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nicks phase 2a flaschards > microbiology > Flashcards

microbiology Flashcards

(50 cards)

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1
Q

what is a pathogen?

A

organism that causes or is capable of causing disease

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2
Q

what is a commensal?

A

organism which colonises the host but causes no disease in normal circumstances

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3
Q

what is an opportunist pathogen?

A

microbe that only causes disease if host defences are compromised

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4
Q

what is virulence?

A

the degree to which a given organism is pathogenic

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5
Q

what is asymptomatic carriage?

A

when a pathogen is carried harmlessly at a tissue site where it causes no disease

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6
Q

how is gram staining done?

A
  1. Application of crystal violet- stains all bacteria purple
  2. Iodine is added- traps crystal violet within peptidoglycan layer
  3. Samples washed w/ acetone
  4. In gram negative cells, the acetone destroys the lipopolysaccharide- so the stain washes out and returns to its normal colour
  5. GRAM POSITIVE STAY PURPLE AS THE CRYSTAL VIOLET DOES NOT WASH OUT OF THEM
  6. Counter stain added- stains gram negative cells pink
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7
Q

what are the differences in the structures of gram positive and gram negative bacteria?

A
  • Gram positive have (from inside to out), a phospholipid bilayer then a tick peptidoglycan wall
  • Gram negative have a phospholipid bilayer, then a thin peptidoglycan wall, then an outer membrane, then thick lipopolysaccharides- composed of lipid A, O antigen and terminal sugars

both are surrounded by a capsule

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8
Q

what can gram-positive bacteria be divided into?

A

bacilli and cocci

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9
Q

how are the gram-positive bacilli divided?

A

aerobic and anaerobic

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10
Q

what are some examples of aerobic gram-positive bacilli?

A

listeria monocytogenes, cornybacterium diptheriae

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11
Q

what are some examples of anaerobic gram-positive bacilli?

A

clostridium tetani, clostridum dificile

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12
Q

how can gram-positive cocci be subdivided and what are the results?

A
  • catalase test
  • staphylococcus- positive
  • streptococcus- negative
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13
Q

how do streptococcus appear down a microscope?

A

chains of cocci

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14
Q

how do staphylococcus appear down a microscope?

A

clusters of cocci

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15
Q

what test can be done to differentiate between the types of staphylococcus?

A

coagulase test

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16
Q

what does a positive coagulase test indicate?

A

staphylococcus aureus

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17
Q

what does a negative coagulase test indicate?

A

staphylococcus epidermidis

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18
Q

how can streptococci be differentiated?

A

blood-agar haemolysis

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19
Q

what does an Alpha haemolysis show?

A

appears green- streptococcus pneumoniae or strep viridian’s

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20
Q

what does beta haemolysis show?

A

appears clear- streptococcus pyogenes or strep aglalactiae

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21
Q

what does gamma haemolysis show?

Study These Flashcards
A

no haemolysis- streptococcus Bovis

22
Q

what type of bacteria release endotoxins?

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A

gram negative

23
Q

what type of bacteria release exotoxins?

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A

gram negative and gram positive

24
Q

what is an endotoxin?

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A

Endotoxin (LPS) is an outer membrane component released when bacteria are damaged. They are less specific and are toxic to the host. They are heat stable.

25
what is an exotoxin?
Proteins secreted from gram positive and gram negative bacteria. They are specific and heat labile.
26
how can gram-negative bacteria be sub-divided?
bacilli and cocci
27
what are some examples of gram-negative cocci?
neisseria meningitidis, neisseria gonorrhoeae
28
how are gram-negative bacilli divided?
anaerobic and aerobic
29
what organisms are classes are gram-negative bacilli?
bacteroides- b.fragilis
30
how can the aerobic gram-negative bacilli be sub-divided?
simple growth requirements and fastidious growth requirements
31
what kind of bacteria is MacConkey agar used with?
gram negative bacilli
32
what organisms give a positive result with MacConkey agar and what is this positive result?
- lactose fermenters- e.g. escherichia coli and klebisiella pneumoniae - turns MacConkey agar pink
33
what organisms give a negative result with MacConkey agar and what is this result?
- non-lactose fermenters- salmonella typhi, shigella dysenteriae and proteus mirabilis - MacConkey agar appears pale
34
what gram-negative aerobic bacilli have fastidious growth requirements?
- parvobacteria- e.g. haemophilus influenzae, legionella pneumophilia, campylobacter jejuni - helicobacter pylori
35
what type of organism would you stain with Zeihl Neelsen?
mycobacteria- TB
36
what is the optochin test?
differentiates between alpha haemolytic streptococci- streptococcus pneumoniae gives a positive result as it is sensitive to optochin- clear zone around disc - all other alpha haemolytic streptococci (e.g. viridans streptococci) is resistant so there will be growth around disc
37
what is XLD agar used for?
- to differentiate salmonella and shigella - salmonella- red/ pink colonies and black spots - shigella- red/ pink colonies
38
what further test can be done for the beta haemolysis streptococci?
lance field grouping
39
what is a key difference between gram negative and gram positive bacteria?
presence of lipopolysaccharide on gram negative bacteria
40
what type of E. coli can cause travellers diarrhoea?
enterotoxigenic coli
41
what infections can be caused by salmonella?
gastroenteritis, enteric fever and bacteraemia
42
what conditions is staphylococcus aureus associated with?
- abscesses - osteomyelitis - toxic shock syndrome - food poisoning
43
what infections can streptococcus pyogenes cause?
- cellulitis - tonsillitis and pharyngitis - otitis media - scarlet fever
44
what infections can streptococcus pneumoniae cause?
pneumonia, sinusitis, meningitis, otitis media
45
what are the results of lancefield testing?
A: Streptococcus pyogenes B: Streptococcus agalactiae D: Enterococcus, Strep bovis (group D is not beta-haemolytic)
46
what do mycobacteria have to be cultured on?
Löwenstein–Jensen medium
47
if the MacConkey test shows yellow, what is present?
pseudomonas aeruginosa
48
if the MacConkey test shows pink, what is present?
E.coli
49
what is used to differentiate between alpha haemolytic organisms?
- optochin test - sensitive= strep pneumoniae - resistant= strep viridian's
50
what is used to differentiate between beta haemolytic organisms?
lancefield testing

nicks phase 2a flaschards (15 decks)

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