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Clinical Pathology > Theme 3 Lecture 17, 19, 20: Pathogen-antibiotic matching > Flashcards

Theme 3 Lecture 17, 19, 20: Pathogen-antibiotic matching Flashcards

1
Q

Why do gram-positive bacteria stain dark purple?

A

because the carbohydrate rich cell wall on outside takes up purple dye

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2
Q

Why do gram negative bacteria stain pink?

A

because the outer cell membrane prevents the dye from penetrating the peptidoglycan

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3
Q

Other than gram stain, how else can we classify bacteria?

A

by shape:

  1. cocci - in pairs, chains or groups
  2. bacilli (rods) - in chains, groups or solo
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4
Q

what is the shape of streptococci?

A

chains of cocci e.g strep pneumoniae

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5
Q

What is the shape of staphylococci?

A

bunches of cocci e.g staph aureus

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6
Q

What do the most widely used antibiotics interfere with?

A

cell wall synthesis e.g b-lactams and glycopeptides

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7
Q

What are the 4 different mechanisms by which antibiotics can develop resistance?

A
  1. Drug inactivation or modification
    - drug produces an enzyme that destroys the antibiotic
  2. alteration of target - or binding site
    - target of antibiotic can change shape so the antibiotic can no longer bind
  3. alteration of metabolic pathway
  4. reduced drug accumulation
    - drugs are pumped out of cell and back into environment
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8
Q

What is amoxicillin and what is it commonly used for?

A
  • very commonly used B-lactam (inhibits cell wall synthesis of bacteria)
  • used for ENT, respiratory and urinary infections
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9
Q

What is B-lactamase?

A

resistant enzyme that breaks down B-lactams

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10
Q

What is co-amoxiclav?

A
  • amoxicillin+ clavulanic acid

- useful against beta-lactamase as clavulanic acid inhibits B-lactamase so it cannot break down

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11
Q

How does flucloxacillin work and what is it used for?

A
  • inhibits cell wall synthesis
  • B-lactam
  • only active against gram +ve
  • mainly used to treat staph aureus infections
  • binds to penicillin binding proteins
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12
Q

Why can Beta lactams not be used to treat MRSA?

A

MRSA = methicillin resistant S.aureus

  • has a mutation in PBPs - resistant to flucoxacillin
  • have to use other antibiotic class e.g vancomycin
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13
Q

What are the 3 types of B-lactams in order from the broadest spectrum to narrowest spectrum?

A
  1. carbapenems (broad spectrum)
  2. cephalosporins
  3. penicillin (narrower spectrum)
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14
Q

What does purulent mean?

A

pus containing

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15
Q

what is the treatment for a high risk patient with community acquired pneumonia?

A

co-amoxiclav and clarithromycin

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16
Q

what is the treatment for a low risk patient with CAP?

A

Amoxicillin

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17
Q

What is the most common cause of community acquired pneumonia?

A

streptococcus pneumoniae

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18
Q

What are the common causes of hospital acquired pneumonia?

A

klebsiella pneumoniae and other gram -ve

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19
Q

What is a common complication of broad spectrum antibiotic use?

A

C.difficile

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20
Q

How do you treat C.difficule?

A

stop current antibiotics and start oral vancomycin - very targeted for C.difficile as it is absorbed by the gut

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21
Q

What are the symptoms of lower urinary tract infection?

A
  • dysuria

- frequency (increased urination)

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22
Q

What are the symptoms of upper UTI?

A
  • fever
  • loin pain
  • tachycardia
  • low BP
23
Q

Where is the infection in a lower UTI?

A

Infection of urethra and bladder

24
Q

Where is the infection in a upper UTI?

A

infection that reaches kidney

is more severe and can cause sepsis - requires broad spectrum until we know cause

25
Q

What is the treatment for meningitis?

A

IV broad spectrum antibiotic: IV ceftriaxone

26
Q

What bacteria causes meningitis in children/ young adults?

A

neisseria meningitides

27
Q

What bacteria causes meningitis in elderly patients?

A

streptococcus pneumoniae

28
Q

What would be the diagnosis if a patient with meningitis also had a non-blanching rash and was systemically unwell with low BP and tachycardia?

A

meningococcal septicaemia - bloodstream infection

29
Q

What is sepsis?

A

life-threatening organ dysfunction caused by a dysregulated host response to infection - a body’s response to an infection injures its own tissues and organs

30
Q

What is the acronym for management of sepsis?

A 
BUFALO:
B-blood cultures
U-urine output 
F-fluids
A-antibiotics
L-lactate 
O-oxygen
31
Q

If a patient presents with a tense, red and swollen leg, what would you suspect?

A
  • cellulitis IF there is a history of trauma

- if not, DVT

32
Q

what is cellulitis caused by?

A

gram positive cocci - staph aureus and strep pyogenes

33
Q

What do we treat cellulitis with?

A

treated with flucloxacillin

34
Q

What is necrotising fasciitis and how do we treat?

A
  • a severe SSTI caused by a polymicrobial mix, but usually involving streptococcus pyogenes
  • treatment: first debridement, then meropenem + clindamycin
35
Q

What is infective endocarditis?

A
  • infection of heart valves

- most common bacteria are S.aureus and streptococci

36
Q

Which are the most well tolerated antibiotics in pregnancy?

A

Beta lactams - penicillins and cephalosporins

37
Q

Which antibiotics should be avoided in pregnancy?

A
  • quinolones - damage to cartilage
  • trimethoprim - folic acid antagonist
  • tetracyclins - deposits and stains bones/teeth
38
Q

What patient factors might influence antibiotic prescriptions?

A
  • allergies
  • elderly can’t take some drugs
  • some patients can’t take oral or IV antibiotics
  • some patients have renal impairment so we have to avoid nephrotoxic drugs
  • pathogen might be resistant
  • some antibiotics interact with drugs a patient is alreayd on
39
Q

What are the symptoms and signs of community acquired pneumonia?

A
  • cough
  • sputum production
  • pleuritic chest pain
  • sore throat
  • runny nose
  • hypoxia
  • tachypneoea
  • abnormal chest examination
  • lower lobe consolidation on X-ray
40
Q

What is tachypnoea?

A

abnormally fast breathing

41
Q

Which tests would you perform on a patient with suspected CAP?

A
  • blood cultures
  • sputum culture
  • chest X-ray
  • lumbar puncture
  • CT/ MRI
  • HIV blood test
42
Q

What is diagnostic iteration?

A

a procedure in which repetition of a sequence of operations (tests) yields results successfully closer to a desired result (a high diagnostic probability)

doing something again and again, usually to improve it

43
Q 
CURB Guidelines:
If a patient has....
1. Low severity CAP
2. Low severity CAP but penicillin allergy 
3. Medium severity CAP
4. Medium severity CAP but penicillin allergy
5. High severity CAP
6. High severity CAP
A
  1. Amoxicillin
  2. Doxycycline or clarithromycin
  3. Amoxicillin + clarithromycin
  4. doxycycline or levofloxacin
  5. Co-amoxiclav IV + Clarithromycin
  6. Levofloxacin
44
Q

What is ESBL?

A
  • Extended spectrum B-lactamase

- antibiotic resistant enzyme in gram -ve bacteria like E.coli

45
Q

Give 6 antibiotics used to provide cover for gram +ve pathogens

A
  • teicoplanin
  • vancomycin
  • flucloxacillin
  • linezoid
  • macrolides e.g clarithromycin
  • penicillin/amoxicillin
46
Q

Give 3 antibiotics used to provide cover for gram -ve pathogens

A
  • aztreonam
  • ciprofloxacin
  • gentamicin
47
Q

Give an example of antibiotic used to treat E.coli cystitis

A
  • nitrofurantoin
  • trimethoprim
  • cephalexin
48
Q

What should be considered before a test is performed?

A
  • whether it is indicated or not indicated e.g a urine culture test is not indicated in a patient with suspected cellulitis
  • how easy they are to do
  • how quick they are to do
  • how expensive
  • how practical
49
Q

What are the 4 steps in selecting an antibiotic?

A
  1. determine what is the infection diagnosis (or working/differential diagnosis)
  2. identify which bacteria cause this infection
  3. identify which antibiotics are effective against these bacteria
  4. of the antibiotics in 3, which have the right charachteristics e.g can be give orally etc
50
Q

What does PO stand for?

A

oral formulation available (drugs can be given orally)

51
Q

If a patient has an intravascular catheter-associated blood stream infection (CRBSI), what test would you perform to confirm the diagnosis?

A

paired through-catheter and peripheral blood cultures (blood culture from catheter)

52
Q

What is the treatmenT for CAP?

A

Amoxicillin/clavulanate and clarithromycin

53
Q

If the bacteria causing an infection is coagulase negative staphylococci infection, what antibiotic would you prescribe?

A

vancomycin- very broad gram +ve antibiotic

Clinical Pathology (57 decks)

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