Needle like structure, injects
• -Helps E. coli make actin pedestals

• Type V/II: Sec-dependent
• Typer I/III/IV: Sec-independent