Intro to bacteria Flashcards
Helicobacter pylori
stomach ulcers
helical shape
- penetrate stomach mucus
Proteus mirabilis
UTIs
long cell length
- cells align + use group swarming motility
cells can’t move in small group
Features prokaryotes vs eukaryotes
- cell wall
- nucelar membrane
- nucleolus
- no. of chromosomes
- mitochondria
- ribosomes
P = contains peptidoglycan E = no peptidoglycan
P = absent E = present
P = absent E = present
P = 1 E = >1
P = absent E = present
P = 70S E = 80S
cell envelope
provides interface between bacteria + enviro
maintains cell integrity
protein or sugar capsule
external structures for adhesion or motility
(pili, flagella)
bacteria in distilled water
can maintain shape + integrity
gram +ve
- features
- examples
thick cell wall
multiple peptidoglycan layers
interspersed w/ teichoic acids (anchor peptidoglycan to membrane)
Staphylococcus
Streptococcus
gram -ve
- features
- examples
think peptidoglycan wall
enclosed by OM of LPS
no teichoic acids
periplasmic space contains peptidoglycan
Escherichia
Pseudomonas
Gram staining
- heat fix bacterial smear to glass
- stain w/ crystal violet
= violet cells - fix w/ Gram’s iodine
= violet cells - de-colourise w/ alcohol
= violet or colourless - stain w/ safarin
= red - wash with water
= +ve = purple
-ve = red
peptidoglycan
- structure
made of linear glycan chains
cross-linked by short peptide chains
glycan
- structure
alternating units of:
N-acetylglucosamine
N-acetylmuramic acid
joined by beta 1,4-glycosidic links
antimicrobial agents acting on peptidoglycan
- how?
- examples
some work intracellularly
- prevent precursor synthesis
some prevent cross-linking
penicillin
vancomycin
adding beta-lactam AB to a cell
e.g. in S. aureus
prevents pentaglycine cross link
weakens cell wall
-> cytoplasmic membrane forces its way out
cell wall breaks down
-> cytoplasmic membrane now outermost structure
= spheroplast
= osmotically fragile
- easily take up water
- > bursts
Lysozyme in S. aureus
breaks glycosidic bonds between sugars
-> breaks down peptidoglycan cell wall
cytoplasmic membrane
highly selective barrier
phospholipids + proteins
larger molecules must be transported
no cholesterol
v fluid
site for energy generation
cytoplasmic membrane
- site for energy generation
charged ions e.g. H+ cannot move freely across membrane
-> gradients form
efflux of H+
- > electrochemical gradient (proton motive force)
- > powers processes
LPS
endotoxin
feature of gram -ves
can continue to cause damage even after cells die
-> due to toxic effect of LPS OM
(AKA endotoxin)
(LPS isn’t removed by sterilisation)
LPS
structure
O antigen
= repeating chains of polysaccharides
<200 residues
Core
= ~5 sugar residues w/ side chains
Lipid A
= dimer of phosphoglucosamine residues w/ 2 fatty acid chains linked to each sugar residue
LPS
- general effects
fever
intravascular coagulation (activates blood clotting factors)
vasodilation
-> hypotension (low BP)
shock
-> due to hypotension
CAN BE FATAL
N. meningitis
gram -ve
septicaemia phase as part of pathogenesis
sheds LPS into blood during septicaemia
-> complications
treatment w/ ABs
- > enormous LPS release
- > fatal?
capsules
-features
many gram-ve and some gram +ve
produce extracellular polysaccharide (EPS)
discrete capsule or generalise slime layer
capsules (EPS)
- functions
adherence
resistance
- to AMs, desiccation, macrophages
immune evasion + virulence
capsules
- example
S. pneumoniae
- needs capsule for pathogenicity
-> shields cell from IS detection
bacterial chromosome
nucleoid
= chromosomal DNA localised to are of cytoplasm + anchored to cytoplasmic membrane
series of highly folded loops
- but NOT bound a membrane
plasmids
autonomously replication extrachromosomal DNA
circular dsDNA
HGT between species
accessory functions conferring advantage
- AB resistance, produce toxins
