Bac/fungi Pathogenesis Flashcards
Facultative intracellular
Can reproduce within and outside of host cell
Salmonella, Neisseria, Brucella, Mycobacterium, Listeria Francisella, Legionella, Yersinia Petis
(see first aid pneumonic)
Obligate Intracellular
Can’t make own ATP
Can’t reproduce outside of host cell
Rickettsia
Chlamydia
STEPS OF THE PATHOGENIC CYCLE
Exposure & Entry Attachment Invasion Evasion of immune response Effects on host Dissemination/Shedding
Attachment
Requires host cell receptors & microbial surface components (Adhesins such as pili/fimbriae, LPS, Lipoteichoic Acid, Mannans)
Invasion
Ex: Phagocytosis, endocytosis, cytoskeleton rearrangement (membrane ruffling)
Evasion of immune response
Ex)
Compliment evasion = capsules, host cell mimicry, compliment binding proteins, proteases (elastase, C5a peptidase)
Phagocyte evasion = capsules, intracellular parasitism
Antibody evasion = Ig binding/inactivating, antigenic variation
Leukocidins
Kills neutrophils and macrophages
Alters phospholipid metabolism by ADP-ribosylation of a protein controlling phosphatidylinositol = disruption of cellular activities
Biofilms
Collection of microorganisms that are attached to a surface, covered by a microbially-produced exopolymeric substance (EPS)
Bacteria growing as biofilms can be SIGNIFICANTLY more resistant to antimicrobial agents
Effect on Host
- Degradative Enzymes (kinases) result in spreading to other tissues
- Physical growth through tissues: Fungal growth
- Toxic Structures: Lipid A/LPS/Endotoxin
- Toxins: exotoxins (-ve), aflatoxin (fungi, carcinogenic), Gliotoxin (fungi, induces apoptosis)
Classes of Exotoxins
Class I: membrane binding/acting
Class II: membrane damaging
Class III: Interacellular
Superantigens
cause non-specific activation of T-cells resulting in polyclonal T cell activation and massive cytokine release (INF-gamma, IL-2)
Ex: toxic shock syndrome (staph), Rheumatic fever (strep)
Dissemination
a) Direct: In surface fluids
- Facilitated by toxin production (Ex: hyaluronidase, etc.)
- Growth through tissues, (fungi)
b) Cross blood-CSF junction (choroid plexus)
c) Blood or blood components
d) Lymphatics/ immune system cells