Basic concepts Flashcards
Pathogenicity vs virulence
Pathogenicity= ability to cause disease Virulence= extent of disease
Pathogen
organism causing damage and disease (symptoms / signs of illness) via interaction with host
List five broad classes of human pathogens
viruses bacteria fungi protozoa helminths
Gram positive organisms stain ______ with Gram staining whereas gram negative organisms stain ______
purple/blue; pink/ red
Gram positive organisms have a thicker ________ layer than Gram negative organisms. This blocks the decolorization step of the Gram staining process
peptidoglycan (murein)
List the basic steps in Gram staining protocol
- fixation
- stain with crystal violet
- iodine treatment
- decolorization
- safranin counter stain
Findings of intracellular gram negative diplococci within PMNs on gram stain of urethral discharge in symptomatic men is diagnostic for ________
Neisseria gonorrhoeae
List features of Gram positive bacteria
- two layers: thick peptidoglycan layer; cytoplasmic membrane
- teichoic acids
- adhesion to host cells by adhesions and teichoic acids
List features of Gram negative bacteria
- three layers: outer membrane; thin peptidoglycan; inner membrane
- endotoxin/ LPS
- periplasmic space
- porins
- attachement to host cells by fimbriae, adhesins
Describe phases of standard bacterial growth curve
- Lag phase: little cell growth/ division as cells adapt
- Exponential phase: maximal division rate
- Stationary phase: nutrients exhausted, waste products accumulate, new cells= dying cells
- Death phase: number of nonviable cells > viable cells
Mesophiles grow best at ________ degrees celsius and include most human pathogens
20-45 C
_______ grow at temperatures below 20 C and are a major concern in _______ and blood products
Psychrophiles; refrigerated foods
Thermophiles grow at temperatures of 45-60 C and are a concern in _________
food processing/ canning
________ grow at temperatures greater than 60 C
Stenothermophiles
Why are anaerobes unable to grow in the presence of oxygen?
lack enzymes to detoxify reactive oxygen species
most human pathogens are ________ for oxygen
facultative
_______ require reduced oxygen levels for maximal growth
Microaerophiles
_______ grow best under conditions of increased carbon dioxide
Capnophiles
Distinguish plasmids from transposons
- Plasmids: 5-100 genes passed during cell division or transferred between bacteria during conjugation or transformation
- Transposon: 1-10 gene element on plasmid or chromosome that can move to other sides in DNA; does not replicate independently
Distinguish: transformation, transduction, and conjugation
Transformation – mediated by free (naked) DNA
Transduction – mediated by bacterial virus (bacteriophage)
Conjugation – mediated by transfer apparatus, e.g., pilus
One way of maintaining transferred DNA is integration into a replicating DNA molecule via _______
genetic recombination
Distinguish generalized transduction from specialized transduction
- generalized transduction: mediated by lytic phase; any portion of degraded bacterial DNA can be repackaged into assembling phage head
- specialized transduction: mediated by lysogenic phage, imprecise excision carries along bacterial DNA from areas adjacent to phage integration site
Define lysogenic conversion
lysogenic phage infection changes the phenotype of the host bacterium, sometimes incurs new virulence factors. Ex diptheria toxin, cholera toxin
Describe antigenic variation as a mechanism of escaping host defenses.
Organism expresses different phenotypes- homologous proteins-> antigenic variation. Change pilus so host response is no longer effective. Evade adaptive host response
