Bacterial Properties and Disease Flashcards
Describe the different shapes of bacteria?
Coccus - spherical, staphylococci, streptococci (both gram positive)
Bacillus - rod - can be both gram positive and gram negative
Spirilli - gram-negative, elongated structure, spiral shaped rigid cells.
Define Gram-Negative?
Dye lost from thinner peptidoglycan (sugar-peptide link molecule gives bacteria its rigidity and shape). These absorb a counterstain and appear pink. These absorb dye differently as they have 2 membranes, that form the cell envelope.
Between the two membranes is a periplasm - containing peptidoglycans. Outer membrane = Lipopolysaccharide (LPS) v potent agonist in the innate immune response - our immune system detects v low amounts of LPS and initiates a proinflammatory immune response. Can be more difficult to get antibiotics through the 2 membranes
Examples of Gram-negative?
E.coli - (epec - diarrhoea, ehec - toxin, dysentry, kidney failure). Salmonella (food poisoning or typhoid), Shigella (dysntery), Vibrio Cholerae (cholera), Neisseria meningitis/gonorrhea.
Define Gram-Positive?
peptidoglycan in cell wall retains the dye, high peptidoglycan = deep violet, Neisseria (meningitidis + gonorrhoeae), Haemophilus Influenzae, E.Coli, Salmonella spp., Vibrio Cholerae, Shigella.
Staphylococcus aureus , Streptoccocus pneumoniae, Streptococcus pyogenes, Clostridium (difficile, tetani, botulinum, pergringens)
Which bacterium is neither Gram-Positive/Gram-Negative?
Myobacterium - neither gram positive/negative, Tuberculosis + Leprae, waxy cell wall.
Which bacterium have main life cycle inside the cell?
listeria, shigella, salmonella, mycobacteria, chlamydia - predominantly replicate within a host cell. They have different methods inside the cell. Coxiella likes to survive in the phagolysosome, salmonella + mycobacteria - take place in a vacuole and prevents fusion and degradation in lysosomes. Listeria and Shigella - break down vacuole and replicate inside the cell cytoplasm.
Which bacterium have main life cycle outside the cell?
staphylococcus, streptococcus, yersinia, neisseria - replicate or persist outside host cells i.e. in tissue.
Why use gram stain?
distinguishes between 2 different kinds of bacterial cell walls. Bacteria first stained with violet dye and iodine, rinsed with alcohol, then stained with red dye. Gram-negative/positive bacteria can respond differently to different antibiotics -
How do bacterial pathogens cause disease?
colonize surface of bodies, must persist against host defenses, replicate + acquire nutrients, disseminate within host cells/tissues/organs, cause disease - produce toxins that kill host
How do Salmonella and Shigella enter a cell?
using flagella - long thin tail with motors for movement and needle like structures virulence proteins - injectisome, that injects proteins into the plasma membrane that forms a pore through which the bacterium attaches and transfers proteins from the bacterial cell into the host cell (across 3 membranes) and is taken up into the cell via endocytosis.
Injectisome tricks the host cell into actin polymerisation, driving membrane ruffling as actin pushes against the plasma membrane this traps the bacterium and bacteria is brought into the cell.
How big is the bacterial genome?
Genomes of bacterial pathogens enocde 500-4500 proteins. 40% are core (housekeeping) + rest accessory genome = gene repetoire
Describe Vertical Transmission?
Replicate by binary fission → inheritance of a copy of the genome from parent to daughter (identical).
What is Horizontal Gene Transfer?
Transformation - naked DNA uptake from cell, goes outside the cell
Conjugation - direct transfer of plasmid from one bacterium to another by formation of a mating bridge. Plasmids frequently confer antibiotic resistance.
Transduction - phage mediated transduction - viruses infect bacterium and assemble viral particles, and incorporate bacterial DNA and transmit that from bacterium to bacterium.
Pathogenicity island - distinct genetic elements on the chromosomes of a large number of bacterial pathogens. These encode virulence factors and insertion sequences and are found near/within tRNA genes.
What is Infectivity?
general features that favours infection
Transmission to host Ability to colonise host Tropism - finding a unique niche (in/out of cell) Replication Immune evasion
What is Virulence?
features that enhance disease causation:
Toxin production - pneumolysin - chlosterol dependent pore-forming toxin affecting lung architecture.
Enzymes that degrade host molecules - hyaluronan lyase degrades hyaluronic acid matrix for nutrition.
Interruption of host processes - superantigens made by S.Aureus interfere with normal T cell function.
Complete immune evasion - S. Aureus leukocidins leading to neutrophil death and abscesses.
What is the Infectious Dose?
The number of bacteria required to initate an infection, this can be affected by:
Route of transmission
Ability to colonise host
Tropism + motility
Replication speed
Immune evasion at site.
Note if you have a low infectious dose you have high infectivity (less required to infect), if you have a high infectious dose you have low infectivity.
