Session 7: Pathogenicity Flashcards
Opportunistic pathogens
A microorganism that may cause disease if given right circumstances
Primary pathogens
Cause diseases in healthy immunocompetent individuals.
Virulence
A measure of the amount to which the microorganism is pathogenic
Virulence factor
Something that helps the virus (ex: a capsule)
Portal of entry
Chlamydia and mucous membrane
Salmonella and GI system
Tropism (type of cell they infect)
Influenza virus and respiratory epithelium with sialic acid
E. coli and urinary tract epithelium with D mannuse residues
Microbes that produce toxins that get into cells
Corynebacterium diphtheriae ( icky membrane in the back of throat and suck down into lungs)
Cholerae, pertussis
Skin as portal of entry
One of the largest organs in body (SA)
- few organism can breach the intact skin (hookworms)
- most organisms need a break in skin to enter (S. Pyogenes-flesh eating)
- some bacteria enter through sweat and hair follicles and skin (scenes and aureus)
Adherence
1st step towards establishment of infection, organism gets a foothold
- penetration of cell walls/membranes occurs
- facilitated by adhesions or ligands and receptor that bind and recognize structures.
- include lipoprotein and glycoproteins
N. Gonorrhoae
Pilli or fimbriae contain adhesions
S. Mutons
Glycocalyx
Capsules
Glycocalyx- presents C3b from binding and the phagocyte from recognizing and ingesting the Bacteria. Also aids in adherence to host cells. Antibiotics produced in the capsule enables phagocytes to ingest organism.
Ex: pneumonioe, ecoli, gonorrhoea
M. Protein: streptococcus pyogenes
Heat and acid resistant protein in cell wall that allows attachment of bacteria to epithelial cells and inhibits phagocytosis
Mycolic acids
Tuberculosis
-waxy substance in cell walls make the bacterium resistant to digestion, inside the phagocyte
Fc receptors
With Fc receptors in cell wall, then it binds the Fc area of the antibody
-prevents macrophages from biding due to the inability to bind to Fab area
Bacteria without Fc receptor in cell wall is….
Phagocytosis happens
Exoenyzmes
released from bacterial cells
- Leucocldin: destroys blood cells ( S. aureus)
- Kinase: break down fibrin and dissolve clots, forms by body to isolate infection
- Hemolysin: breaks down RBC (includes staph, strep, listeria)
Coagulase
clots; coverts fibrinogen (soluble) to fibrin ( insoluble). Clot can wall off from the host defenses: convert real protein strands that cause the clot
collagenase
breaks down collagen, connective tissues (clostridium)
Lecithinase
destroys plasma membranes
proteases
inactivates antibodies and other body proteins ( breaks down proteins), IgA
coagulase test
- take rabbit plasma ( contains all the blood clotting proteins that haven’t been activated yet) and bacteria
- incubate it
- Positive means clot, fibrin is solid (coagulase produced aureus)
Negative means no clot, no fibrin, liquid (epidermis)
other factors bacteria used to affect virulence
- Necrotizing factor: kill body cells (small chemicals)
- hypothermic factor: lowing temperature
- siderophores: scavenge and bind iron; bacteria needs iron to grow
superantigens: Type I toxins ( endotoxins)
- protein poisons that are made inside the cell and then exported to outside of cell
- protein antigen that stimulate a very large immune response
- they produce excess inflammation and cytokines, nausea, death, shock ( TSS)
- bind outside binding group, activate a lot more T cells than normal antigen binding
toxins
- often a primary virulence factor
- are usually proteins that produce fever, cause heart failure, edema, shock, diarrhea
- destroys cells as well as inhibit protein synthesis, leads to cell death
2 types:
- exotoxins: superantigens
- endotoxins: lipid A moiety
Endotoxins
- part of outer cell wall gram (-) bacteria LPS
- LPS= polysaccharide and lipid A ( endotoxin): heat stable
- chills, fever, weakness, aches, shock and death
- activates blood clotting system ( DIC)
- Shock: life threatening loss of blood pressure ( septic- bacteria caused, endotoxic is gram negative)
Exotoxins
- produced by certain types of bacteria and released into the tissue ( gram positive or negative)
- genes are carried on bacteriophages or plasmids
- proteins: 3 types ( cytotoxin, neurotoxin, enterotoxin)
- most are heat labile ( 5 min boil)
- body produce antibodies called antitoxins to neutralize endotoxins
Invasins
- surface proteins on some bacteria which activates actin ( cytoskeleton of cell)
- rearranges and allows bacterial penetration of the cell
- includes salmonella and E. coli
- some bacteria use their invasions to move from host cell to another host cell. These bacteria infect intestinal epithelia cells laterally and evade immune cells.
pathogenicity islands
- some bacteria, especially the gram negative have genes encoded on their chromosomes that code for pathogenic attributes.
- type III secretion apparatus enables a bacterial cell to inject proteins into a host cell, killing or altering it
Antigenic variation: “fooling immune system”
- pathogens have antigens on their surface to which B cells produce antibodies
- some antigens change the makeup of their antigens- creates a new pathogen
- Ex: neisseria gonorrhoeae: has Opa gene codes for surface antigens
- some organism can use host cell antigens to cover themselves and hide from host immune defenses
intracellular growth
- obligate intracellular bacteria: only grow inside of host cell; often in protected vacuole (can’t produce its own energy)
- ex: chlamydia, rickettsia
-facultative intracellular bacteria: bacteria that can multiply outside of host cells, but often use intracellular growth as means of evading host defenses ( replicate inside and outside the cells, like TB)
how do bacteria acquire new genes?
transfer of DNA between bacteria
- conjugation: mating of 2 cells with transfer of plasmid/chromosomal DNA
- transduction: transfer of DNA by a virus ( bacteriophage) from cell to cell
- transformation: purified DNA taken up by cell
plasmids
these are small circular DNA molecules separated from the main bacterial chromosome ( conjugation)
R factors
a group that is responsible for transferring the genes for antibiotic resistance
- may also encode for virulence factors, toxins, tetanus toxin, heat labile toxin of E. Coli
viral pathogenicity
- can inhibit macromolecular synthesis ( stop mitosis)
- can down regulate MHC I
- syncytium formation: some viruses like RSV host cells fuse together to form a giant multi-nucleated cell
- can deregulate cell function ( affect hormone production)
- induce chromosome changes in cells ( oncoviruses)
- down regulating P53 and RBio7, allow cell growth and tumour
syncytium formation
infected cells fuse to form a giant cell with many nuclei
- permits viral multiplication without exposing virus to antibodies
- leads to dead tissues
newborns contact with bacteria is….
lactobacilli from mother’s vagina
location of normal flora
- respiratory: streptococcus species ( mostly alpha hemolytic)
- GI: bacteroides fragillis
- Skin: S. epidermis
- Vagina: lactobacilli
transient microbiota
- microorganisms that may be present on body surfaces temporarily and then disappear
- removed by handwashing
- can be either pathogenic ( disease causing) or nonpathogenic
- doesn’t necessarily cause disease unless special conditions prevail
microbial antagonism
- where normal flora prevents overgrowth of harmful microorganisms
- involves competition for nutrients, cellular receptors, production of substances that affect pH and available oxygen
- if balance is upset, disease can result
symbiosis
relationship between host and normal flora
commensalism
one of the organism is benefited and other not affected
mutualism
benefits both organisms
parasitism
one organism is benefited, the other is not and is usually damaged by the parasite ( pathogen)
Zoohosis
- disease transmitted to humans from an animal
- animal may be healthy carrier or may be diseased, human is an accidental host
- includes rabies, west nile
stages of diseases
- incubation period: where it can start causing disease
- prodrome: feeling sick, scratchy throat, itchy
- illness: number of organism increase and plateau out since immune system kicks in
- death
- period of decline
- convalescence: getting better, but there are bacteria and viruses still hanging out around
iceberg of infection
- undetectable
- asymtomatic infection has no symptom, immune response occurs
horizontal transmission vs. vertical transmission
horizontal: transmission from one person to another through contact, ingestion, vectors etc. ( include chickenpox, strep throat)
vertical: transfer of a pathogen from a pregnant woman to her fetus ( include HIV from breastmilk)
contact transmission include
a. direct: person to person such as kissing and touching
b. indirect: agent transferred from reservoir to host by fomite
c. droplet: mucus droplet; sneezes
vehicle transmission
transmission of infection by a medium such as water, food, air, blood, IV fluids ( hep B and TB)
vectors transmission includes…
arthropods
a. mechanical: passive transport on vector’s body ( shigella)
b. biological: part of the life cycle of microorganism is in the arthropods body ( malaria)
epidemiology
study of where and when disease occur, the purpose is to control disease transmission
prevalence
number of diseases in the population at a particular point in time ( usually in percentage)
morbidity
incidence of specific diseases
mortality
number of deaths from disease
pandemic
disease occurring all over the world
What to do when faced with an HIV accident
- wast needle-sticks, cuts with soap and water
- flush splashes to the nose, mouth, skin with water
- irrigate eyes with clean water, saline, sterile irritants
- report incident
- immediately seek medicate attention
- HIV: antiviral therapy
- Hep B and A: immediate vaccination or immunoglobulin therapy
