BacT Lec 3 Flashcards
*Pathogenicity
The ability of a pathogen to produce a disease by overcoming the defense mechanisms of the host
Virulence
The degree of pathogenicity (factors present in an organism that makes it to cause disease)
*Properties or traits found in isolates that cause disease but which are not found in isolates of the same species that lack ability to cause disease
Bacterial Virulence Factors
To cause disease a pathogen must:
1) Gain access to the host
2) Adhere to host tissue
3) penetrate or evade host defenses
4) Damage the hose - directly or accumulation of microbial wastes
Preferred portals of entry
Mucous membranes
Skin
Parental route
ID50
Number of microbes required to produce infection in 50% of the population
LD50
The amount of toxin or pathogen necessary to kill 50% of the population in a particular time frame
Adhesins
Surface projections on pathogen, mostly made of glycoproteins or lipoproteins. Adhere to complementary receptors on the host cells
Adhesins can be part of:
Glycocalyx
Fimbriae (also pili and flagella)
What can biofilms provide?
attachment and resistance to antimicrobial agents
5 ways to overcome host defenses
1) Capsule
2) Cell wall components
3) Antigenic variation
4) Penetration into the host cell cytoskeleton
5) Production of enzymes
Incasins
Alter host cell actin to enter a host cell (Salmonella)
Use actin to move form one cell to the next (listeria)
Three ways intracellular bacterial survival following phagocytosis
Escape from phagocytic vacuoles into cytosol
Prevention of lysosomal fusion to phagosomes
resistance to hydrolytic enzymes
Exoenzymes
Coagulase Kinase Hyaluronidase Collagenase IgA protease
Two qualities that bacteria underlie the means by which they cause disease
Invasiveness
Toxgenesis
Two types of invasiveness
Colonization
Invasion
Colonization is?
Adherence and initial multiplication
Invasion is
Production of extracellular substance which facilitate invasion
Two types of toxigenesis
Endotoxins (Gram-neg only)
Exotoxins (Gram-neg and Gram-pos)
Quorum sensing
Bacteria remain innocuous until they reach a certain population and then ambush the immune system
Non selective culture media
Liquid (broth)
Solid (Agar media)
Trypticase soy agar with blood (blood agar)
How is liquid broth used?
To help bacteria to overcome stress that they have been experience so that we can get them to grow. No isolation is done.
Most common culture media
Trypticase soy agar with blood (blood agar)
What is the difference in selective media and non selective media?
Non selective media can culture most all bacteria.
Selective media excludes bacteria depending on the type
Selective culture media
PEA (Phenylethyl Alcohol Agar)
MacConkey Agar
Hektoen Entrtic Agar
What kind of bacteria does PEA (Phenylethyl Alcohol Agar) culture?
*Gram- Positive
What kind of bacteria does MacConkey Agar culture?
*Gram-Negative
What is unique about MacConkey Agar?
It is *selective for Gram-Negative and is a *differential media (lactose and neutral turn red & fermentation turn pink)
What bacteria does Hektoen Enteric Agar media selective for and differentiates?
E. coli (differentiates from salmonella - black colonies)
What makes bacteria identification easier?
More knowledge of the bacteria you are trying to isolate.
Most accurate bacteria identification.
MALDI-TOF
List the biosafety Levels form lowest to highest
BSL 1, BSL 2, BSL 3, BSL 4
What is the purpose of biosafety levels?
Minimize potential exposure to a biohazard for lab personnel and others
What level do all laboratories operate on?
BSL 2
What level is for agents that there is no treatment available.
BSL 4
List examples of BSL 3
Brucella suis, Mycobacterium tuberculosis
List examples of BSL 4
Ebola virus, Small pox
What has to happen for a microbe to cause disease? Also know as *Virulence Factors
Gain entry Enough population (minimal infectious dose) Adherence Overcome host defenses Damage host Exit host
What bacteria was first found to have the characteristic of quorum sensing?
Vibrio fischeri
What is the unique feature of Vibrio fischeri?
It is quorum sensing is shown through bio-luminescence. Only when it reaches a certain population does it become bio-luminescent.
List the ways bacteria can cause damage.
Direct damage to host cell
Using host’s nutrients
Produce toxins
Induce hypersensitivity reactions
What are some direct damage to the host cell?
Growth and replication in host cells: result in host cell lysis
Penetration through host cells (mucosa organs) causes damage
Lysis of host cells to obtain nutrients
What ways can microorganisms use the host’s nutrients?
By producing *siderophores that bind iron form host proteins and are then absorbed by the bacteria.
Give an example of siderophores and what kind of bacteria is it usually found in?
Enterobactin found primary in Gram-negative
Bacterial factors that disturb host functions
Protein *exotoxins
Hydrolytic Enzymes
Products that evoke aberrant host response
*What are some products that evoke aberrant host response?
- Cross-reactive antigens (autoimmunity)
- Superantigens
- Endotoxin (Gram-negative)
Describe endotoxin
LPS, Lipid A part: relase upon cell death; symptoms due to vigorous inflammination. Massive release: endotoxic shock.
*Difference between endotoxin and exotoxin.
Exotoxin are proteins produced inside bacteria as part of growth and metabolism then secreted outside the cell.
Endotoxins are lipid portions of LPSs that are part of the outer membrane in Gram-negative and are liberated when bacteria dies and cell wall breaks apart.
*Poisonous substances produced by microorganisms are called
*Toxins
*Toxemia refers to
*The presents of toxins in the blood
*Ability to produce toxins is called
*Toxigenicity
*T:F Exotoxins are not bacteria
*True
Exotoxins are produced by bacteria and cause disease symptoms.
*Antibodies produced against exotoxins are called
*Antitoxins
How are toxins named?
Named according to type of cell they attack
What are the three basic types of exotoxin based on?
Structure and function
What are the three basic types of exotoxin based on structure and function?
A-B toxins (type III)
Membrane disrupting toxins (Type II)
Superantigens (Type I)
Descriptive terms that indicate site of some well defined protein toxins
Neurotoxins- attack neurons
Leukotoxins- attack blood
Enterotoxins- attack gastrointestinal
Cytotoxins- attack cells
What are the two components of the A-B Toxins and what do they do?
The A polypeptide is the *enzyme active and the B polypeptide is a *binding component. A subunit enzymatically kills the cell.
Membrane disrupting toxins do what?
Type II toxins that disrupt host cell plasma membranes
Superantigens do what?
Type I toxin: special type of exotoxin: nonspecifically stimulate T-cells. Cause intense immune response die to release of cytokines from host cells.
Draw out Table 15.3
Refer to lecture 3 slide 30 BacT
Draw out table 15.2 (Special attention to Botulism, diphtheria, clostridium perfringens, Food poisoning, Toxic shock syndrome)
Refer to lecture 3 slide 31 BacT
How can bacteria acquire virulence factors?
- Encoded on chromosomal DNA
* Encoded on bacteriophage DNA, Plasmid DNA or Transposons
Bacteriophages
Are virus particles which attack bacteria.
Phage can be transmitted to nonpathogenic strains making them virulent
Lysogenic conversion with bacteriophages can?
Result in bacteria with virulence factors, such as toxins, fimbriae or capsules
Bacteriophage genes
Corynebacterium diphtheria (Diphtheria toxin) Clostridium botulinum (Botulinum toxin) E. coli O157 H7( Shiga toxin) (haemolytic uremic syndrome)
The process by which DNA is transferred form one bacterium to another by a virus is called
Transduction
The process by which one bacterium (bacterium with a fertility factor) transfers genetic material to another through direct contact.
Conjugation
The genetic alteration of a cell resulting form the direct uptake and incorporation of exogenous genetic material form surroundings and taking up through the cell membrane.
Transformation
