Ch. 15 - Microbial Mechanisms of Pathogenicity Flashcards
Define: Pathogenicity
disease process; ability of pathogen to cause disease in host
Define: Virulence
enhanced ability of pathogen to cause infection (DZ in host)
Define: Virulence Factor
Provide examples
IMPORTANT TERM
characterisitc/trait of the pathogen that makes it harmful
- capsules, toxins, anitgenic variation (Ag changes it composition; viruses’ spikes)
Define: Mechanisms of Pathogenicity
the different ways a microbe can cause an infectious disease
Generally describe the Mechanisms of Pathogenicity regarding: adherence, penetration/evasion, damage to host, and exit
Pathogens enter via PORTALS OF ENTRY
- mucous membranes
-> respiratory tract, gastrointestinal, genitourinary, conjunctiva (eye) - skin (broken)
- parenteral route (passes GI ➜ goes to blood)
X# of invading pathogens adhere (attach) to tissue
Pathogens attempt to PENETRATE/EVADE HOST DEFENSES (immunity)
- Capsule
- CW components
- Enzymes
- Antigenic variations
Pathogens do DAMAGE TO HOST CELL
- toxins
-> Exotoxins, endotoxins
Pathogens usually leave the same way they entered via PORTAL OF EXIT
- mucous membranes
- skin
- parenteral route
Name the different Portals of Entry (how pathogens enter a host)
mucous membranes
skin (broken)
parenteral route
Describe the Parenteral Route and how it is achieved
Provide examples
IMPORTANT TERM
Parenternal Route
- non oral entry; pathogens directly deposited into tissue/bloodstream
- inv. “injection” into a blood vessel
-> ex: intravenous (IV) entry by contaminanted needle/insect bite
If the number of pathogens is _____ it can overwhelm host defenses and cause a infection and _____
high
disease
Define and Describe ID50
What is it “used” for
Infectious Dose 50
- the number of pathogens required to make 50% of the population sick
- measures virulence of a microbe
- indicates preferred portal of entry to cause disease (look for low ID50)
What is the relationship between ID50 and infectiousness?
infectious pathogens have different ID50s:
Pathogens with LOW ID50 = High infectiousness/very virulent
Pathogens with HIGH ID50 = Low infectiousness/less virulent
Which bacterium is responsible for anthrax? What is it?
What portal(s) of entry does it use to invade the the host? Understand the trend of ID50 of each portal.
Which is the preferred (“easiest”) route for developing Anthrax?
Bacillus Anthracis; is a spore-former
- Skin; broken (low ID50)
- Inhalation; lung
- Ingestion; GI tract (high ID50)
Preferred route: Broken skin, because a low ID50 means that a small number of bacteria is very virulent/highly infectious and will easily cause host to get sick.
Some bacteria produce ____ that can cause the _____ of the host (______)
toxins
death
(lethality)
Define and Describe LD50
What is it “used” for
Lethal Dose 50 (conc. of toxin)
- amount of toxins require to KILL 50% of population
- measures potency (strongness/poisoinous) of toxin
What is the relationship between LD50 and lethality and potency of a toxin
Toxigenic pathogens have different LD50
- Pathogens with low LD50 = high lethality/very potent/toxic
- Pathogens with high LD50 = low lethality/less potent/toxic
Two pathogens are compared in a table regarding their LD50.
Pathogen #1 (Abbys pedos) have an LD50 of 1000mg/kg
Pathogen #2 (Joshs pedos) have an LD50 of 2mg/kg
Which pathogen (or pedo) is more lethal? Explain why
Pathogen #2 (Joshs pedos), because it has a small LD50 value. A small LD50 value means that a small number of toxin is required to kill 50% of the population, indicating that it is very potent and highly lethal.
Define: Adherence (adhesion)
ability of pathogens to attach to host tissues/cells
Deinfe: Bacterial Adhesins (Ligands)
substances on the pathogen that bind to receptors on the HOST CELL
NOT AG DETERMINANTS! Although Ag Determinants are on the surface of an Ag, they bind to antibodies. Whereas, ligands bind to receptors of the host cell
List 5 examples of adherence factors (adhesins/ligands)
What is their general function?
structures that serve for attachment to host tissue
- Capsule (stickness allows it to bind to tooth)
- Fimbriae
- M proteins (in bact cw)
- Opa proteins (in bact cw)
- Hooks (syphillis)
Name the 5 different examples of Penetration Factors (bacterial enzymes)
(are all enzymes; -ase)
1. Coagulase
- forms blood clot to stop BF to host defenses (ex: phagocytes; neutrophils/monocytes) cannot reach bacterium
- surround themselves in clot
2. Kinase
- break down clot surrounding bacteria so it can spread throughout body
3. Hyaluronidase
- breaks down hyaluronic acid in CT (connective tissue)
4. Collagenase
- breaks down collagen in CT
5. IgA Protease
- destroys IgA antibodies (so it can attach to mucous membranes in BV)
refer to slide 11, ch. 15 for helpful visual information
Name two ways in which pathogens are able to evade host defenses
- survive inside phagocyte
- antigenic variations
Describe how pathogens are able to survive inside a phagocyte (evasion of host defenses)
- pathogen escapes from phagosome before lysosomal fusion
- prevents fusion of lysosome with phagosome
- uses mycolic acid to inhibit lysosomal enzymes
Describe how antigenic variations help a pathogen evade host defenses
Include examples
pathogens change their surface antigens (antigenic determinants; ex: spike of viruses) through genetic mutations/recombination
is a key virulence factor seen in viruses (w/ spikes)
-> ex: infleunza virus, HIV
Define: Toxins
What can it do and provide examples
- poisonous substance (acts as Ag) produced by pathogens
- may produce fever, CV problems, diarrhea, shock (sudden large decrease in BP)
-> ex: Toxigenic bacteria vs. Nontoxigenic bacteria
CV = cardiovascular
Define: Toxigenicity
ability of a pathogen to produce a toxin
Define: Toxemia
presense of toxin in bloodstream
Define: Toxoid
What does it do and provide an example
- chemically modified toxin that is no longer toxic; injected
-> when injected, it stimulates the immune system to make Ab (how vaccines work)
-> example of artificially active immunity (injection of harmless Ag)
Define: Antitoxin
- Ab against a TOXIN (not against the bact); injected
-> ex: artificially passive immunity (injection of an Ab)
Toxins are a major virulence factors of ________, while antigenic variations are major virulence factors of _________
bacteria (only if theyre capable of making toxin)
viruses
In many cases, it is the _________ (not the ________) that creates the ____ of disease.
toxins
bacteria
symptoms
Name the 2 general types of toxins produce by some bacteria
exotoxins (3 types)
endotoxins
Toxins production may involved bacterial _____ that carry ________ for ________
plasmids
genes
toxins
What two ways do toxins get produced?
Briefly describe these two processes
1) Lysogeny involving phage conversion
-> bact. cell originally non-toxigenic -> bacteriophage inserts viral DNA carrying toxic genes -> inegrates into plasmid DNA (phage conversion) -> prophage -> host cell now toxigenic
2) DNA transfer via conjugation pilus
-> Donor cell (toxigenic) carries genes for toxin -> sents DNA to recipient cell (non toxigenic) via conjugation pilus -> gene integrates into recipient cell DNA -> now toxigenic
What are immunogens and what do they do?
What is an example of an immunogen?
act as antigens to triggest an immune repsone to produce Ab
-> Ex: toxins
immunogen = antigen = foreign substance = pathogen = toxin
Compare a strong immunogen from a weak immunogen
(Which one produces a fever and why? Provide examples of strong/weak immunogens)
Strong Immunogens
- good stimulator of an immune reponse -> Ab made -> no fever
- ex: protein toxins
- EXCEPTION!!!: Type I Exotoxin (Super Ag) which will produce a fever even though Super Ag are protein toxins
Weak Immunogen
- poor stimulator of immune repose -> no Ab made -> fever
- ex: lipid and polysacchiaride toxins (non-protein toxins)
Name the major properties of Exotoxins
(Include: Bacterial source, relation to microorganism, structural composition, toxicity, LD50, fever-producing, neutralized by antitoxin)
EXOTOXINS
Bacterial Source:
- secreted by living cells; mostly Gram-POSITIVE bacteria (sometimes gram-negative)
Relation to Microorganism:
- metabolic byproduct of live bacterium
Structural Composition:
- Proteins
Toxicity (ability to cause disease):
- High (bc they are strong immunogens that produce strong immune response)
LD50
- Small
Fever-producing:
- No (EXCEPT Super Ag; Exotoxin Type I)
Neutralized by Antitoxin:
- Yes (bc strong immune reponse produces many Ab)
Name the major properties of Endotoxins
(Include: Bacterial source, relation to microorganism, structural composition, toxicity, LD50, fever-producing, neutralized by antitoxin)
ENDOTOXINS
Bacterial Source:
- secreted by Gram-NEGATIVE ONLY
Relation to Microorganism:
- Found in LPS in gram-negative CW’s outer membrane; dying bacteria (endotoxin = in LPS = lipid = fever)
Structural Composition:
- Lipid
Toxicity (ability to cause disease):
- Low (bc they are weak immunogens that produce weak immune response)
LD50
- Large
Fever-producing:
- YES
Neutralized by Antitoxin:
- No (bc weak immune reponse produces no Ab)
Name the three different types of exotoxins secreted by mostly gram positive bacteria
Include the exotoxin type and exotoxin name
Type I = Super Antigen
Type II = Membrane-Disrupting (MD) Toxins
Type III = A-B Toxins
Describe Type I exotoxins
(Include Exotoxin Name, Characteristics/FXN, Mechanism of Action)
TYPE I
Exotoxin name
- Superantigen
Characteristics/FXN
- Ag that cause very strong immune reponse
Mechanism of Action
- Super Ag causes proliferation of T cells -> realease cytokines -> FEVER, nausea, vomitting, shock (large, rapid decrease in BP)
Describe Type II exotoxins
(Include Exotoxin Name, Characteristics/FXN, Mechanism of Action)
TYPE II
Exotoxin name
- Membrane-Disrupting (MD) Toxins
Characteristics/FXN
- Causes lysis of host cells by disrupting their CM
Mechanism of Action
- form channels in CM or disrupt phospholipids of CM
Describe Type III exotoxins
(Include Exotoxin Name, Characteristics/FXN, Mechanism of Action)
TYPE III
Exotoxin name
- A-B Toxins
Characteristics/FXN
- Consists of 2 parts (A and B)
- Most common type of exotoxin
Mechanism of Action
- inhibit protein synthesis in host cells
Describe the role (steps) of endotoxins in producing Pyrogenic Response (fever)
- Macrophage (phagocyte) ingests gram-negative bacteria
- Bacterium degraded in vacuole -> release endotoxins (LPS) of cw -> macrophage releases cytokines
- Cytokines go into blood and bind to hypothalamus receptors
- Reset body temp -> induce fever
Describe the pathogenic properties of Fungi
(Include: Kingdom, What do they do?)
Kingdom
- Kingdom Fungi
Characteristics
- x
What do they do
Fungal toxins
- contaminate food supply
- provoke allergic response
- carcinogenic (cancer-causing)
-> ex: aflatoxin
Methods of Escaping Host Defenses
- x
Describe the pathogenic properties of Parasitic Protozoa
(Include: Kingdom, What do they do?, Methods of Escaping Host Defenses)
Kingdom
- Kingdom Protista
Characteristics
- x
What do they do
- Feed on host tissue
- Damage intestinal lining
-> results in: diarrhea/dysentery
Methods of Escaping Host Defenses
- Grow in phagocytes (by inhibiting digestive enzymes in lysosomes)
- Antigenic variations
Describe the pathogenic properties of Parasitic Helminths
(Include: Kingdom, Characterisitcs, What do they do?)
Kingdom
- Kingdom Animalia
Characteristics
- Helminths = worms
- Not very pathogenic
What do they do
- Use host nutrients/tissue, but DON’t kill host
- Interferes with host food absorption (if large # in GI tract)
-> Results in: fatigue, weightloss
Methods of Escaping Host Defenses
- x
List and describe the major portals of exit for pathogens from the human body
Respiratory Tract
- by coughing and sneezing
Gastrointestinal Tract
- through feces and saliva
Genitourinary Tract
- through urine and secretions from genitals
Skin
Blood
- through anthropods that bite
- through needles or syringes
