Mechanisms of Pathogenicity Flashcards
Define pathogenicity
ability to cause disease
Define virulence
the extent to which the microorganism is pathogenic
Define virulence factors
molecules/structure produced by pathogens that contribute to their pathogenicity
Some microorganisms have a ____ portal of entry & only capable of causing disease via a ____ route
preferred, specific
Ways for pathogens to enter the host cell (5)
Most of the time: mucous, skin, parenteral route via mouth
Bypass ways: surgical sites, implants
What determine a pathogen’s tropism? (6)
- distribution of cell receptors for microbes
- correct host cell types
- competing microbes
- nutrients for growth
- physical and innate defenses
- environmental condition (eg. pH)
How do pathogens remain at the site of infection and do not have to spread to cause disease?
Produce toxins that get into cells
What is the first step of infection?
Adherence
How does adherence work?
structures on the pathogen called adhesins or ligands (most are glycoprotein or lipoprotein) bind to host cell’s receptors (most are sugars)
What are the factors that allow bacteria to penetrate host defenses? (10)
- capsules (or glycocalyx)
- cell wall components
- biofilms
- enzymes
- invasins
- superantigens
- toxins
- secretion system
- antigenic variation
- intra/extracellular growth
How do capsules (or glycocalyx) protect bacteria?
prevent the phagocyte from recognizing and ingesting the bacteria
How do cell wall components protect bacteria?
Fc receptors on bacterium binds to Fc area of an antibody to prevent opsonization
How do biofilms protect bacteria?
Reduces antibiotic penetration
What are the three exoenzymes bacterial cells release? Describe the function of each exoenzyme.
Leucocidin: destroy WBC
Kinase: break down fibrin and dissolve clots formed (important for spread)
Hemolysin: Break down RBC
How do invasins (surface protein) protect bacteria?
Activate and rearrange actin and facilitate bacterial engulfment and movement
How do M protein (a cell wall component) protect bacteria?
- heat and acid resistant
- allow attachment of the bacteria to epithelial cells and inhibits phagocytosis
What are 3 types of exotoxins?
cytotoxins, neurotoxins, enterotoxins
How do secretion system protect bacteria?
Genes encoded on their chromosomes for pathogenic characteristics
(Eg. type III secretion apparatus enables a bacterial cell to inject protein into a host cell)
How do antigenic variation protect bacteria?
Immune system sees old pathogens as new ones as they change the makeup of their antigens when replicating
Define obligate intracellular bacteria.
Bacteria that can only grow inside of host cells
eg. Chlamydia, Rickettsia
How do M protein as a cell wall component protect bacteria?
Allow attachment of the bacteria to epithelial cells and inhibits phagocytosis
How do mycolic acids as a cell wall component protect bacteria?
waxy substances in cell walls can prevent bacterium to be digested easily
(eg. M. tuberculosis)
What are the three methods of horizontal gene transmission? Define each.
Conjugation: transfer of plasmids
Transduction: transfer of DNA from one bacterium into another via bacteriophages.
Transformation: uptake of naked DNA from the environment around the bacterium (extracellular)
Define plasmid.
small circular DNA molecules separated from the main bacterial chromosome
