Bacteriology - General structure & AMR Flashcards

1
Q

What are the main methods of antibiotic actions?

A
  • Inhibition of cell wall synthesis
  • Inhibition of protein synthesis
  • Inhibition of nucleic acid synthesis
  • Anti-metabolites
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2
Q

How many AMR be mediated?

A
  • chromosome-mediated
  • plasmid-mediated
  • transposon-mediated
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3
Q

Describe chromosome-mediated resistance

A
  • due to mutation in gene that codes for the target of the drug, or the transport system in the membrane that controls uptake
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4
Q

Why is plasmid-mediated resistance clinically important?

A
  • occurs in many different species
  • plasmids frequently mediate resistance to multiple drugs
    plasmids have a high rate of transfer
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5
Q

What are transposons?

A

Genes that are transferred either within or between larger pieces of DNA, such as the bacterial chromosome, and plasmids

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6
Q

What is a typical drug-resistance transposon composed of?

A

3 genes, flanked by shorter pieces of DNA - the genes code for…

  • transposase (enzyme that catalyses the excision and reintegration of the transposon)
  • a repressor that regulates synthesis of the transposase
  • the drug resistance gene
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7
Q

What is vertical gene transfer?

A

Occurs through replication

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8
Q

What are the three methods of HGT?

A
  1. Conjugation
  2. Transduction
  3. Transformation
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9
Q

What is conjugation?

A

between two bacterial cells in direct contact

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10
Q

What is transduction?

A

Injection of foreign DA into the host bacterium by a bacteriophage virus

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11
Q

What is transformation?

A

Uptake of naked genetic material fragments through cell membranes, recombined with bacterial chromosome of the recipient

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12
Q

The transfer of antibiotic resistance genes from one strain of bacterium to another via a virus is called

A

transduction

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13
Q

The transfer of antibiotic resistance genes from one strain of bacterium to another via uptake of nakedDNA is called

A

transformation

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14
Q

What are the five main mechanisms that mediate bacterial resistance to drugs?

A

1 - production of enzymes that inactivate the drug
2 - synthesis of modified targets against which the drug has reduced effect
3- reducing permeability to the drug such that an effective intracellular concentration of the drug is not achieved
4 - actively export drugs using a ‘multidrug resistance’ pump which imports proteins in exchange for a variety of foreign molecules, including antibiotics
5 - target amplification

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15
Q

What are the major categories of antibiotics?

A
  • cell wall inhibitors
  • protein synthesis inhibitors
  • nucleic acid synthesis inhibitors
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16
Q

What are the main types of cell wall inhibitors

A
  • beta lactams
  • vancomycin
  • isoniazid
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17
Q

Give examples of beta lactams

A
  • penicillin
  • amoxicillin
  • benzylpenicillin
  • flucloxacillin
  • cephalosporins
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18
Q

How do beta lactams work?

A

They irreversibly inhibit transpeptidase, causing osmotic rupture of the bacteria

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19
Q

How does vancomycin work?

A

Prevents transpeptidase from binding and catalysing cross-link formation

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20
Q

How does isoniazid work?

A

Inhibits synthesis of long chain mycolic acids required for bacterial wall and capsule

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21
Q

The most common mechanism of resistance to penicillin and cephalosporin antibiotics found inantibiotic resistant strains of bacteria is

A

beta-lactamases (but also altered penicillin-binding proteins and decreased permeability via GNB efflux)

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22
Q

What two classes of antibiotic affect the 30S subunit?

A

Aminoglycosides

Tetracyclines

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23
Q

What do aminoglycosides do?

A

Bind to 30S so it cannot bind with 50S and an mRNA for form the initiation complex

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24
Q

What do tetracyclines do?

A

Bind to 30S, preventing aminoacyl-tRNAs from entering the donor site in the ribosome

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25
Q

Example of aminoglycosides

A

streptomycin
gentamycin
tetracycline

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26
Q

Example of tetracycline antibiotic

A

Doxycycline

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27
Q

What two classed of antibiotic act in the 50S subunit?

A

Chloramphenicol

Macrolides

28
Q

What does chloramphenicol do?

A

Binds to 50S and prevents peptidyltransferase

29
Q

What do macrolides do?

A

Bind to 50S and prevent release of uncharged tRNA so donor site remains occupied

30
Q

Example of macrolide

A

Erythromycin

31
Q

Whichantibiotic is limited in use by resistance caused by increased drug efflux and changes to thehigh affinity binding site on the 70S ribosomal subunit?

A

Erythromycin

32
Q

What does MRSA stand for?

A

Methicillin-resistant Staphylococcus aureus

33
Q

What are the different classes of nucleic acid synthesis inhibitors?

A

Folic acid synthesis inhibitors
Gyrase inhibitors
transcription inhibitors

34
Q

Examples of folic acid synthesis inhibitors

A

Sulfonamides and trimethoprim (which is a 2,4-diaminopyridine)

35
Q

Examples of gyrase inhibitors

A

Quinolones → ciproflaxacin

36
Q

Example of transcription inhibition

A

Rifamycin → RNA pol inhibitor

37
Q

Which antibiotic is unique to mycobacteria?

A

Isoniazid

38
Q

Are sulphonamides (antifolates) commonly used?

A

No, because of resistence

39
Q

What are colonies usually measured in?

A

mm

40
Q

Typical size of a bacterium

A

1 micrometer

41
Q

What is a nucleoid?

A

Found in bacteria

Nucleus that lacks a nuclear membrane

42
Q

What is peptidoglycan composed of?

A

N-acetylglucosamine

N-acetylmuramic acid

43
Q

Describe Gram positive bacteria

A

Thick cell wall containing lipoteichoic acid and an inner cell membrane

44
Q

Describe Gram negative bacteria

A

Have a phospholipid outer cell envelope containing a high concentration of polysaccharide and protein, thin cell wall and inner cell membrane

45
Q

What do flagella aid?

A

Motility

46
Q

What do fimbriae aid?

A

Adherence

47
Q

How many base pairs in bacterial genome?

A

1-6million

48
Q

How many base pairs are plasmids?

A

0.1Mbps

49
Q

What are the physical methods of treating bacterial infection?

A
  • Surgical draining e.g. of abscesses

- Debridement (removal of damaged tissue or foreign objects from a wound) e.g. in necrotising fasciitis

50
Q

Example of mechanism of aminoglycoside resistance

A

Phosphotransferases

51
Q

Example of cell wall impermeability leading to AMR

A

mutant porins in Gm-neg bacteria

52
Q

What does gyrase do?

A

Required for negative supercoiling of bacterial DNA

53
Q

How many secretion systems have been identified?

A

7

54
Q

What body compartments are normally sterile?

A

Blood, lymph and CSF

55
Q

What is pasteurisation?

A

Process in which packaged and non-packaged foods are treated with mild heat to eliminate pathogens and extend shelf life

56
Q

What is autoclaving?

A

Method of sterilisation that uses high-pressure steam

57
Q

What can be used for sterilisation and disinfection?

A
Pasteurization
Autoclaving
Hypochlorite
Halogenated phenols
Gamma-irradiation
58
Q

What is peptidoglycan made up of?

A

Polymer of NAG (N-acetylglucosamine) and NAM (N-acetylmuramic acid)

59
Q

What do lipoteichoic acids do?

A

Serve a chelating agents, and also types of adherance

60
Q

What sort of environments are G+ bacteria more likely to survive? Why?

A

Dry environments, e.g. the skin, due to thick peptidoglycan layer

61
Q

What sort of environments are G- bacteria more likely to survive in?

A

Places such as the gut

Surface is hydrophilic but lipid components give hydrophobic character as well

62
Q

Does the cell surface of G- or G+ permit spore formation? Give two examples of genuses this occurs in?

A

Positive

Bacillus and Clostridium

63
Q

How may antibiotic resistance occur in G- bacteria?

A

They have outer memvranes with hydrophobic lipid bilayers and porins with size exclusion properties
Only small hydrophilic antibiotics can pass
Resistance can be caused by loss of function change of porins

64
Q

Which antibiotics are hydrophobic and can diffuse across the bilayer?

A

Aminoglycosides
Macrolides
Rifamycins

65
Q

Which type of bacteria utilise secretion systems? Why can only this type use secretion systems?

A

Gram -

Because of their outer membrane

66
Q

Which type of bacteria produces OMVs? What do OMVs do?

A

Gram negative

Allow communication of bacteria with each other, other microorganisms and the host