Unit 1 - Determinants of Pathogenicity Flashcards
Define Pathogen
Organisms that cause disease in their host
What are 4 examples of pathogens?
- Multicellular parasites
- Single celled parasites
- Bacteria
- Viruses
True or False:
We rely on microbes to protect us everyday
True
- they create a biofilm on our skin
Define vertical transmission
Transmission of infectious disease from mother to embryo, fetus or baby during pregnancy or childbirth
Define horizontal transmission
Transmission of infectious disease after birth or from another source
True or False:
Transmission of infectious disease can be by direct contact or indirect
True
What is a vehicle?
A NON-living medium that can spread disease (water)
What is a vector?
A LIVING medium that can spread disease (mosquito)
True or False:
Vectors TEND to be indirect transmission
Vehicles TEND to be direct transmission
False
- Vectors tend to be direct
- Vehicles tend to be indirect
True or False:
Animal feces are vehicles, not vectors
True
- this is b/c animal feces are not living things
- they are an animal product
True or False:
The uterus is always germ-free
False
- uterus is germ-free until birth
What protects the uterus from vaginal microbes?
Fetal membrane
When does a baby first come into contact with microbes?
During delivery
When does colonization (of microbes) of a baby occur?
Within 8 - 12 hours after birth
What bacteria is contained within mother’s milk (when breastfeeding)?
Bifidobacterium (primarily)
- this bacteria has adapted along with us
True or False:
Bottle fed babies are exposed to more bacteria in bottled milk compared to breast fed babies in mother’s milk
True
- bottle fed = coliforms, lactobacilli, enteric streptococci, staphylococci
- breast fed = bifidobacterium
What percentage of microbes make up the human body?
90%
Define niche
A compartment with unique properties
temperature, pH, nutrients, etc
What are some examples of tissues that harbour resident microbes?
- skin
- upper respiratory tract
- GI tract
- vagina
- Urethra (outer opening only)
- External ear and canal
What are some example of tissues/organs that are germ-free?
- Brain
- Muscles
- Blood
- Lower respiratory tract
- Kidneys and bladder
- Bones
- Ovaries/testes
What is mutualism?
Two organisms cooperate to BOTH benefit
What is commensalim?
One organism benefits WITHOUT harm to the other
What is parasitism?
One organism benefits WHILE harming the other (or at the expense of)
What is a reservoir?
The source of the disease/pathogen
- where the disease comes from or where the disease is hiding
Why do we NOT want everything to be sterile?
Because if we get exposed to bacteria/pathogens
- we won’t have “good” bacteria to protect us
- not all microbes are bad
What must pathogens do first before they can infect an individual?
Adhere
- attach to the host
True or False:
Communal microbes have adapted to penetrate follicular canals on the skin
True
True or False:
After hand washing communal microbes will grow back
True
- because they have adapted to living in the follicular canals on the skin
What happens to communal microbes on the skin if you use anti-microbial soaps or alcohols?
They are all killed
- you then leave it up to chance with what you are colonized with next (whatever is in the environment)
Why is the epidermis part of the immune system?
Because it acts as a barrier
- skin is constantly falling off, and taking pathogens with it
Where do transient (temporary) microbes reside?
Colonize on the epidermis (surface)
Where do resident microbes reside (in relation to the skin)?
Penetrate into the deeper layers of the epidermis
What does it mean for microbes to be endogenous?
They are “within” the body
What does it mean for microbes to be exogenous?
They are “from an outside source”
What do sight, respiration, digestions, glandular secretion, birth, and urination - all have in common?
All require temporary exposure of internal tissues
Despite the hostile condition of the GI tract, why is it commonly colonized with microbes?
It is RICH in nutrients!
Approximately how many species makes up the biofilm of the mouth?
More than 600 bacterial species
What percentage of fecal volume do microbes make up?
Approx 10 - 30% volume
What does information the coliform count tell us?
Indicator of unsanitary conditions
Which bacteria in the large intestine provide vitamins to us?
E. coli
- they ferment waste and produce B12 and Thiamine
True or False:
The upper respiratory tract is germ-free
False
- the upper resp is rich in microbes
- the lower resp is germ-free
What is the suspected function of the tonsils and the appendix?
Sites where microbes are cultured
- grown on purpose and released when necessary
Describe what microbial antagonism is
Resident microbes protect against other potentially harmful pathogens
What is the female vagina usually inhabited with and why?
Lactobacillus
- when they eat the glycogen produced by the estrogen, it produces an acidic environment (pH 4.5) that prevents the growth of other microbes
What happens to the Lactobacillus in the female vagina if the patient takes a broad spectrum antibiotic?
Kills off good and bad bacteria
True or False:
Humans have been infected by retroviruses throughout our evolution
True
What is a distinctive feature of retroviruses?
Have the ability to integrate their DNA INTO the human (or other) genome
- virus DNA becomes part of the human genome
What happens to retroviruses once they integrate into your genome?
They become attenuated (less pathogenic)
- b/c they don’t want to kill you, they want the host alive
What retrovirus makes up 8 - 10% of the human genome?
HERV
- human endogenous retrovirus
Define biofilm
Multiple species of microbes grow together and cooperate
Define microbial antagonism
Good bacteria impairing the colonization of pathogens
What are probiotics?
Commensal organisms believed to support human health
What do broad-spectrum antibiotics do?
Kill off “good” and “bad” microbes
How do exogenous microbes enter the body?
Through portals of entry
Define infection
Invasion of microbes into germ-free tissue
What is the virulence factor?
A characteristic of a microbe that increases its capacity to cause HARM
What are the 7 steps of the infection process?
- Portal of entry
- Adhesion
- Invasion
- Multiplication
- Infection of target
- Disease
- Portal of exit
What does it mean if a pathogen has “infectivity” characteristics?
Capacity to invade and replicate in host tissue
If a microbe is pathogenic, how could you describe its virulence?
A quantitative measure of the pathology that results from infection
What is the infectious dose (ID)?
Minimum number of microbes to cause infection (morbidity)
What is the lethal dose (LD)?
Minimum number of microbes to cause death (mortality)
True or False:
A toxin can cause infection
False
- a toxin can be lethal, but they do not infect you
Define prevalence
Number of people in a population that are infected
Define incidence
Number of new cases (new infections) in a population
What does ID50 mean?
Minimum number of microbes to cause infection in 50% of the population
What does LD50 mean?
Minimum number of microbes to cause death in 50% of the population
True or False:
A microbe with a HIGH LD is more deadly than a microbe with a LOW LD
False
- a high LD means that you need a large number of the microbe in order to cause death
- a low LD means that you need very few microbes in order to cause death
Where is E. coli typically found?
In the lower intestine of warm-blooded animals
- produces toxins that break down the gut lining
Where is Vibrio Cholera found and what does it do?
Found in the small intestine of people and some aquatic habitats
- produces cholera toxin: draws salts and water into the intestion
- results in severe diarrhea
Should we be more concerned if a microbe has a HIGH ID50 and a HIGH LD50 … or a LOW ID50 and a LOW LD50?
LOW
- requires SMALL numbers in order to infect or kill
What does it mean if a pathogen is a “true” pathogen?
They can cause disease in individuals with a NORMAL functioning immune system
What does it mean if a pathogen is an “opportunistic” pathogen?
They only cause disease in immuno-compromised individuals
True or False:
E. coli are typically high infectious but have a low-moderate virulence
True
- ID50 = 10
- low to moderate virulence depending on the strain
True or False:
Vibrio cholera are typically highly infections and highly virulent
False
- poorly infectious (ID50 = 10^6 - 10^11
- but highly virulent!
What are three things that a pathogen must do in order to be virulent?
- Adhesion
- Invade - invade germ-free tissues/organs
- Immune evasion - overcome the immune system
What are some adapted measures that multicellular parasites have adapted to assist with adhesion (3)?
- Suckers
- Hooks
- Barbs
The head of a tapeworm has a crown of hooks, followed by a row of suckers to adhere to host’s tissues. Is this a specific or non-specific adhesion method?
Non-specific
True or False:
Tapeworms do not have their own digestive system
True
- they absorb nutrients from you!
What can the falgellum be used for, and is it specific or non-specific?
- Motility
- Adherence
- Non-specific
What can fimbriae be used for, and are they specific or non-specific?
- Motility
- Adherence
- Non-specific
What is a slime layer used for and is it specific or non-specific?
- Adherence
- Non-specific
Do gram (+) or gram (-) bacteria have a cell wall?
Gram (+)!
What is the primary component of the cell wall of gram (+) bacteria?
Peptidoglycan
thick layer
What is the main component on the outside of a gram (-) bacteria?
Lipopolysaccharide
- with a thin layer of peptidoglycan
What is the name of the layer of polysaccharide that can be sticky or form a protective coat around a bacteria?
Capsule
- has a sticky, sugary coating (non-specific)
What are the two main components of a virus?
- Capsid
2. Envelope
What is the role of the capsid in a virus?
It is the inner core where genetic material is contained (DNA or RNA)
What is the role of the envelope in a virus?
It is the outer membrane where specific virus proteins bind to very specific host proteins
What is the name of the viral protein on the outside of HIV that binds to the surface of human cells?
GP120
What is the relevance of HIV and influenza having RNA genome?
RNA mutates faster than DNA genomes
- easier for mutations to occur
What three non-specific features do multicellular parasites use for adhesion?
- Hooks
- Suckers
- Barbs
What three non-specific features do bacteria use for adhesion?
- Fimbriae
- Flagella
- Capsule
What two specific features do viruses use for adhesion?
- Envelope
2. Capsid
What are the three methods that pathogens can used to invade germ-free tissues?
- Exoenzymes
- Toxins
- Surviving endocytosis
True or False:
The human respiratory and digestive systems are vulnerable to invasion because the tissues are thin and in close proximity to the bloodstream
True
If fungi do not have a digestive system, how do they feed?
Secrete enzymes into the environment
- then absorb those nutrients
What are exoenzymes?
Enzymes that are secreted out of the cell
What is hyaluronidase?
A “spreading factor”
- breaks apart the “cement” that is holding your cells together
- your cells will fall apart from each other - resulting in open wounds
What does the suffix “-ase” indicate?
An exoenzyme
What does mucinase do?
Disrupts the protective mucous membranes
- an exoenzyme
What does keratinase do?
Digests structural proteins of skin and hair
- an exoenzyme
What does collagenase do?
Digests connective tissue
- an exoenzyme
What does hyaluronidase do?
Digests hyaluronic acid (cement that holds cells together)
- an exoenzyme
What does coagulase do?
Promotes blood clotting
- an exoenzyme
Why would some fungi have adapted to forming blood clots around them using coagulase?
If the fungi are surrounded by blood clots, the immune system won’t be able to find them
What kind of toxins are typically used in invasion?
Exotoxins
- used to kill any cells that are acting as a barrier
What do E. coli produce that kill gut epithelia?
Shiga toxin (verotoxin)
How have Salmonella enterica adapted to invade tissues?
Surviving Endocytosis
- Adhesion by fimbriae
- Secretion system (injects proteins into cells, reprogram them, tell them to eat Salmonella)
- Salmonella do not get eaten by lysosomes
- Multiply internally
- Released into bloodstream in large numbers
What are 4 things that pathogens would have to evade in order to survive the immune system?
- Tissue barriers (physical barriers)
- Gastric juices (physiological barrier)
- Anti-phagocytic factors
- Leukocytes
What is the name of the microbe that lives in the stomach of approx. 50% of people?
Helicobacter pylori (H. pylori)
How have H. pylori adapted to living in the stomach of people (2)?
- Corkscrew motion of flagella drills the microbe through mucosal lining of the stomach
- Produces urease enzyme which degrades urea into ammonia … this neutralizes the stomach acid
How can a microbe survive phagocytosis (2)?
- By creating a capsule to surround it
2. Hiding inside host cells
What are leucocidins?
Toxins secreted by some microbes that specifically kill immune cells
- it is a protein
What is the resulting effect of leucocidins?
Will immuno-compromised the host
What are two examples of microbes that secrete leucocidins?
- M. tuberculosis
2. HIV
What does the suffix “-in” tell you?
It is a PROTEIN!
What are the two classes of toxins?
- Endotoxin
2. Exotoxin
What kind of bacteria produces endotoxins?
Produced by gram (-) bacteria
- from degradation of lipopolysaccharide cell wall
When are endotoxins fatal?
Only fatal in LARGE doses
- can induce fever that can lead to death
What kind of bacteria produces exotoxins?
Produced by gram (-) OR gram (+) bacteria!
True or False:
Exotoxins are proteins
True
When are exotoxins fatal?
In SMALL doses
- can lead to tissue or organ failure
True or False: A gram (+) bacteria can produce endotoxins and exotoxins
False!
- A gram (-) bacteria can produce endotoxins and/or exotoxins
True or False:
If you heat up an endotoxin, it will degrade
False
- Endotoxins are stable at high temperatures b/c they are lipids
- therefore, still toxic when heated
True of False:
Endotoxins cannot be converted to toxoids
True
- antibodies do not bind to lipids well - therefore there is NO ANTI-TOXIN
What is the main clinical concern when dealing with endotoxins?
Managing the escalation of the inflammatory response
What is a toxoid?
A modified toxin
- it keeps its general shape, but it is not as harmful
- we can make antibodies against them
True or False:
Exotoxins denature at high temperatures
True
True or False:
Anti-toxins cannot be produced for exotoxins
False
True or False:
Exotoxins are the result of the degradation of the lipopolysaccharide cell wall
False
- Exotoxins are secreted from LIVE cells
True or False:
Endotoxins can cause damage if the cells are alive or dead
True
- this is because the toxins are released from the degradation of the LPS
What is an example of a Receptor Ligand Exotoxin?
AB toxin
- Pertussis
- Cholera
- Shiga
What are two domains of the AB toxin and what do they do?
A domain = an enzyme that disrupts the cell function
B domain = binds to a specific receptor on the target cell surface
True or False:
AB toxins enter the target cell via endocytosis
True
What happens to the AB toxin once it enters the target cell?
Lysosomes break up the AB linkages
- A domain gets released into the body and causes harm
- (acidification of vacuole dissociates th A enzyme)
True or False:
Endotoxins can be deactivated and then injected into a host to make antibodies
False
- EXOTOXINS can be deactivated and then injected into a host to make antibodies
What happens when a patient is injected with a toxoid?
Patient becomes immune to the toxin
- these are exotoxins
What happens when a patient is injected with an anti-toxin?
Rapid relief to a NON-IMMUNE patient
- immunity is NOT transferred
- these are exotoxins
What are two examples of exotoxins that affect the GI tract? What is their proper name and what do they do?
Enterotoxins
1. Shiga toxin = E. coli degrades the GI wall = blood diarrhea
- Choleragen (produced by Vibrio cholera) - stimulates water secretion into gut = rice-water stool
What is the botulism toxin an example of and what does it do?
Botulism toxin = Neurotoxin
- causes flaccid paralysis (numbness)
What is tetanus an example of and what does it do?
Tetanus = Neurotoxin
- causes spastic paralysis (constant muscle contraction)
What is the name of the exotoxin that affects red blood cells? What does it do?
Hemolysins
- S. pyogenes
- breaks open RBCs
What is the name of the exotoxin that affects white blood cells? What does it do?
Leucocidins
- S. aureus (necrotizing pneumonia)
- Targets WBCs and destroys them
Which has a lower LD50, endotoxins or exotoxins?
Exotoxins
- you only need a small amount to kill someone
True or False:
Exotoxins are proteins
True
What are 4 types of exotoxins?
- Enterotoxin = GI
- Neurotoxin = neurons
- Hemolysin = RBCs
- Leucocydin = WBCs
What is the role of hemoproteins in humans?
Helps iron dissolve by associating it with proteins called hemoproteins
- ferratin, transferrin, lactoferrin
True or False:
Bacteria, fungi and other microbes have easy access to iron
False
- they are often starved for iron
- therefore, adapted proteins that bind iron at HIGH AFFINITY
What is affinity?
The strength at which two molecules bind
What are siderophores and what do they do?
High-affinity proteins that absorb heme and iron
- to be taken back into the cell
What microbes secretes siderophores?
Bacteria
- TB, E. coli, Anthrax, Cholera, Black Plague
What is the suffix that indicates a siderophore?
“-bactin”
In the body, what are a rich source of iron?
RBCs
What can microbes produce that disrupt RBCs in order to access their iron content?
Hemolysin
What is one method of classifying Streptococcus species?
By their hemolysis patterns
What is the important difference that a chocolate agar and a blood agar plate will tell you?
- If it grows on chocolate, it likes iron but cannot lyse RBCs
- If it grows on blood agar, it likes irons AND can lyse RBCs
What does the alpha pattern tell you?
Partial lysis of RBCs
- ex: S. pneumoniae
What does the beta pattern tell you?
Complete lysis of RBCs
- ex: S. pyogenes
What does the gamma pattern tell you?
Non-hemolytic
- non-pathogenic commensals
True or False:
Humans bind iron to siderophores while bacteria bind iron to hemoproteins
False
- Humans bind iron to hemoproteins
- Bacteria bind iron to siderophores
True or False:
Mechanisms involved in evolution and adaptation are considered virulence factors for microbial populations
True
The immune system uses what two key antigens to identify and develop immunity against influenza?
- Hemagglutinin (HA)
2. Neuraminidase (NA)
What does the virus do if the immune system detects a specific HA antigen shape?
The virus mutates to change it’s shape
What is “antigenic drift”?
Small changes/variations
- DUE TO MUTATION
- changes are small enough that it will cause symptoms but your immune system will recognize the virus
What is “antigenic shift”?
Major changes
- DUE TO GENETIC REASSORTMENT
- so much so, that your immune system does not recognize it as the flu (example)
- immune system does not formulate a response
True or False:
Avian flus rarely infect humans. But avian and human influenza can infect pigs
True
What happens TO THE VIRUS if a pig is infected with both avian and human influenza?
The virus reshuffles its RNA molecules
- to form a virus that is dramatically different
- we would not have immunity to it
What is genetic reassortment?
When a virus reshuffles it’s RNA (or other genetic molecules)
- ex: avian and human flu in pigs = new flu virus
What does antigenic drift usually cause?
A disease outbreak
- a disease that occurs at greater frequency
What does antigenic shift usually cause?
A pandemic
- humans have no natural immunity and the disease quickly spreads throughout the world
What is the african sleeping sickness caused by?
Protest parasite called a TRYPANOSOME
Why is it so hard for the immune system to beat the african sleeping sickness?
It has VARIABLE surface glycoproteins
- once the immune system develops resistance
- the pathogen changes shape to evade the immune cells
What is antigenic variation?
Changes in cell surface features to evade immune cells
