Lectures 6-10 Flashcards
Resolution equation:
R = 0.61 λ / NA NA = n sin θ θ = half the angle that light enters the lens n = refractive index of the medium between subject and lens
Long and bendy morphologies:
Vibrios, spirillas, spirochetes
Arrangements/groupings:
Pairs (diplo both)
Clusters (staphylococci)
Chains (strepto both)
Structure of bacterial cell wall:
Peptidoglycan - NAG NAM carbs glued together with proteins.
Gram positive bacteria:
Multiple layers of peptidoglycan. Teichoic acids keep layers together and give the walls negative charge.
Ex: pneumonia, s aureus, botulinum, anthrax
Gram negative bacteria:
One layer of peptidoglycan and one phospholipid membrane.
Ex: gonorrhea, flu, e coli, cholera
Learn Gram stain
Acid fast stain:
For fatty cell walls that repel Gram stains. Primary dye is carbol-fuschin, which has a high affinity for waxy mycolic acids. Decolour with acid-alcohol. Counterstain with methylene blue.
Positive stains red, negative stains blue.
Ex: tuberculosis, leprosy
Glycocalyx:
Sugars and proteins. Increases pathogenicity. May produce biofilms, which can help bacteria stick to a surface.
Ex: S. mutans and plaque (calcified capsules)
Negative stain:
Allows visualization of the glycocalyx. Nigrosin dye is bulky and negative charged so it doesn’t stick to bacteria. Thin film prep without fixing cells. Additional staining (CV) needed to visualize bacteria.
Leifson stain:
For thickening the flagellum.
CV and a mordant. (wtf is that)
WHICH BACTERIA MAKE ENDOSPORES?
Gram pos. Bacillus (anthrax, insecticides) and clostridium (tetanus, botulinum, gangrene)
Endospore stain:
Visualization of endospores. Malachite green is steamed into the endospores. Counterstain with safranin.
The different kinds of stains:
Gram, acid fast, negative, leifson, endospore.
Chemical needs for growth:
CHONPS, calcium, trace elements for cofactors.
Aerobes and free radicals:
Use enzyme series to detoxify free radicals.
Catalase: 2 H2O2 -> 2 H2O + O2
Different kinds of oxygen requirement/sensitivity:
Obligate anaerobe Facultative anaerobe - prefers O2 Obligate aerobe Aerotolerant aerobe - doesn't care Microaerophile - just a lil bit of O2
Characteristics of agar:
Carbs from red algae. Melts at 85ºC, solidifies at 40ºC.
Kinds of special media:
Selective, differential
MacConkey agar:
Selects against Gram pos using salts and CV.
Differential for lactose fermentors (pos = purple).
Mannitol salt agar (MSA):
Selective with high salt concentration.
Differential for alcohol fermentation (pos = yellow).
Useful for S. aureus.
Blood agar:
Enrichment and differential.
Hemolysis - alpha (discolouration), beta (clearing), gamma (none).
Saboraud dextrose agar:
High glucose. Selective for yeasts and molds bc high sugar and acidic pH.
SIM deep:
Differential.
Sulfur reduction: pos = black.
Indole production: add Kovak, pos = pink/red
Motility
Oxidase assay:
Tests for cytochrome 3 oxidase (making ATP using O2). Pos = purple.
Enterotube II:
Biochemical identification system that does a bunch of different stains/tests at once.
Biochemical identification using DNA:
PCR - use a specific primer that only binds to certain species of DNA.
Antibody testing:
See if the unknown binds to specific antibodies.
Rapid strep test: for strep pyogenes.
Also for determining serotype/serogroup (how severe)
*** more on this later?
Plate count to CFU equation:
Observed count * (1 / volume plated) * (volume of tube) * (1/dilution factor)
Activity spectra:
Can be broad or narrow. The closer an organism is to us, the more specific a drug has to be to fight it.
Antimicrobial targets:
Inhibit cell wall, protein synthesis, metabolism, replication/translation, cell membrane
Cell wall inhibitors:
Penicillin and cephalosporins. Natural penicillin only works on gram neg. All contain beta-lactam ring. Bind and inhibit transpeptidases in the periplasmic space.
LYSIS.
Protein synthesis inhibitors:
Interfere with ribosome/mRNA/tRNA complex. Ex: chloramphenicol (broad), streptomycin (gram neg), neomycin (topical streptomycin), tetracycline (broad).
STASIS.
Side effects of protein synthesis inhibitors:
Chloramphenicol can poison mitochondria and cause anemia. Bad for babies.
Streptomycin can cause deafness.
Tetracycline can yellow developing teeth, because it’s negatively charged and binds to calcium.
Plasma membrane inhibitors:
Polymyxins damage gram neg membranes. (Toxic to neurons and kidneys.)
Daptomycin depolarizes gram pos membranes.
Polysporin: Polymyxin B and bacitracin inhibit gram pos. Good as topical, not so much otherwise.
Nucleic acid synthesis inhibitors:
Rifamycin/rifampin: best against mycobacteria (TB, leprosy). Inhibits mRNA synthesis. Highly permeable because of -OHs and hydrophobicity.
Quinolines: inhibit DNA gyrase (replication). Broad spectrum. Ex: ciprofloxin.
Metabolic inhibitors:
Sulfonamides. Completely synthetic. Used in WWII to prevent gangrene. Blocked folate, which is used to produce thymine and uracil.
Sensitivity testing:
Disk diffusion: stick them on a plate.
Epsilometer: uses a strip to determine dose.
MIC = minimal inhibitory concentration.
Misuse of antibiotics:
Not finishing prescription
Poorly chosen antibiotic
Using antibiotic against viruses
Preventative antibiotics in animal feed
Modes of resistance: ***
Drug modification/destruction
Pathway protection: false target. Body double. Meat shield.
Target alteration: prevent binding
Rapid efflux: pump it out
Alternative pathways: ex folate scavenging.
Spread of resistance:
Some are naturally resistant or less sensitive. Resistant mutations may become a plasmid.
Combining drugs:
Synergistic interactions - using more than one antibiotic decreases chance of developing resistance. Combat resistance by using a second backup that works by a different mechanism.
Multiply individual resistances.
Topoisomerase IV:
Normally pulls two linked plasmids apart. Polymyxin B inhibits Topo IV, which breaks the chromosome.
Catalase and oxidase tests:
From lab manual ***
It’s an equation for CFU and dilution or whatever:
(CFU/mL) / desired count * volume plated = 1/dilution factor
