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2a - ICS > Microbiology > Flashcards

Microbiology Flashcards

1
Q

Define a pathogen

A

Organism that causes or is capable of causing disease

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2
Q

Define a commensal

A

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

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3
Q

Define an opportunist pathogen

A

microbe that only causes disease if host defences are compromised

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4
Q

Define virulence/ pathogenicity

A

degree to which an organism is pathogenic

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5
Q

Define asymptomatic carriage

A

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

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6
Q

Describe how to apply the gram stain

A

Apply crystal violet to heat fixed bacteria
Treat with iodine
Decolourise sample with alcohol
Counterstain with safranin

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7
Q

Describe the characteristics of gram positive bacteria

A

Single membrane
Large peptidoglycan ares

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8
Q

Describe the characteristic features of gram negative bacteria

A

Double membrane
Small peptidoglycan area
Endotoxins (LPS)

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9
Q

Describe endotoxins

A

component of the outer membrane of bacteria. They are heat stable and non-specific

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10
Q

Describe exotoxins

A

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

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11
Q

Give 2 examples of gram positive cocci

A

Staphylococcus and streptococcus

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12
Q

What test can be done to distinguish between staphylococcus and streptococcus

A

Catalase test; detects presence of catalase enzyme using hydrogen peroxide
Staph = catalase +ve
Strep = catalase -ve

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13
Q

How would you describe the arrangement of Staph

A

Clusters of cocci

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14
Q

How would you describe the arrangement of Strep

A

Chains of cocci

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15
Q

What test could be done to distinguish between staph bacteria

A

Coagulase test: looks at whether a fibrin clot is formed

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16
Q

What bacteria would be coagulase positive

A

Staphylococci aureus

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17
Q

What bacteria would be coagulase negative

A

Staphylococci epidermis

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18
Q

What test could be done to distinguish between different streptococci

A

Haemolysis on blood agar; uses hydrogen peroxide o test reaction with Hb

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19
Q

What would you see on the agar plate in alpha haemolysis and give an example of a bacteria in this group

A

a-haemolysis is partial erythrocyte lysis (green colour visible)
S. pneumoniae

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20
Q

What would you see on the agar plate in ß haemolysis and give an example of a bacteria in this group

A

Complete erythrocyte lysis: you see a clear area
S. pyogenes
S. agalactiae

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21
Q

What would you see on the agar plate in gamma haemolysis and give an example of bacteria in this group

A

No haemolysis
E.g., Strep. bovis

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22
Q

Describe the appearance of bacilli

A

Rods

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23
Q

What type of organism would you stain with Ziehl Neelsen

A

Mycobacteria

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24
Q

What further test can be done for streptococci in the alpha haemolysis group?

A

Optochin test
S.pneumoniae is optochin sensitive
Virdans Strep is optochin resistant

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25
Q

Give examples of gram positive bacilli

A

Bacillus
Cornyebacterium
Listeria

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26
Q

What is MacConkey agar

A

Selective agar containing bile salts and crystal violet. If an organism ferments lactose, lactic acid will be produced and the agar will appear a pink/red colour

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27
Q

What kind of bacteria is MacConkey agar used with

A

Gram negative bacilli

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28
Q

Name 2 gram negative bacilli that will give a positive result with MacConkey agar

A

Escherichia coli
Klebsiella pneumoniae
(pink)

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29
Q

Where in the body might you find Staphylococci

A

Nose and skin

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30
Q

Name 2 gram negative bacilli that will give a negative result with MacConkey agar

A

Shigella
Salmonella
(white)

31
Q

How does serology aid to distinguish between gram negative bacilli

A

Detects the presence of the H antigen (flagella)
Salmonella is motile and have flagellum (+ve)
Shigella is non motile and doesn’t have flagellum (-ve)

32
Q

Name 2 infections associated with E. coli

A

UTIs
Traveller’s diarrhoea

33
Q

What type of bacteria are neisseria

A

Gram negative diplococci

34
Q

What are mycobacteria

A

Aerobic
Non-motile
Non spore forming
Bacilli

35
Q

Give 2 example of mycobacteria

A

M. tuberculosis (TB)
M.leprae (leprosy)

36
Q

What colour do s. aureus colonies appear on blood agar

A

Creamy/ yellow

37
Q

What is XLD agar used for

A

It is a selective growth medium used to isolate salmonella and shigella
Salmonella shows black dots

38
Q

Define antibiotics

A

Agents produced by microorganisms that kill or inhibit the growth of other microorganisms

39
Q

Name the 3 main types of beta lactams

A

Penicillin
Cephalosporins
Carbapenems

40
Q

Apart from beta lactams, what other type of antibiotic inhibits cell wall synthesis
Give examples

A

Glycopeptides
Vancomycin
Teicoplanin

41
Q

How do beta lactams inhibit cell wall synthesis

A

Disrupt peptidoglycan production by binding covalently and irreversibly to the penicillin binding site
Cell wall is disrupted and lysis occurs

42
Q

What type of bacteria are beta lactams particularly effective against and why

A

gram positive bacteria as they have thick cell walls which makes them more susceptible to ß-lactams

43
Q

Name 3 penicillin’s

A

Amoxicillin
Flucloxacillin
Benzylpenicillin

44
Q

Name 3 cephalosporins

A

Cefotaxime
Ceftriaxone
Cefuroxime

45
Q

Name 2 carbapenems

A

Meropenem
Imipenem

46
Q

Give 3 ways antibiotics inhibit nucleic acid synthesis and give examples in each group

A

Break DNA strand: Metronidazole
Bind to RNA polymerase: Rifampicin
Inhibit DNA gyrase: Quinolones (Ciprofloxacin)

47
Q

Give 2 examples of antibiotics that inhibit folate synthesis

A

Trimethoprim
Co-trimoxazole

48
Q

Why shouldn’t trimethoprim be given to pregnant women

A

Folate is important during pregnancy to prevent spina bifida

49
Q

What type of antibiotic is usually used for those with a penicillin allergy

A

Macrolides

50
Q

Name 2 types of antibiotics that prevent protein synthesis by binding to the 50S unit
Give examples for each

A

Macrolides e.g., Clarithromycin
Lincosamides e.g., Clindamycin

51
Q

What 2 types of antibiotics inhibit protein synthesis by binding to the 30S subunit. Give examples for each

A

Tetracyclines - doxycycline
Aminoglycosides - gentamicin

52
Q

What are bactericidal antibiotics

A

Antibiotics that inhibit cell wall synthesis

53
Q

Define minimum inhibitory concentration (MIC)

A

The lowest concentration of a chemical that prevents the growth of a bacterium

54
Q

What are bacteriostatic antibiotics

A

Inhibit protein synthesis, DNA replication or metabolism

55
Q

What does a drug need to ensure it inhibits metabolic processes

A

Concentration: occupy an adequate n.o binding sites
Time: occupy these binding sites for a sufficient period of time

56
Q

What is concentration dependent killing

A

Antibiotics that eradicate pathogenic bacteria by achieving high concentrations at the site of binding
Key: how high the [ ] is above MIC. [Peak] / MIC ratio

57
Q

What is time dependent killing

A

Time that [serum] remain above the MIC during the dosing period
t > MIC

58
Q

Give an example of a class of antibiotics that use [dependent] killing

A

Aminoglycosides
Quinolones

59
Q

Give examples of a class of antibiotics that uses time dependent killing

A

Beta lactams
Macrolides

60
Q

What are the 4 mechanisms of antibiotic resistance

A

Antibiotic resistance
Destroy antiobiotic

61
Q

What are the 4 mechanisms of antibiotic resistance

A

Change antibiotic target
Destroy antibiotic
Prevent antibiotic access
Remove antibiotic from bacteria

62
Q

How can the antibiotic target change

A

Bacteria change the molecular configuration of antibiotic binding site or masks it

63
Q

Give an example of a change in antibiotic target

A

Flucloxacillin is no longer able to bind to PBP of Staph

64
Q

Give an example of how an antibiotic is destroyed

A

Beta lactam ring of penicillins and cephalosporins hydrolysed by bacterial enzymes
Beta lactamase now unable to bind to PBP

65
Q

How can access to antibiotics be prevented

A

Modification of bacterial membrane porin channel, size, number and selectivity

66
Q

How can antibiotics be removed from bacteria

A

Proteins in bacterial membrane act as an export or efflux pump

67
Q

How does resistance develop

A
  1. Intrinsic: natural resistance
  2. Acquired:
    - spontaneous mutation
    - Horizontal gene transfer
68
Q

Give 3 methods of horizontal gene transfer

A

Conjugation
Transduction
Transformation

69
Q

What is a clinically important gram positive resistant bacteria

A

MRSA (methicillin resistant Staph. aureus)
Plasmid transfer resistance

70
Q

What is a clinically important gram negative bacteria

A

ESBL (extended spectrum beta lactamase)
Mutation at active site

71
Q

Give an example of a drug that can be used to inhibit beta lactamase in ESBL

A

Amoxicillin + Clavulanate = Co-Amoxiclav

72
Q

What types of bacteria does vancomycin work against

A

Gram positive only
Good for MRSA treatment

73
Q

What antibiotic might be used for s.pneumoniae

A

amoxicillin

74
Q

What antibiotic might be used for s.aureus (MSSA)

A

Flucloxacillin

2a - ICS (4 decks)

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