wk 2

Question 1

explain microbial adherence

Answer 1

-after gaining entry, microbes attach to establish infection
-adhesions (pili/frimbriae or sticky) enable attachment
-also may bind to specific membrane receptors

• b.pseudomallei- glandular tissue, adenovirus- respiratory cells, e.coli- bladder + gut

Question 2

innate vs adaptive immunity

Answer 2

-innate: already there, working all the time, not specific, e.g. skin + mucous membrane

-adaptive: specific, finely tuned, created from memory of 1st attack, e.g. antibody + cell mediated immunity

Question 3

explain microbial evasion

Answer 3

• uses capsule (masks receptors on surface + prevents phagocyte adhesion)
• cell wall
  -antidigestion/killing substances that interfere with phagocytic function
  -produce catalase- causes breakdown of enzymes inside phagocyte
  -concealment (hiding from immune mechanism, infected cells signal when infected)
• immunosuppression of host (deletes capacity of hosts immune response e.g. HIV, so not able to mount a specific immune response, it predisposes host to opportunistic infections, other microbes secrete enzymes that attack immune product

Question 4

explain antigenic variation, antigenic drift + antigenic shift

Answer 4

-antigenic variaiton: tricking immune mechanism, changes antigen structure so memory cells not stimulated

antigenic drift: slight variation in coding of immunologically important antigens, reduce effectiveness of memory over time (e.g. influenza + rhinovirus)

-antigenic shift: 2 strains infect, recombined to create a new strain

Question 6

explain microbial tissue destruction

Answer 6

uses
-toxins: substances that can be secreted + part of microbes
-may damage cells/ change function
-2 types of toxins
-exotoxins (secreted into environment)
- endotoxins (part of bacterial cell, released on cell destruction)
- physical desrtuction/cell invasion (e.g. malaria + plasmodium spp)

Question 7

explain exotoxins

Answer 7

• exotoxins most potent substance on earth, e.g. gas gangrene, alpha, released by alpha toxin causes lyses of cells
  -types
  
  • haemolysin: breaks down red cells
  • leukocidins: kills white cells
• spread aided by enzymes that breakdown connective tissue
  -can change function (e.g. vibrio cholera)

Question 8

explain endotoxins

Answer 8

• part of gram neg. cell wall
  -stimulates host cell response via inflammation
  -overload host
  -increased vessel permeability + dilation
  -causes loss of fluid + septic shock

Question 9

infectious diseases depend on 2 things

Answer 9

1. itnegrity of host defense mechanism
2. virulence of mcirobes

Question 10

why is identifying pathogens advantageous

Answer 10

• track outbreaks
• develop treatment strategies
  -understanding mechanisms of infectious disease

Question 11

define serology

Answer 11

-detection of antibodies produced against a known pathogen + detection of antigen during infection

Question 12

define molecular biology

Answer 12

-detection of microbial genome + usefule for difficult or non-cultivatable microbes

Question 13

steps for IDing bacteria

Answer 13

1. initial isolation + description of colonial morpology
2. microscopic cellular morphology (refer to image 3) environmental requirements for growth (aerobic, anerobic, canophilic- requires CO2, microaerophilic- requires less O2 than air)
3. nutritional requirements + ability to utilise carbohydrates
4. phenotypic : antimicrobial susceptibility (single drug resistance) + antigenic properties (used to ID streptococcus + salmonella) + appearance of secondary differential or selective media
5. genotype: used depending on cost + availability of tech, looks at DNA base composition ratio + genomic sequencing

Question 14

possible shapes, edges, and elevations of bacterial colonies

Answer 14

-shape: round, irregular, filamentous, rhizoid, curled

-edges: entire, filamentous, undulate, lobate

-elevation: raised, flat, convex, umbonate, growth into medium

Question 15

seperate gram pos + gram neg.

Answer 15

refer to image 4

Question 16

4 types of microscopy

Answer 16

-bright field
-flyorescence
-dark field
-electron

Question 17

2 groups that bacteria can be seperated into based on needs

Answer 17

-fastidious: complex needs
-non-fastidious: common, simple cultivation, needs selection + differentiation to aid isolation

Question 18

3 classifications of media

Answer 18

-supportive: general media, non-specific growth requirements, often used as a primary media to ensure growth (e.g. nutrient agar + blood agar)

-selective: contains inhibitors that select out bacteria from a mix, e.g. antibiotics, salts, acids etc., (e.g. macConkey agar- bile salts prevents growth of most GP)

-differential: enables certain colonial characteristics (e.g. manitol salt agar- if manitol is fermented, acid produced and colour changes)

Question 19

explain sheep/horse blood agar

Answer 19

-most commonly used primary agar for clinical samples
- sues trptones, soybean protein, salt, 5% sheep blood (note: beta haemolysis = clear, alpha = greenish, gamma = none)

Question 20

explain macConkey agar

Answer 20

• used as a primary plate for first line differentiation + selectivity of GNB
  -selective- bile salts + crustal violet
  -differential- lactose + neutral red (lactose fermentators pink)

Question 21

explain primary vs secondary tests

Answer 21

-primary: used to describe genera, e.g. grams tain, acid fastness, motility, catalse, oxidase

-secondary: collection of other more specific tests used to aid in speciation

Question 22

explain catalse test

Answer 22

-enzyme detoxifies H2O2 producing bubbles + water
-used to differentiate staph + strep

Question 23

explain oxidase

Answer 23

-presence indicativ eof cytochrome oxidase system
-pos. reaction reflexts ability of microorganism to oxidise aromatic amines producing coloured end products
-most fermenters are xoidase neg. (vibirio + aeromonas as exceptions)
-most non-fermenters are oxidase psotivie (e.g. pseudomonas)
-any metal with iron will produce reaction

Question 24

explain urease

Answer 24

-secondary test
-tests bacterias ability to hydrolyse urea into ammonia, water, + CO2
-urea containing media with pH indicator
-increase pH = colour change to pink (useful for proteus (pos) + salmonella (neg.))

Question 25

explain coagulase

Answer 25

-secondary test
-tests ability of bacteria to coagulate
-e.g. S.aureus (pos. ) + S. epidermidis (neg.)

Question 26

explain indole

Answer 26

-tests ability of bacteria to produce tryptophase by product of degradation of tryptophan into indole
-useful for e.coli (pos.)

Question 27

explain methyl red

Answer 27

-secondary test
-tests ability of bacteria to produce strong mixed acid fermentation by products (pH less then 4.4.)
- red = pos., yellow = neg., organce = need to reincubate
e.g. e.coli (pos)

Question 28

explain voges proskauer reaction

Answer 28

-done on same tube after methyl red
-checks for ability to fermentation

Question 29

explain citrate

Answer 29

-secondary test
- refers to ability of bacteria to utilise citrate as sole carbon source + ammonium as sole nitrogen source
-products are alkaline
e.g. klebsiella pneumoniae (pos.), e.coli (neg.)

Question 30

6 reporting groups for CLS tests

Answer 30

Gp A: routine inclusion

Gp B: important drugs, reported selectively, source of infection

Gp C: used for testing drugs required for resistant strains or if allergy precludes Gp A or B

Gp U: drugs for urine conc.

Gp O: broad group that can be used clinicially but not for routine use

Gp Inv.: investigational, not approved for clinical use

Question 31

infection control techniques

Answer 31

cleaning: mcirobes require organic compounds, heat + water

detergent: solvent for organic materials, for sites tha tmay harbour microbes

sterilsiaiton: complete elimination of life, but no degree of sterility

microbe killing targets: proteins (for structure + function), nucleic acid (required for reproduction), cell wall (required to maintain internal environment)

Question 32

explain dry heat, radiation, and filtration

Answer 32

dry heat: 160 degree celsius for 60mins, oxidation, limited to objects with high temp. tolerance

radiation: disruption of DNA, used for heat sensitive equipment, disposable equipment

filtration: heat sensitive solutions

Question 33

explain sterilisation with ethylene oxide gas, glutaraldehyde, hydrogen peroxide

Answer 33

ethylene oxide gas: disrupts sulphydryl groups of proteins, highly toxic with good penetration, industrial application

glutaraldehyde: denatures proteins, non-corrosive, used on heat sensitive metallic equipment, toxic + allergenic (use is discouraged)

hydrogen peroxide: H2O2 vapour exposed to radio waves at 45 degree celsius, xoidising sterilant, non toxic + low temp.

Question 34

3 types of disinfection

Answer 34

-physical (heat, UV radiation, filtration), chemical, antiseptic (is used on skin)