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2a - ICS > Microbiology > Flashcards

Microbiology Flashcards

(74 cards)

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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
Give examples of gram positive bacilli
Bacillus Cornyebacterium Listeria
26
What is MacConkey agar
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
27
What kind of bacteria is MacConkey agar used with
Gram negative bacilli
28
Name 2 gram negative bacilli that will give a positive result with MacConkey agar
Escherichia coli Klebsiella pneumoniae (pink)
29
Where in the body might you find Staphylococci
Nose and skin
30
Name 2 gram negative bacilli that will give a negative result with MacConkey agar
Shigella Salmonella (white)
31
How does serology aid to distinguish between gram negative bacilli
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
Name 2 infections associated with E. coli
UTIs Traveller's diarrhoea
33
What type of bacteria are neisseria
Gram negative diplococci
34
What are mycobacteria
Aerobic Non-motile Non spore forming Bacilli
35
Give 2 example of mycobacteria
M. tuberculosis (TB) M.leprae (leprosy)
36
What colour do s. aureus colonies appear on blood agar
Creamy/ yellow
37
What is XLD agar used for
It is a selective growth medium used to isolate salmonella and shigella Salmonella shows black dots
38
Define antibiotics
Agents produced by microorganisms that kill or inhibit the growth of other microorganisms
39
Name the 3 main types of beta lactams
Penicillin Cephalosporins Carbapenems
40
Apart from beta lactams, what other type of antibiotic inhibits cell wall synthesis Give examples
Glycopeptides Vancomycin Teicoplanin
41
How do beta lactams inhibit cell wall synthesis
Disrupt peptidoglycan production by binding covalently and irreversibly to the penicillin binding site Cell wall is disrupted and lysis occurs
42
What type of bacteria are beta lactams particularly effective against and why
gram positive bacteria as they have thick cell walls which makes them more susceptible to ß-lactams
43
Name 3 penicillin's
Amoxicillin Flucloxacillin Benzylpenicillin
44
Name 3 cephalosporins
Cefotaxime Ceftriaxone Cefuroxime
45
Name 2 carbapenems
Meropenem Imipenem
46
Give 3 ways antibiotics inhibit nucleic acid synthesis and give examples in each group
Break DNA strand: Metronidazole Bind to RNA polymerase: Rifampicin Inhibit DNA gyrase: Quinolones (Ciprofloxacin)
47
Give 2 examples of antibiotics that inhibit folate synthesis
Trimethoprim Co-trimoxazole
48
Why shouldn't trimethoprim be given to pregnant women
Folate is important during pregnancy to prevent spina bifida
49
What type of antibiotic is usually used for those with a penicillin allergy
Macrolides
50
Name 2 types of antibiotics that prevent protein synthesis by binding to the 50S unit Give examples for each
Macrolides e.g., Clarithromycin Lincosamides e.g., Clindamycin
51
What 2 types of antibiotics inhibit protein synthesis by binding to the 30S subunit. Give examples for each
Tetracyclines - doxycycline Aminoglycosides - gentamicin
52
What are bactericidal antibiotics
Antibiotics that inhibit cell wall synthesis
53
Define minimum inhibitory concentration (MIC)
The lowest concentration of a chemical that prevents the growth of a bacterium
54
What are bacteriostatic antibiotics
Inhibit protein synthesis, DNA replication or metabolism
55
What does a drug need to ensure it inhibits metabolic processes
Concentration: occupy an adequate n.o binding sites Time: occupy these binding sites for a sufficient period of time
56
What is concentration dependent killing
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
What is time dependent killing
Time that [serum] remain above the MIC during the dosing period t > MIC
58
Give an example of a class of antibiotics that use [dependent] killing
Aminoglycosides Quinolones
59
Give examples of a class of antibiotics that uses time dependent killing
Beta lactams Macrolides
60
What are the 4 mechanisms of antibiotic resistance
Antibiotic resistance Destroy antiobiotic
61
What are the 4 mechanisms of antibiotic resistance
Change antibiotic target Destroy antibiotic Prevent antibiotic access Remove antibiotic from bacteria
62
How can the antibiotic target change
Bacteria change the molecular configuration of antibiotic binding site or masks it
63
Give an example of a change in antibiotic target
Flucloxacillin is no longer able to bind to PBP of Staph
64
Give an example of how an antibiotic is destroyed
Beta lactam ring of penicillins and cephalosporins hydrolysed by bacterial enzymes Beta lactamase now unable to bind to PBP
65
How can access to antibiotics be prevented
Modification of bacterial membrane porin channel, size, number and selectivity
66
How can antibiotics be removed from bacteria
Proteins in bacterial membrane act as an export or efflux pump
67
How does resistance develop
1. Intrinsic: natural resistance 2. Acquired: - spontaneous mutation - Horizontal gene transfer
68
Give 3 methods of horizontal gene transfer
Conjugation Transduction Transformation
69
What is a clinically important gram positive resistant bacteria
MRSA (methicillin resistant Staph. aureus) Plasmid transfer resistance
70
What is a clinically important gram negative bacteria
ESBL (extended spectrum beta lactamase) Mutation at active site
71
Give an example of a drug that can be used to inhibit beta lactamase in ESBL
Amoxicillin + Clavulanate = Co-Amoxiclav
72
What types of bacteria does vancomycin work against
Gram positive only Good for MRSA treatment
73
What antibiotic might be used for s.pneumoniae
amoxicillin
74
What antibiotic might be used for s.aureus (MSSA)
Flucloxacillin

2a - ICS (4 decks)

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