Microbiology (1-8) Flashcards

Question

How does penicillin affect peptidoglycan?

Answer 1

Penicillin inhibits peptidoglycan synthesis → transpeptidation is penicillin sensitive → halts cell wall synthesis, osmotically sensitive cells lyse → more effective against gram +ve bacteria

Answer 2

Teichoic acids are found in gram +ve cell walls → covalently connected to peptidoglycans or plasma membrane → involved in making cell surface negative charged (may help acquire Mg2+ and Ca2+)

Answer 3

Archaeal cell walls don't contain peptidoglycan (not sensitive to penicillin - fine because not pathogenic) → some methanogens contain pseudomurein - beta 1,3 links instead of beta 1,4

Answer 4

Phospholipid bilayer → hydrophobic tails, hydrophilic heads → separates and protects cell from environment → hydrophilic/charged substances may attach to the hydrophilic surfaces → proteins that traverse the bilayer have hydrophobic regions

Answer 5

Sterols (eukaryotes), hopanoids (bacteria) → rigid planar molecules, stabilise membrane structure

Answer 6

Due to the insertion of lipopolysaccharide into the external layer of the outer membrane → provides defence against cytotoxic chemicals like antibiotics

Answer 7

1. Braun's lipoprotein → covalently linked to peptidoglycan and embedded in outer membrane by hydrophobic end 2. Adhesion sites → where inner and outer membrane adhere, allow transport of substances to OM and out of cell

Answer 8

(shows the 2 domains of life are different) Archaeal membranes branched chain hydrocarbons attached to glycerol by ether links rather than fatty acid-ester links → stabilised by isoprene → contain double-headed lipids which make a mono-layer - stabilises membrane at extreme temperatures

Answer 9

Large complex molecules containing lipid and carbohydrate → lipid A, core polysaccharide, O side chain When free in host called endotoxin → can induce massive immune response (septic shock)

Answer 10

Two glucosamine residues linked to fatty acids and phosphate → anchors LPS into outer membrane → remaining LPS projects out of cell surface → lipid A most immunogenic as endotoxin

Answer 11

Very specific to the species → in salmonella: glucose, galactose, heptulose x2, 2-keto-3-deoxyoctonate x3 → also referred to as R-antigen or R-polysaccharide

Answer 12

Variable region responsible for the antigenic make-up of bacteria → difference in O antigen defines receptor → different O serotypes linked to disease → lipid A and core polysaccharide straight, O side chain flexible and bent

Answer 13

1. lipid A stabilises outer membrane structure 2. core polysaccharide is charged contributing to the negative charge on surface → helps protect cell + attracts nutrients 3. charged hydrophilic external layer reduces permeability of hydrophobic substances → preventing entry of bile salts, antibiotics 4. protects against host defences 5. toxic to animals - toxicity linked to LPS lipid A (endotoxin/0 6. key diagnostic tool

Answer 14

Released by pathogens during cell division or by lysis → can act to prime immune system against pathogen if detected → LPS in the blood can cause septic shock syndrome → immunogenic even in absence of living cells tests for endotoxins: rabbit pyrogen test, limulus amoebocyte lysate (LAL) assay

Answer 15

1. heat stable 2. toxic in nanogram amounts 3. interacts with innate immune system cells → can trigger the release pf cytokines in a cascade → activates transcription factors like interferon-B and TNF 4. can result in; inflammation, fever, vasodilation, thrombosis, depletion of platelets/clotting factors (leading to haemorrhage), shock

Answer 16

Transmembrane proteins that act as channels for entrance and exit of solutes → makes the outer membrane relatively permeable to small molecules → most are non specific, some are selective → high thermal stability → resistant to protease and detergent degradation

Answer 17

16-stranded antiparallel B-barrel → exceptionally stable; extra stability from salt bridges between N- and C-termini → hourglass shape with central constriction → charges inside define size of solute that can traverse

Answer 18

Compounds diffuse through porins into periplasm → periplasm in the space between the outer and cytoplasmic membrane → gel like consistency due to abundant proteins

Answer 19

1. nutrient acquisition - hydrolytic enzymes like alkaline phosphate 2. energy conservation - electron transport proteins )produce energy) 3. some peptidoglycan synthesis enzymes 4. periplasmic binding proteins - deliver specific compounds to transporters in cytoplasmic membrane 5. chemoreceptors - involved in chemotaxis, sensing what enters

Answer 20

Long thin extracellular helical structures made of protein subunits that aid in motility → connected to a motor that spins them clock- or anti- clockwise allowing bacteria to swim → rotates at very high speeds → biological motors

Answer 21

Complex ring structures anchored into the membrane and call wall/outer membrane → rings (lL, P, S-M, & C) and hooks are rigid and attached → filament id made of a single protein called flagellin → flagellum shaft is easily removed by vigorous shaking → different antigenic properties of shaft, tip of shaft and hook → the motor is driven due to transfer of protons through the ring structure (from periplasm to cytoplasm)

Answer 22

Growth occurs at the tip → subunits made in cytoplasm are exported to periplasm and sent up the flagella → constant growth to repair damage caused by movement

Answer 23

Rotary motion provided by the basal structures → powered by proton motive force → requires lots of energy (one rotation requires translocation of 1000 protons) → changes in charge lead to conformational change of MotA, causing movement relative to MotB, second conformational change with loss of charge

Answer 24

1. no L and P rings 2. anchor in the membrane layer is more complex 3. mot proteins surround inner ring and movement of these relative to each other provides the force

Answer 25

Via flagella; motility pattern alternate between 'run' and 'tumble' → run - motor rotates anti-clockwise, flagellar filaments form bundle and propel cell → tumble - quick reversal of motor to clockwise rotation, produces twisting force that transforms flagella → separates filaments act in uncoordinated ways to generate forces that change orientation of cell - toward favourable conditions

Answer 26

1. aerotaxis - movement towards oxygen 2. chemotaxis - movement towards nutrients also away from toxins 3. magnetotaxis - movement along lines of magnetism 4. phototaxis - movement towards light

Answer 27

Bacteria sense changes in nutrient concentration in environment → methyl-accepting chemotaxis proteins (MCP) detect and interact with cytoplasmic proteins → che proteins interact with rings of motor regulating direction, dictates run or tumble by switch of rotation → CheA-p phosphorylates CheY - CheY-p binds to flagellar motor conformational change causes bacterium to tumble attractants decrease CheY-p → less switching, longer runs repellents increase CheY-p → more tumbling

Answer 28

Protein vesicles that contain gas in planktonic bacteria → confer buoyancy, allows cells to float up to oxygenated water or towards light → can be involved in vertical migration in aquatic systems q

Answer 29

Surface appendages, mediate adhesion → don't spin like flagella → involved in host-pathogen interactions, colonisation, biofilm formation, adhesion, resistance to phagocytosis, antigenic → specialised pili involved in genetic exchange between bacteria

Answer 30

They allow the cell to break mucus layer and attach to epithelial cell and invade

Answer 31

Thin surface polymer → made up of 500-3000 subunits of the protein FimA, stacked in a helical cylinder → important virulence factor in a range of pathogens (like E.coli, salmonella)

Answer 32

FimH → tip adhesion, binds to surface of target FimF & FimG → link FimH adhesin onto the fimbriae

Answer 33

FimC → chaperone protein FimD → usher protein

Answer 34

PAP: Pylonephritis-Associated-Pili → critical virulence factor of uropathogenic E. coli which can cause cystitis and pyelonephritis (UTI that reaches kindeys) → similar in structure and assembley to type I fimbriae - PapG is the tip adhesin,

Answer 35

Widely distributed in gram -ve → longer than fimbriae, only a few pili per cell, typically at both cell poles, most are not hollow unlike flagella → twitching motility - allows movement by attaching

Answer 36

1. host cell adhesion 2. biofilm formation 3. twitching motility - crawl along surface 4. enable enteropathogenic E. coli to form microcolonies on tissue monolayers → often aggregate laterally to form bundles - lack virulence

Answer 37

LPS (O antigen) and fimbriae (K antigen) e.g E. coli → CFA (colonising factor agent) fimbriae are present on E. coli pathogenic to humans but K99 and K88 are fimbiral antigens in animal pathogens

Answer 38

ETEC strains have specific interactions with mucosal epithelium depending on CFA have CFA → pathogenic, adhere to e.g. small intestine and urinary tract, express pathogenicity by producing toxins no CFA → non pathogenic, adhere to colon, routinely secreted in faeces

Answer 39

Involved in transfer of genetic information (from cell that contains F plasmid to one that doesn't) → unlike other pili/fimbriae have a central 2nm wide channel → found on many Gram -ve bacteria → all plasmid encoded

Answer 40

Transfer of genetic information via F pilus → F+ donor attaches to F- recipient via surface protein on recipient → retraction - cells brought close together → exchange - replication and transfer of plasmid → results in 2 F+ cells

Answer 41

Dormant stage in bacterial life cycle → simple, tough version of bacterial cell → form inside of a bacterial cell - when a vegetative cell becomes stressed → survival mechanism - resistant to heat, desiccation and radiation → some viable for 100,000 years → only Gram +ve produce endospores

Answer 42

Staining with malachite green → heat/steam required for dye penetration → after washing only spores will remain with the primary dye (malachite green)

Answer 43

Complex series of cellular differentiation stages forming an endospore → in response to extreme stress → each stage controlled by different gene (over 200 genes involved - evolutionarily important) → process take 8h to complete →environmental trigger stops production of normal cell growth proteins and switches to sporulation genes → trigger is probably nutrient depletion

Answer 44

0. vegetative cell under stress 1. DNA organised along cell axis 2. genome copy enclosed in forespore septum 3. cell membrane engulfs forespore in second membrane 4. cortex between membrane accumulates calcium and dipicolinic acid, becomes dehydrated to <10% → resistance to chemicals and heat increases 5. complex exosporium layers produced 6. spore matures with complete cortical layers 7. original cell lyses releasing spore

Answer 45

Many new layers, outermost exposporium - thin layer of spore-specific proteins → not essential for survival but maybe dispersal Inside core containing; genome, cytoplasm, ribosomes - metabolically inactive Small acid soluble proteins maintain genome integrity → prevent formation of pyrimidine dimers in DNA (cause DNA damage)

Answer 46

Dehydration (due to peptidoglycan cortex) of endospores prevents denaturation → can be resistant up to 150C → autoclaving destroys spores (conditions not seen in nature)

Answer 47

Low income countries → in the USA leading cause of death in 1900 - infectious disease in 2000 - heart disease and cancer → in 2016 in Africa 50% of all deaths due to infections

Answer 48

Systems designed to stop infection → lysozymes in tears and other secretions - dissolves cell walls → skin (physical barrier) produces antimicrobial fatty acids, normal flora inhibits pathogen colonisation → rapid pH changes inhibit microbial growth → flushing urinary tract prevents colonisation → mucus, cilia lining move microorganisms out of the body → blood proteins inhibit microbial growth

Answer 49

Colon (GI tract contains the most), oral cavity, vagina

Answer 50

The ecological community of commensal, symbiotic and pathogenic microorganisms that share our body space

Answer 51

Shield body tissues against invasion of pathogens Production of vitamins by bacteria

Answer 52

1. adhesion to and entry into cells 2. antiphagocytic activity, immune system evasion 3. production of toxins → conventional virulence factors; bacterial toxins, adhesins, cell surface carbohydrates and capsules, LPS

Answer 53

MRSA → Methicllin Resistant Staphylococcus aureus Limited options of antibiotic therapy left due to multiple antibiotic resistance - last choice in vancomycin Now VRSA isolates have been isolated → untreatable by any known antibiotic

Answer 54

1. beta-lactams → interrupt cell wall formation (penicillins and cephalosporins) 2. macrolides → inhibit protein synthesis (erthyomycin) 3. fluroquinolones → inhibit DNA gyrase (ciprofloxacin) 4. tetracyclins → inhibit protein synthesis (tetracycline) 5. aminoglycosides → inhibit protein synthesis (kanamycin) `

Answer 55

1. reduces permeability → penicillins 2. inactivation → penicillins, aminoglycosides 3. target alteration → macrolides 4. new resistance pathway → sulfonamides 5. efflux, tetrayclines, erthyromycin

Answer 56

In 1879 Louis Pasteur used weakened Pasteurella multocdia (chicken cholera) to infect chicken - did not cause disease → tested on sheep, no vaccinated sheep died/suffered → evidence that weakened vaccination worked

Answer 57

Tetanospasmin - released by cell lysis, spreads through blood and lymph → targets CNS, binds to peripheral nerve terminals Halts the release of glycine and GABA neurotransmitters → normally check nerve impulses → absence leads to muscular spasms

Answer 58

The vaccine targets the toxin not the organism → recovery from tetanus does not confer immunity