INFECTION AND IMMUNITY Flashcards
Residents within an on surfaces of
human host
Mostly of “symbiotic relationship
But they can become opportunistic
normal microbiota
what is opportunistic infection
Infections that take advantage of weakness in immune defenses
when do normal microbiota become opportunistic
Their habitat is altered
Compromised host immune system
role of microbiota in host defense
Helps develop immunologic competence since they primed the immune system during contact
– inhibit closely related pathogenic
bacteria
bacteriocins
Refers to the ability of the organism to produce
disease in an individual
pathogenicity
difference of true pathogen and opportunistic pathogen
A true pathogen is an infectious agent that causes disease in virtually any susceptible host. Opportunistic pathogens are potentially infectious agents that rarely cause disease in individuals with healthy immune systems.
Results from medical treatment or procedures
Iatrogenic infection
Considerations to note when deciding if an isolate is a pathogen or just a contaminant
▪ Presence of underlying conditions
▪ Age
▪ Persons receiving transplant or immunosuppressive
therapy (i.e chemotherapy)
▪ Presence of immunosuppressive disease (AIDS)
What is the route of transmission where secretions are aerosolized by coughing, sneezing, and
talking
airborne
What is the route of transmission where there is physical contact
direct contact
What is the route of transmission where you touch objects, ate contaminated food or water, or got bitten by vectors
indirect contact
Differentiate VERTICAL from HORIZONTAL TRANSMISSION
In horizontal transmission, viruses are transmitted among individuals of the same generation, while vertical transmission occurs from mothers to their offspring.
Define PARENTERAL TRANSMISSION
Parenteral transmission is defined as that which occurs outside of the alimentary tract, such as in subcutaneous, intravenous, intramuscular, and intrasternal injections.
Relative ability to cause disease or the
degree of pathogenicity. Influence by:
▪ Infectious dose
▪ Virulence factors
Virulence
What are avirulent organisms?
An avirulent disease or organism is not, or is no longer, dangerous, and does not spread
WHAT VIRULENCE FACTOR?
- Presence of bacterial capsules
- Interference by Protein A of staphylococci
- Release of leukoctoxic substances
▪ Haemolysins
▪ Leukocidins (PVL)
Phagocyte evasion
WHAT VIRULENCE FACTOR?
▪ Main adhesins in bacteria
▪ Once attached, they can resist phagocytosis and can release toxins
Adhesion to host cells
WHAT VIRULENCE FACTOR?
- Host factors that prevent proliferation
- THIS CAN LEAD TO INVASION OR WORSE, DISSEMINATION
Intracellular survival and proliferation
WHAT VIRULENCE FACTOR?
- Release of exotoxins and enzymes
- Poisonous substances that interact with host cells, disrupting
normal metabolism
- Produced by both gram + & - bacteria
- Released via secretion or after lysis of the bacterial cell
- Release of endotoxin
- Constituent of the of the LPS of gram negative
bacteria
- It does not have enzymatic activity
- Secreted in small amounts! ☺
- Released in LARGE AMOUNTS when bacterial
cell lyses
Production of extracellular enzymes and toxins
activates the fever center of the hypothalamus
Interleukin 1
vasodilator and chemo attractant
Tumour Necrosis Factor
vasodilator
Histamine
Interaction of “sentinel” cells with microorganisms
activate them and caused them to secrete
proinflammatory cytokines
Inflammation
The dilated blood vessels allow the leakage of
plasma components into the tissue which
include:
▪ Red blood cells
▪ Platelets
▪ White blood cells
▪ Enzymes and other substances
▪ Plasma
Effects of endotoxin
▪ Prolonged inflammation and fever
▪ Hypotension
▪ Septic shock
▪ Intravascular coagulation
▪ Severe bleeding
In large amounts, it can stimulate production of “proinflammatory” cytokines
endotoxin and inflammation
antimicrobial sections in the physical barrier
Fatty acids in the skin
Stomach acidity
IgA in secretions
Lysozyme
Beta lysin
Interferon
hydrolyses peptidoglycan of gram
positive bacteria
Lysozyme
released by platelets which are lethal to
gram positive bacteria
Beta lysin
inhibits proliferation of viruses
Interferon
Migration of neutrophils to the site of injury
▪ Movement from area of low concentration gradient to high concentration gradient of chemo attractants
Phagocytosis: chemotaxis
Direct physical contact is mediated by:
Pathogen Associated Molecular Patterns
Pattern Recognition Receptors
indirect physical contact is mediated by:
opsonins
Phagocyte’s membrane invaginates and surrounds the microorganism
Engulfed microorganism is transported into the cytoplasm and is enclosed in a vacuole called “phagosome”
Phagosome fuses with the lysosomes forming
“phagolysosome”
Lysosomes release lysosomal enzymes which digest the microorganism
phagocytosis: ingestion
Increase oxygen consumption resulting to the production of toxic O2 metabolites such as:
▪ O2- (superoxide anion)
▪ H202 (hydrogen peroxide)
▪ HClO (hypochlorous acid)
What stage of infection: No signs or symptoms
Incubation stage
What stage of infection:- First signs and symptoms, pathogen may be highly communicable
Prodromal stage
What stage of infection:- Peak of characteristic signs and symptoms of infection or disease
Period of illness
What stage of infection: Condition of host deteriorates possibly to death or signs and symptoms begin to subside
Stage of decline
What stage of infection: Full recovery of surviving host or chronic infection develops, or death
Convalescent stage
