what is the purpose of a gram stain?
allows us to broadly differentiate bacteria based on cell wall structure
how does a gram stain work on gram positive vs gram negative bacteria
-methanol added to cell surface fixing cells to plate
-crystal violet (violet colour) added and left for 1 min
-iodine added, binding crystal violet to gram-positive cells (1 min)
-wash with ethanol for 20 seconds, gram positive bacteria retain crystal violet while gram negative has the stain washed away
-add safranin counter stain, gram positive cells absorb safranin but remain dark purple while gram negative cells become pink in colour
why does gram negative and gram positive cells react differently when subjected toa gram stain?
gram positive bacteria has far more peptidoglycan layers and no outer membrane, allowing for deeper penetration of crystal violet and retention. gram negative bacteria has less peptidoglycan layers and an outer membrane which allows the decolouriser (ethanol) to remove loosly trapped stain from membrane
what are the 3 types of bacteria phylogeny and gram classification?
-actinobacteria/actinomycetota high GC content genome
-firmicutes/bacillota low GC content genome (mostly monoderm)
-tenericutes lack cell walls (not staining gram positive)
what is diderm bacteria
gram negative bacteria, having two membranes (outer and normal)
what is the lahyers of gram positive bacteria cell envelope from outer most to inner most
-pili, flagella (attachment and motility)
-polysaccharide capsule (provides protetion, immune evasion, desiccation resistence)
-S-layer (protection, membrane stabilisation, adhesion)
-thick peptidoglycan layer (gives cell shape, resistence to osmatic pressure, highly conserved nd essential, major target of immune system)
-teichoic acids (negative charge, cell wall flexibility)
0cell membrane (permiability, ion gradient)
what is the peptidoglycan layer of a bacteria cell
-complex variable and dynamic structure
-basic conserved structure with glycan chains with amin acid cross-links and much variation with different structures being called chemotypes
-changes to glucan bacbone by N-deacetylation, N-glycolylation, N-acetylation) via amino acid side chains
-constintly remodeeled with existing PG cleaved to allow for insertion of new subunits
-L-form bacteria lacking PG can be isolated for many species in lab, may play role in pathogenesis
what is the PG layer of bacteria made of
-glycan chains, repeating units of N-acetylglucosamine and N-acetylmuramic acid
-peptide cross bridges, often D-amino acids
-cross linking reactions catalysed by penicillin binding proteins (PBPs) a major target of antibiotics
-target for lysozyme and other enzymes (lysozyme in saliva tears, sweat etc)
what are teichoic acids
repeating units of glycerol or ribitol linked by phosphodiester bonds
-can form complexes with divalent cations Mg2+ and Ca2+
-role poorly understood
what two examples exist that go against gram positive cell envelope structure? how do they differ
mycobacteria and mycoplasma
-do not stain well due to thick waxy mycolic acids, have to be staind with acid-fast stains
-mycolic acids link to peptidoglycan layer via arabinogalactan
what does gram positive bacteria in the human microbiome do
usually commensal, can be benifical can be opertunistic pathogens
firmicutes:bacteroidetes ratio in gut microbiome important, high firmicutes is associated w obesity and inflammation
what bacteria inhibits tooth decay? whats the name of pathogens that accelerate the decay of teeth
oral commensal streptococci inhibit cariogenic pathovars (tooth decay pathogens)
what is the name of the pathogen that causes anthrax symptoms? what are the main routes by which it causes harm
-bacillus anthracis
-spores ingested and germnate in host digestive tract leading to gastrointestinal anthrax
-spores inhaled and germinate in host respiratory tract making inhalation anthrax (deadliest)
-spores enter cut or open wound leadig to cutaneous anthrax
generally acquired by handling infected animals or contaminated animal products
how does Bacillus sporulation occur?
-vegatitive cells differentiate into endospores via a tightly regulated process, asymmetric cell divison leads to 2 different cell types being made
-mature spores are metabolicly dormant and resistant to many enviromental stress factors
-in favorable conditions the spores germinate into vegatative cells, restarting the cycle. anthrax is made somehwere along the path
what is anthrax toxin
a 3 protein exotoxin (secreted by bacteria) with a active part and a binding part, (AB toxin type)
-protective antigen (PA) binds to eukaryote cells and forms pore (heptamer_ for translocation of LF and EF into cell
-lethal factor (LF) adenylate cyclase which is lethal in lab animals
-edema factor (EF) an andoprotease which causes edema in lab animals
what is listeriosis
a disease caused by listeria monocytogenes
can cause mild-severe intestinal illnesses suc as diareah and vomiting
if spread can cause flu like symptoms and miscarriage
what problems do listeria biofilms do
they are a huge problem for food processing as they are resistant to antimicrobials, grow at low temp, high salt, and low water. also grows in organism gut mucosal cells.
regulated by quorum sensing where listeria uses a autoinducing peptide to regulate group behaviour
what is a dichotomous key
tool or approach used to identify/classify organisms
what is a monoderm and diderm
cells with one or two membranes respectivly
what is a chemotype
a functionally or morphologicaly equivelent part of a microbial cell thats chemmicaly distinct
what is L-form bacteria
bacteria cells that lack a cell wall or peptidoglycan layer
