Bacterial Pathogenesis and Host Defences - Sheet1-1 Flashcards
hypersensitivity
refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity.
endotoxin is only produced by _______
gram neg bacteria
Pathogen
bacteria capable of causing disease
Virulence
quantitative measure of pathogenicities measured by the number of bacteria required to cause disease
LD50
number of bacteria necessary to kill half the host
ID50
number of bacteria necessary to cause infection in half the hosts
Virulence Factors
properties of a bacteria which assist in causing disease ex: pili, capsules,
Bacterial Structure virulance factors
Pili, Capsules Glycocalyx Endotoxin Biofilms Bacterial Secretion Systems
Coagulase
eg. Helps coat Staph. aureus with fibrin to help protect from phagocytosis
Immunoglobulin A protease
Degrades IgA allowing Strep. Pneumonia to adhere to mucous membranes
Leukocidins
a type of cytotoxin created by some types of bacteria. It is a type of pore forming toxin. Leukocidins get their names by killing (“-cide”) leukocytes
Other Bacterial Factors
M protein - antiphagocytic protein produced by Strep. pyogenes
Protein A - binds to IgG and prevents activation of complement
Invasins - bacterial molecules which promote bacterial entry or contact with host cells - eg. Heliobacter pylori
Outer membrane proteins - produced by Yersinia species to inhibit phagocytosis and cytokine production
**Pathogenicity Islands (PAIs) – code for groups of virulence factors particularly in **Gram negatives
Pathogenicity Islands (PAIs)
code for groups of virulence factors particularly in **Gram negatives. Some are located on chromosomes and some are not.
Exotoxins
Polypeptides secreted by bacteria
Become toxoids when treated with formaldehyde, and/or heat and used for protective vaccines
Frequently have an A-B subunit structure (A portion has toxic activity and B portion is involved in binding to cells)
Are genetically coded on the bacterial chromosome, plasmid or phage
Have one of five biological effects:
- -Alter cellular components
- -Are superantigens
- -Inhibit protein synthesis
- -Increase synthesis of cAMP
- -Alter nerve impulse transmissions
Endotoxins
Are integral parts of the cell wall of Gram negative rods and cocci
Involve the Lipid A component of lipopolysaccharide
Only weakly antigenic; no toxoids made
Induced biological effects focus on fever and shock
two types of immunity
1. Innate Immunity Macrophages ---Phagocytize and digest bacteria Complement ----Assist host immune cells and antibody in lysis of bacteria and virus-infected cells
2. Acquired Immunity Antibodies ---Cytolytic ---Neutralizing: body synthesizes ***antibody to viral receptor protein. Ability of virus to infect is lost ---Opsonins
Cytotoxic T Cells: recognize antibody binding and kill bacteria
—Kill antibody-coated bacteria and virus-infected cells
Passive vs. Active Immunity
Passive Immunity
- –Administration of preformed antigen-specific antibodies to help protect from disease ex. Human rabies immune globulin Active Immunity
- –Administration of specific antigens to stimulate an individual to develop immunity to help protect from a disease ex. Influenza vaccine
Avoiding the Innate Immune Response–avoid their killing by macrophage
There are essentially three categories of bacterial strategies to deal with phagocytic cells:
- Avoiding contact with phagocytes
- Inhibition of engulfment
- Survival within the phagocyte
Stapholoccocal virulance factor:
*Protein A: binds immunoglobulin (IgA)–which disguises itself from immune response.
Pseudomonas aeruginosa
An opportunistic pathogen that infects humans with compromised natural defences. The propensity of P. aeruginosa to form biofilms further protects it from antibiotics and from the host immune system.
influenza
Orthomyxoviruses. Enveloped, negative single stranded RNA viruses with 8-segment genome. Contain hemagglutinin (promotes viral
entry) and neuraminidase (promotes progeny virion release) antigens. Patients at risk for
fatal bacterial superinfection. Rapid genetic changes.
Corynebaderium
diphtheriae
Causes diphtheria via exotoxin encoded by beta-prophage. Potent exotoxin inhibits protein synthesis via ADP-ribosylation ofEF-2.
Symptoms include pseudomembranous pharyngitis (grayish-white membrane) with lymphadenopathy, myocarditis, and arrhythmias.
Lab diagnosis based on gram-positive rods with metachromatic (blue and reel) granules and Elek’s test for toxin.
Toxoid vaccine prevents diphtheria.
