Please enable JavaScript.
Coggle requires JavaScript to display documents.
Micro - Bacterial Morphology + Physiology (i) (Capsules + slime (capsules…
Micro - Bacterial Morphology + Physiology (i)
intro
morphology = shape + structure
NB to understand in order to eradicate using antibiotics
bacteria = prokaryotes
have a cell wall
EM can visualise viruses + small bacterial cell structures (e.g. appendages)
The gram stain
NB differential staining method
method
crystal violet
stains gram +ve (e.g. staph) + -ve (e.g. E Coli) violet
forms crystal-iodine complex
iodine
fixative, gets trapped inside
alcohol
differentiator
gram +ve cells have low lipid content in cell envelope so get dehydrated by alcohol + made inpermeable (i.e. alcohol gets trapped inside)
gram -ve cells have high lipid content in cell envelope - lipids get extracted by alcohol, which permeabilises the membrane
crystal-iodine complex diffuses out (decolourised)
some bacteria don't stain using this method...
mycobacteria
waxy cell envelope
use Ziehl-Neelsen instead
mycoplasma
no cell wall
Bacterial cell shapes
cocci (spherical)
diplococci (in pairs)
streptococci (gram +ve in chains)
staphylococci (gram +ve in clusters)
sarcinae (groups of 4)
bacilli (rod)
streptobacilli (in chains)
coccobacilli (truncated)
spirochetes (spiral)
e.g. treponema pallidum
vibrios (curved)
Spores
produced by some gram +ves
e.g. all Clostridiums
C tetani
contracting paralysis
C botulinum
flaccid paralysis (botulism)
tinned food, bad pasteurisation
C perfringens
gas gangrene (soft tissue infection)
bacillus anthracis
causes anthrax (pul or cut)
in soil, wool, leather (farmers @ risk)
protection from adverse conditions
spore itself is harmless
formation triggered by adverse environmental conditions
bacterium remains dormant until transited to a favourable environment where it can germinate
surrounded by peptidoglycan
rich cortex + keratin-like coat (resilient, protects genomic material)
Capsules + slime
capsules = tightly associated, part of envelope
polysacc/protein layers
surround many bacterial cells (e.g. N meningitides)
slime = loosely-associated, extracellular
protect from phagocytosis, antibiotics
help adherence/anchorage
Biofilms
= community of cells encased in slime layer stuck to a surface (e.g. hearts valve, prosthesis, pseudomonas aeruginosa on CF lungs, S epidermis - coag -ve - on catheter, MRSA)
involved in majority of bacterial infections treated by clinicians
cause chronic infection
Tx
remove device/prothesis
antibiotics, but harder because...
cells in biofilms are metabolically different
no cell wall synthesis (cell wall synthesis inhibitors ineffective)
slow penetration (higher dose needed)