Microbial basics Flashcards
Molecular Koch’s postulates
Falkow - genes -> pathogenic traits
same principles
- identify gene present in sick, not present in healthy
- disruption reduces virulence
Koch’s postulates
- organism in all sick animals, not in any healthy
- isolate -> pure culture
- inoculate -> same disease
- re-isolate -> pure culture
requires infectable animal model…
requires culture growth
difficult with obligate intracellular (no culture growth)
Classes of micro-organisms
Bacteria -
- many pathogens, some photosynthetic
- rigid cell wall
- require organic energy source
Fungi
- some pathogens, non-photosynthetic
- rigid cell wall (but diff than bacteria)
Not covered in this course:
Algae - photosynthetic, no pathogens
Protozoa - some pathogens, no rigid wall, unicellular, nonphotosynthetic
(ex amoeba)
Characteristics of micro-organisms
Unicellular (but can behave collectively, communicate)
Eukaryotic - fungi, protozoa, algae
Prokaryotic - bacteria
diff chromosomes, organelles, movement, wall
Chromosomes (eukaryotic vs pro)
Eukaryotic - vary in number, mitosis
Prokaryotic
- one circular (occassionally multiple)
- segregation but no mitosis
Basics of bacterial identification
Morphology of colonies Morphology and staining of individuals - Gram stain - cocci, bacilli, etc Metabolism - ie fermentation of specific nutrient Antigens (specific assays)
PCR - used clinically for specific detection
Organelles (eukaryotic vs pro)
Eukaryotic - membrane-bound organelles
- ex mitochondria with ox-phos enzymes
Prokaryotic - no organelles
- oxidative phosphorylation on cytoplasmic membrane
Cellular movement (eukaryotic vs pro)
Eukaryotic
- cytoplasmic streaming
- cilia or flagella (9 doublets + 2 of microtubules, covered by membrane)
Prokaryotic
- no cytoplasmic streaming (too dense)
- flagella - repeating flagellin subunits in hollow tube, no membrane or microtubules
Cell wall (eukaryotic vs pro)
Eukaryotic
- plants, algae - cellulose
- fungi - chitin (acetyl glucosamine) + beta 1,3 glucan
- often have sterols in cell membrane
Prokaryotic
- peptidoglycan polymer - muramic acid, D-amino acids, etc
- key for specificity of antibiotics
Protein synthesis
Eukaryotic
- RNA splicing and transport before translation
- 80S ribosome
Prokaryotic
- simulataneous transcription and translation (no splicing)
- 70S ribosome
Bacteria shapes
Rigid cell wall - don’t change with osmotic pressure
Usu about 1 micron
“Pleomorphic” - changes shape
Cocci - round - can be elongated (Pneumococcus, Gonococcus) or perfect sphere (Staph)
Bacilli - can have variations in shape (ex coccibacilli)
Vibrio - curved (Cholera)
Spirochete - not actually rigid, spiral (ex Treponema pallidum, Borrelia burgdorferi)
Bacterial division
Binary fission -> filament if incomplete separation
Long axis -> chain - Streptococci, all bacilli Random -> cluster Stick together - Corynebacterium -> stacks - Staphylococcus
Cell membrane
Lipid bilayer No sterols (vs eukaryotic)
- oxidative enzymes (similar to inner mitochondrial)
- cell wall synthesis
- selective/active transport
- secretion of toxins
Cytoplasmic inclusions
Ribosomes (70S, antibiotic target)
Granules - nutrient storage without increased osmolarity
- high molecular weight lipid
- glycogen
- metachromatic = polymerized phosphate (ex Diptheria)
Cell wall structure
25-30% of cell weight
Glycosidic bond -> chain
- n-acetyl glucosamine (NAG)
- muramic acid (= NAG + lactic acid)
- glycosidic bond broken by lysozyme
Cross-linking - necessary for stability and rigidity
- via tetrapeptide on lactic acid (lots of variation, weird amino acids)
Gram negative structure
Thin cell wall (only peptidoglycan)
Outer membrane
- lipopolysaccharide (LPS) = antigen!
- lipid A embedded = toxin, polysaccharide attached = antigen (repeating oligosaccharide = “O” antigen)
- anchored to cell wall
- pores in outer membrane - non-specific for small (block vanco)
- generally more resistant
Periplasmic space = between cytoplasmic and outer membrane
(lots of enzymes for intake of nutrients, penicillinase)
Gram positive structure
No outer membrane
Thicker cell wall - peptidoglycan + carbohydrate polymer
- ex ribitol phosphate (sugar-OH) in Staph = teichoic acid
- polymers are antigens
Gram stain
Crystal violet + iodine -> insoluble complex
Decolorizer
- Gram negative washes out (EtOH degrades outer membrane -> thinner cell wall)
- Gram positive retained dt thick cell wall
Counterstain
Gram positive can appear negative if old (wall breakdown)
Capsule
Non-essential, polysaccharide coat Affects pathogenicity (ie resists phagocytosis) Can be antigen
Not super solid - particles floating free, detect in urine or CSF for dx
Flagella
All motility is via flagella!
10-20 nm x 8-12 microns (longer than cell)
Flagellin -> repeating polymer, hollow tube
Requires electron micrograph, special stains
Either polar or peritrichous
Movement - can have chemoreceptors for chemotaxis
- attractant (sugar, aminos) -> counter-clockwise spin -> straight line
- repellant -> clockwise spin -> “tumble”
Pili
aka fimbrae (interchangeable)
Adhesion (almost all bacteria have some form)
- recognize and bind to sugars on mammalian cells
- not sole mechanism (ex Gram + glycocalyx, Gram (-) adhesins in outer membrane)
Examples
- F pili - “donor” bacteria during conjugation
- type IV - push and pull across surface -> twitching motility, aggregation
- Gonococcus - adheres to epithelial cells
Sporulation
Stimulus (nutrient deprivation) ->
Sporulation (forms within bacillus - characteristic location and shape) ->
Spore can persist for long periods, resistant to boiling, drying, chemicals, staining (low H2O content, protein coat) ->
Germinate to vegetative in favorable conditions
Ex:
- Bacillus anthracis -> lungs
- Clostridium tetani - soil -> wounds
