Lesson 2.5 & 2.6 - Pathogenicity & Antimicrobials Flashcards
Define pathogenicity
Ability of an organism to cause damage / disease to a host that it infects
Define virulence
Degree of pathogenicity; a phenotype
Define avirulence
Not a pathogen
Define disease
Disruption of homeostasis
Pathogens express genes that code for ____________
virulence factors
Virulent pathogens have a ____ threshold than less virulent relatives
less; that means it takes fewer to cause disease
Some pathogens employ a _____ growth strategy to avoid immune system
slow
Treponema pallidum incites…
Syphillis
LD50
lethal dose of LETHAL pathogens; expressed as # of organisms required to kill 50% of test animals
Which is more virulent: Streptococcus pyogenes OR Salmonella enterica serovar Typhimurium
Streptococcus pyogenes (according to LD50)
ID50
infectious dose of NONLETHAL pathogens; expressed as # of organisms to cause illness in 50% of test animals
Opportunistic pathogens
Avirulent organisms that cause disease when host’s immune system is weakened; severe burns may result in this
What causes oral thrush / candidiasis in HIV patients?
Candida albicans
What causes lung infections of cystic fibrosis patients?
Psuedomonas aeruginosa
Virulence Continuum
Lactobacilli, Candida albicans, Clostridium difficile, Pseudomonas aeruginosa, Bordetella pertussis, Yersinia pestis, Francisella tularensis
Types of virulence factors
Adhesions, extracellular enzymes, exotoxins, endotoxins, antiphagocytic factors, biofilm formation, phase variation / antigenic shift
Adhesion factors
Specialized attachment proteins on fimbriae, flagella & capsule;
Viruses & bacteria have lipoproteins & glycoproteins that bing to host receptors
Neisseria gonorrhoeae
- STI - gonorrhea
- Fimbriae adhesion proteins
- Binds to genitourinary system lining cells
Extracellular enzymes
Released by BACTERIA to degrade host molecules and evade immune system
Hemolysins
cause lysis of RBCs; extracellular enzyme
Hyauronidase
Degrades hyaluronic acid; extracellular enzyme
Connective, epithelial, and neural tissue
Collagenase
Degrades collagen; extracellular enzyme
Coagulase
Promotes blood clots; extracellular enzyme
Kinase
digest blood clots; extracellular enzyme
Necrotizing fasciitis
Deeper skin & connective tissue; cysteine protease
Toxins
- interfere with biochemical, cellular, enzymatic, and metabolic process
- enter bloodstream & carried to other parts of body
- some enzymes act as toxins, some toxins have enzymatic activity
Exotoxins
- proteins (most are enzymes), soluble, diffusible, high toxicity
- inhibit metabolic function
- produced by Gram (-) AND Gram (+) bacteria
- often exotoxin causes symptoms, not bacterium
Cytotoxins
kill host cells or inhibit function; type of exotoxin
Neurotoxins
interfere with normal nerve impulse transmission; type of exotoxin
Enterotoxins
affect epithelial cells of GI tract; type of exotoxin
Antitoxins
antibodies that neutralize toxin
Toxoids (& example)
Inactivated toxins used as vaccines
e.g. Tdap (Diptheria, Tetanus, Botulism)
E. coli O157:H7
- Can lead to post-diarrheal hemolytic uremic syndrome (HUS)
- Produces cytotoxin (protein synthesis); Shiga-toxin
- Inflammatory response
Post diarrheal hemolytic uremic syndrome (HUS) characteristics
-
Thrombocytopenia
- Decrease in platelet #
-
Microangiopathic hemolytic anemia
- Misshapen/fragmented cells may clog kidney capillaries
- Acute renal injury
A B Toxins
- Subunit A = enzymatic acticity, catalyzes cAMP from ATP
- Subunit B = binds & transfers
cAMP function
- cyclic AMP; signals cells to dischard gluids into intestinal lumen
- Severe watery diarrhea
Vibrio cholerae
cholera toxin, enterotoxin
Botulinum Toxin
- Neurotoxin by Clostridium botulinum (when spores germinate)
- Binds to motor neurons & prevents acetylcholine release
- Paralysis & suffocation (diaphragm)
- 10 ng = lethal
Tetanus Toxin
- Neurotoxin by Clostridium tetani
- Binds to motor neurons
- Uncontrollable muscle contractions - can break bones
- 50 ng = lethal
Endotoxins
-
Gram (-) cells die, release lipid A
-
Causes macrophages to release cytokines
- Travel throughout host
-
Causes macrophages to release cytokines
- Low toxicity; fatal in high concentrations
Increased cytokines lead to…
Blood vessel dilation & leakage, fever, coagulation, hemorrhaging, inflammation, shock
Antiphagocytic factors
Characteristics that inhibit phagocytosis
Capsule
Protects bacterial cell & evades host immune system
($) Examples of killing/injuring phagocytes
- Pseudomonas aeruginosa exotoxin A kills macrophages
- Pathogenic staphylococci produce leukocidin
- Pathogenic streptococci produce streptolysin
- Pyogenic cocci (Gram +, produce pus) produce hemolysins
(5) Mechanisms of Avoiding or Confusing Phagocytes
- Some don’t illicit overwhelming immune response
- Release compounds that inhibit phagocyte chemotaxis (send pathogens wrong direction)
- Camouflage
- Cover surface w/ host cell proteins
- Prevent phagolysosome formation
Phagolysosome (& [3] resistance mechanisms)
- Phagocyte with lysosome (degradative enzyme)
- Some bacteria inhibit lysosome/phagosome fusion
- Some inactivate enzymes
- Some escape
Legionella pneumophilia
Example of bacteria surviving in phagolysosome
Biofilms characteristics
- Microbial community (mono or poly - physiologically integrated)
- Extracellular polysaccharide
- Prevents antibiotics penetration
- Promotes HGT
- Associated with chronic infections
Quorum Sensing
mechanism by bacteria to monitor population density & regulate behavior
Behavior of quorum sensing (4)
- Biofilm recruitment
- conjugation
- pathogenesis
- production of extracellular polysaccharides
Types of autoinducers (3)
- N-acylhomoserine lactones (AHLs)
- Autoinducing peptides
- Autoinducer-2
Antigenic Variation & Types
- Bacterial pathogens may change surface to avoid host immune response
- Fimbriae, outer membrane proteins, capsule, flagella
Antigenic Drift
Viral mutation during replication
Antigenic Shift
Reassortment; both viral types incorporated
