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nicks phase 2a flaschards > microbiology > Flashcards

microbiology Flashcards

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?

A

no haemolysis- streptococcus Bovis

22
Q

what type of bacteria release endotoxins?

A

gram negative

23
Q

what type of bacteria release exotoxins?

A

gram negative and gram positive

24
Q

what is an endotoxin?

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
Q

what is an exotoxin?

A

Proteins secreted from gram positive and gram negative bacteria. They are specific and heat labile.

26
Q

how can gram-negative bacteria be sub-divided?

A

bacilli and cocci

27
Q

what are some examples of gram-negative cocci?

A

neisseria meningitidis, neisseria gonorrhoeae

28
Q

how are gram-negative bacilli divided?

A

anaerobic and aerobic

29
Q

what organisms are classes are gram-negative bacilli?

A

bacteroides- b.fragilis

30
Q

how can the aerobic gram-negative bacilli be sub-divided?

A

simple growth requirements and fastidious growth requirements

31
Q

what kind of bacteria is MacConkey agar used with?

A

gram negative bacilli

32
Q

what organisms give a positive result with MacConkey agar and what is this positive result?

A
  • lactose fermenters- e.g. escherichia coli and klebisiella pneumoniae
  • turns MacConkey agar pink
33
Q

what organisms give a negative result with MacConkey agar and what is this result?

A
  • non-lactose fermenters- salmonella typhi, shigella dysenteriae and proteus mirabilis
  • MacConkey agar appears pale
34
Q

what gram-negative aerobic bacilli have fastidious growth requirements?

A
  • parvobacteria- e.g. haemophilus influenzae, legionella pneumophilia, campylobacter jejuni
  • helicobacter pylori
35
Q

what type of organism would you stain with Zeihl Neelsen?

A

mycobacteria- TB

36
Q

what is the optochin test?

A

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
Q

what is XLD agar used for?

A
  • to differentiate salmonella and shigella
  • salmonella- red/ pink colonies and black spots
  • shigella- red/ pink colonies
38
Q

what further test can be done for the beta haemolysis streptococci?

A

lance field grouping

39
Q

what is a key difference between gram negative and gram positive bacteria?

A

presence of lipopolysaccharide on gram negative bacteria

40
Q

what type of E. coli can cause travellers diarrhoea?

A

enterotoxigenic coli

41
Q

what infections can be caused by salmonella?

A

gastroenteritis, enteric fever and bacteraemia

42
Q

what conditions is staphylococcus aureus associated with?

A
  • abscesses
  • osteomyelitis
  • toxic shock syndrome
  • food poisoning
43
Q

what infections can streptococcus pyogenes cause?

A
  • cellulitis
  • tonsillitis and pharyngitis
  • otitis media
  • scarlet fever
44
Q

what infections can streptococcus pneumoniae cause?

A

pneumonia, sinusitis, meningitis, otitis media

45
Q

what are the results of lancefield testing?

A

A: Streptococcus pyogenes
B: Streptococcus agalactiae
D: Enterococcus, Strep bovis (group D is not beta-haemolytic)

46
Q

what do mycobacteria have to be cultured on?

A

Löwenstein–Jensen medium

47
Q

if the MacConkey test shows yellow, what is present?

A

pseudomonas aeruginosa

48
Q

if the MacConkey test shows pink, what is present?

A

E.coli

49
Q

what is used to differentiate between alpha haemolytic organisms?

A
  • optochin test
  • sensitive= strep pneumoniae
  • resistant= strep viridian’s
50
Q

what is used to differentiate between beta haemolytic organisms?

A

lancefield testing

nicks phase 2a flaschards (15 decks)

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