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Y2 Clinical Pathology > Antibiotics > Flashcards

Antibiotics Flashcards

1
Q

How are bacteria classified?

A

They are stained and looked at

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2
Q

What is the difference in structure between a gram positive and gram negative bacteria?

A

Gram positive:

  • has a peptidoglycan cell wall
  • stains purple with gram stain

Gram negative:

  • the outermost layer is the outer cell membrane
  • the cell wall is protected in the middle
  • stains pink with gram stain
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3
Q

What are the 2 shapes of bacteria?

A

Cocci:

  • these are round in shape
  • in pairs, chains or groups

Rods:

  • these are elongated
  • in groups, chains or solo
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4
Q

Complete the table showing the results of the Gram stain and further tests

A
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5
Q

WHy is the catalase test used?

A

To distinguish between staphylococcus and streptococcus

these are both gram positive cocci

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6
Q

How do b-lactams work?

A

B-lactams are a group of antibiotics which all contain the b-lactam group

they are cell wall synthesis inhibitors

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7
Q

What are the 4 types of b-lactams?

A

Penicillins:

  • amoxicillin
  • penicillin V

Cephalosporin:

  • cefuroxime

Carbapenem:

  • Meropenem

Glycopeptides:

  • vancomycin
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8
Q

What are the 4 antibiotics which interfere with translation (protein synthesis)?

A
  1. Tetracyclin (doxycycline)
  2. Macrolides (erythromycin)
  3. Chloramphenicol
  4. Aminoglycosides (gentamycin)

The shape and composition of the bacterial ribosome is different so it can be exploited through antibiotic use

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9
Q

Which antibiotic interferes with RNA synthesis?

A

Rifamycin (rifampicin)

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10
Q

Which antibiotics interfere with DNA replication?

A

Quinolones:

  • ciprofloxacin

Metronidazole

  • used in anaerobic infections

Anti-folates:

  • trimethoprim
  • sulfadrugs
  • folate is needed for nucleotide synthesis, so bacteria are prevented from making DNA
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11
Q

What are the 4 mechanisms of drug resistance?

A
  1. Drug inactivation or modification
  2. Alteration of target or binding site
  3. Alteration of metabolic pathway
  4. Reduced drug accumulation
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12
Q

How does “drug inactivation or modification” work as a mechanism of resistance?

A

Bacteria produce an enzyme that will break down the antibiotic

staphylococcus aureus produces penicillinase

e. Coli produces carbapenemase

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13
Q

How does “alteration of target” work as a mechanism of resistance?

A

Antibiotics have to bind to something (e.g. cell wall, ribosome)

bacteria may have evolved a binding site that is different so that the antibiotic can no longer bind to its target site

staphylococcus aureus alters the penicillin binding protein

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14
Q

How does “alteration of metabolic pathway” work as a mechanism of drug resistance?

A

Sulfa-resistant bugs can use pre-formed folic acid

e.g. Trimethoprim inhibits the folate pathway of bacteria

enterococcus will use folate from the blood surrounding it instead

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15
Q

How does “reduced drug accumulation” work as a mechanism of drug resistance?

A

This involves actively pumping out the antibiotic that is penetrating into the cell

“efflux pump”

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16
Q

Which types of bacteria are resistant to amoxicillin?

Which infections is it used against?

A
  • Most beta lactams have some gram positive and gram negative activity
  • amoxicillin is used for ENT, respiratory and urinary infections
  • bacteria with B-lactamase will break down B-lactams
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17
Q

What is used to overcome bacteria that produce B-lactamase?

A

Co-amoxiclav

this is a combination of amoxicillin and clavulanic acid

it is used against beta-lactamase producing bacteria

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18
Q

How does flucloxacillin work?

What types of bacteria are they used against?

A

It inhibits cell wall synthesis and binds to penicillin binding protein

it is mainly used to treat staphylococcus aureus infections

it is only active against gram positive bacteria

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19
Q

What does MRSA stand for?

Why is it resistant to flucloxacillin?

A

Methicillin resistant S aureus

it has a mutation in the penicillin binding protein so is resistant flucloxacillin

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20
Q

What is the difference between MRSA and staphylococcus aureus?

A

It has an extra resistant disease that gives resistance to methicillin

This means that beta-lactams can’t be used to treat MRSA

another antibiotic class needs to be used (vancomycin)

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21
Q

What is the antibiotic treatment for community acquired pneumonia?

How is this worked out?

A

Use the CURB65 score

confusion, urea >7, respiration > 30, BP < 90/60, age > 65

in LOW risk pneumonia - amoxicillin

in HIGH risk pneumonia - co-amoxiclav + clarithromycin

22
Q

What is shown on the blood culture?

A

Gram positive coccus - diplococci

this is streptococcus pneumoniae

23
Q

What is the most common cause of community acquired pneumonia?

A

Streptococcus pneumoniae

klebsiella and other gram negative bacteria are commoner in hospital acquired pneumonia

24
Q

What is the best treatment for community acquired penicillin caused by streptococcus pneumoniae?

A

Streptococcus pneumoniae is sensitive to penicillin

this has fewer side effects compared to co-amoxicillin and clarithromycin

these are broader spectrum antibiotics

25
Q

Why should a broad spectrum antibiotic not be used in long term?

A

Broad spectrum antibiotics cover a wide range of bacteria, some of which are not causing a problem

the best treatment is the most targeted treatment as you only want to kill the bacteria that is causing the problem

26
Q

What bacteria is shown here?

How is infection often contracted?

A

Clostridium difficile

a long course of broad spectrum antibiotic wipes out all the “good” bacteria

C. Difficile will overcrowd the gut as there is less competition

27
Q

How is C. Difficile infection contracted?

A
  • Gut flora contains many bacteria
  • these are all in competition with each other
  • broad spectrum antibiotics destroy a majority of species allowing a few to overgrow
  • clostridium difficile is a toxin producer - colitis
28
Q

What are the worst antibiotics for inducing C. Difficile infection?

A

Ciprofloxacin, cerfuroxime, co-amoxiclav

worse in elderly patients

29
Q

How is C. Difficile infection treated?

A

Stop current antibiotics (broad spectrum) and start oral metronidazole

30
Q

What is the difference in symptoms for an upper and lower urinary tract infection?

A

Upper urinary tract infection:

  • fever
  • loin pain
  • tachycardia
  • low blood pressure

Lower urinary tract infection:

  • dysuria
  • frequency
31
Q

What drugs are used to treat upper and lower urinary tract infections?

A

Upper urinary tract infections:

  • IV cerfuroxime

Lower urinary tract infections:

  • nitrofurantoin
  • trimethoprim
  • pivmecillnam
32
Q

What bacteria commonly cause UTIs?

A

70% of all UTIs are caused by E. coli

33
Q

What is shown here?

A

Gram negative coccus

It is meningitis caused by Neisseria meningitides

34
Q

What is the treatment for meningitis caused Neisseria meningitides?

A

IV ceftriaxone

35
Q

What is meningitis?

What is it caused by?

A

It is an infection of the meninges

In children and young adults it is caused by N. Meningitides

In elderly patients it is caused by Streptococcus pneumoniae

It was previously also caused by Haemophilus influenza, but this is now vaccinated

36
Q

What is the difference between meningitis and meningococcal septicaemia?

A

Meningitis affects the CNS only

Meningococcal septicaemia is a CNS and bloodstream infection

37
Q

What is the definition of systemic inflammatory response syndrome (SIRS)?

A

2 of the following must be present:

  • temperature > 38
  • heart rate > 90
  • resp rate > 20
  • White blood cells > 12
38
Q

What is the definition of sepsis?

A

SIRS and a suspected focus of infection

39
Q

What is the definition of septic shock?

A

Sepsis and a low blood pressure ( < 90 / 60 )

40
Q

What technique is used in the management of sepsis?

A

BUFALO

Blood cultures:

  • 2 sets should be taken

Urine output:

  • catheterise to measure

Fluids:

  • 500 ml IV saline over 15 minutes
  • aim for 30 ml/kg in 1 hour

Antibiotics:

  • start with a broad spectrum antibiotic until you know what is causing the infection
  • then use as per suspected infection

Lactate:

  • arterial blood gas for lactate and pH

Oxygen:

  • 15 l/min via reservoir face mask
41
Q

What is cellulitis?

What is it caused by?

A

It is a skin and soft tissue infection

It is caused by gram positive cocci - staphylococcus aureus AND streptococcus pyogenes

S. Aureus is found on the skin and doesn’t usually cause problems, but trauma to the skin can lead to the bacteria entering the tissue and causing an infection there

42
Q

What is the treatment for cellulitis?

A

Flucoloxacilln

43
Q

What can happen if cellulitis is left untreated?

What causes this infection?

A

Necrotising fasciitis

this is a severe skin and soft tissue infection caused by a polymicrobial mix

it usually involves streptococcus pyogenes, which is a potent pathogen

44
Q

What is the treatment for necrotising fasciitis?

A

1 - debridement:

  • ​this involves cutting away dead skin
  • dead skin is not penetrated by antibiotics as there is no blood flowing through it

2 - meropenem + clindamycin

45
Q

What is shown here?

What condition is it associated with?

A

Splinter haemorrhages

associated with infective endocarditis

small emboli break away from the heart valves and lodge in small capillaries

46
Q

What is infective endocarditis?

What is it caused by?

A

It is an infection of the heart valves

it can be caused by many bacteria but mainly:

  1. Staphylococcus aureus
  2. Streptococci
47
Q

What is the treatment for infective endocarditis?

A

6 week IV antibiotics, depending on the cause

it is difficult to remove the bacteria from the heart valves as they form a biofilm

48
Q

What is shown on this image?

What predispositions could make someone more susceptible?

A

Brain abscess

  1. Immunosuppression
  2. HIV
  3. Intravenous drug use
  4. Endocarditis
49
Q

What are the most common bacteria that cause brain abscess?

What is the treatment?

A

Staphylococcus aureus and streps

but it can be caused by anything

it is treated with drainage and antibiotics for 4 weeks, depending on the bug

50
Q

What are the most well tolerated antibiotics in pregnancy?

A

Beta-lactams

these are the most well tolerated antibiotics and safe in pregnancy

penicillins, cephalosporins, meropenem

51
Q

Which 3 antibiotics should be avoided in pregnancy and why?

A

Quinolones:

  • e.g. ciprofloxacin
  • they cause damage to cartilage

Trimethoprim:

  • this is a folic acid antagonist

Tetracyclins:

  • depositis and stains bones and teeth

Y2 Clinical Pathology (76 decks)

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