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LR Musculoskeletal > Microbiology > Flashcards

Microbiology Flashcards

1
Q

What does it mean that staphylococcus sp. are aerobic and facultatively anaerobic?

A

They grow best aerobically (in air) but also grow anaerobically

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2
Q

How can staph aureus be distinguished from other staph spp?

A

It is the only coagulase +ve staph spp.

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3
Q

How can coagulase -ve staph saprophyticus be distinguished from other staph spp?

A

It is the only novobiocin resistant staph spp

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4
Q

Which antibiotic is first-line for…

  • Staph aureus
  • MRSA
A

Staph aureus: Flucloxacillin (or Doxycycline if allergic)

MRSA: Vancomycin

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5
Q

Which antibiotic may be used alongside another to treat staph aureus but never by itself?

A

Rifampicin

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6
Q

PVL toxin secreted by staph aureus/MRSA can cause formation of…

A

Abscesses and necrotic lesions

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7
Q

What is osteomyelitis?

A

Inflammation of bone and the medullary cavity

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8
Q

Describe haematogenous osteomyelitis and which bones are most often affected in children vs adults

A
  • Caused by blood spread
  • Usually monomicrobial (one organism)
  • Most common in long bones in children
  • Most common in vertebrae in adults (due to good vascular supply)
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9
Q

Describe contiguous osteomyelitis and the most common causes in the young vs elderly

A
  • Caused by local infection
  • Usually polymicrobial (more than one bacteria)
  • Seen after injury or surgery in the young
  • Seen due to pressure sores or vascular insufficiency in the elderly
  • Seen in diabetic foot
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10
Q

Which pathogens most commonly cause osteomyelitis in…

  • Newborns and children
  • Adults
A
  • Newborns and children: Staph aureus, Group B strep

- Adults: Staph aureus (frequency of gram -ve bacteria increased in the elderly)

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11
Q

What symptoms should cause clinical suspicion of infection?

A
  • Fever
  • Pain
  • Inflammation
  • Loss of function
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12
Q

Describe the clinical presentation of acute vs chronic osteomyelitis

A

Acute: abrupt onset of intense pain, erythema

Chronic: gradually worsening pain over months/years, loss of function

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13
Q

Which blood investigation may be useful in osteomyelitis?

A

CRP is useful for monitoring response to treatment (raised in infection)

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14
Q

What is a probe to bone (PTB) test?

A

A test used in the examination of potential osteomyelitis

A probe is inserted into a suspicious ulcer and if a solid ‘click’ is heard and a gritty surface is felt inside, that means bone has been hit

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15
Q

What is the gold standard method for taking a sample for osteomyelitis investigations?

A

Bone biopsy

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16
Q

List indirect methods for confirming diagnosis of infection (2)

A

X-ray (may be normal)

Histology (inflammation)

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17
Q

List direct methods for confirming diagnosis of infection (2)

A

Microbial growth from sample

PCR

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18
Q

Name 4 different types of osteomyelitis

A
  1. Open fracture
  2. Diabetic/venous insufficiency
  3. Haematogenous
  4. Vertebral
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19
Q

Haematogenous osteomyelitis is most common in… (5)

A
  • Pre-pubescent children
  • PWID
  • Central lines/dialysis patients
  • Elderly
  • Sickle cell disease
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20
Q

The most common causative organism for haematogenous osteomyelitis is…

A

Staph aureus

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21
Q

What are the 2 steps for treatment of osteomyelitis?

A
  • Source control (may require surgical debridement in some cases)
  • Antibiotics (can fight infection now that source is controlled)
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22
Q

Patients should be given empirical treatment while awaiting a microbiological diagnosis. T/F?

A

False

If the patient is not acutely unwell, wait for microbiology then use specific antibiotic

Empirical treatment is only used if the patient is septic or has a soft tissue infection

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23
Q 
Name the first-line IV and oral antibiotics used for treating...
- Gram +ve 
- Gram -ve
- Anaerobes
... bone infection
A

Gram +ve

  • IV: Flucloxacillin (Vancomycin if penicillin allergic)
  • Oral: Doxycycline

Gram -ve

  • IV: Gentamicin
  • Oral: Cotrimoxazole/ Doxycycline

Anaerobes
- Metronidazole

24
Q

What is the usual duration of antibiotic treatment for osteomyelitis?

A

6 weeks

25
Q

Define…

  • Primary bacteraemia
  • Complicated bacteraemia
A
  • Primary bacteraemia: bacteraemia with no known cause

- Complicated bacteraemia: bacteraemia with systemic effects e.g., infective endocarditis

26
Q

Which beta-haemolytic strep are most often seen in osteomyelitis?

A

Group A strep

Group B strep

27
Q

Which alpha-haemolytic strep are most often seen in osteomyelitis and where are the more often found?

A

Strep pneumoniae - pathogen that most often causes pneumonia

Strep viridans - commensal of mouth, throat, vagina etc

28
Q

Which non-haemolytic strep are most often seen in osteomyelitis and where are they more commonly found?

A

Enterococcus spp - commensals of bowel, more commonly cause UTI

29
Q

Why are people with sickle cell disease at higher risk of osteomyelitis?

A

They are prone to bone infarcts which are high risk for infection (staph aureus most common)

30
Q

What is the most common presentation of skeletal tuberculosis (Pott’s disease)?

A

Chronic back pain localised to the site of involvement over months or years

31
Q

What are the 2 mechanisms by which a prosthetic joint can become infected?

A
  • Direct inoculation at time of surgery

- Seeding of joint at a later time due to haematogenous spread

32
Q 
What are the most common organisms that cause...
- Early prosthetic joint infections
- Chronic prosthetic joint infections
- Haematogenous joint infections
...?
A
  • Early: Staph aureus, coagulase -ve staph
  • Chronic: (lower virulence organisms) coagulase -ve staph, cutibacterium, corynebacterium, staph aureus
  • Haematogenous: (high virulence, abrupt onset) staph aureus, gram -ve bacteria
33
Q

What is the difference between planktonic and sessile bacteria?

A

Planktonic: active and replicate rapidly, cause most inflammatory symptoms and are susceptible to antibiotics

Sessile: dormant bacteria that form biofilms and are more resistant to antibiotics

34
Q

What is a biofilm?

A

A community of sessile microbes that adhere to a surface (e.g., a prosthetic or body surface) and show greater resistance to antibiotics

35
Q

Which tests should be carried out to diagnose prosthetic joint infection?

A

Culture (at least 5 tissue samples to find causative organism)

Blood culture
CRP
Radiography

36
Q

Which antibiotics are given empirically to treat prosthetic joint infections while awaiting culture results?

A

Vancomycin (gram +ve cover) and Gentamicin (gram -ve bacilli cover)

37
Q

What is septic arthritis? How is it introduced?

A

Infection of the joint space

By haematogenous spread (most common), direct invasion of penetrating wound or spread from infectious bone/soft tissue

38
Q

What are the most common organisms to cause of septic arthritis? (4)

A

Staph aureus
Streptococci
N gonorrhoea (think STIs)
H influenza (think preschool children)

39
Q

List diagnostic investigations for septic arthritis (3)

A

Blood culture (take in all cases as haematogenous spread is most common cause)

Joint fluid aspiration for microscopy, culture and sensitivity

Imaging (xray, MRI)

40
Q

Describe the colour, WCC and PMN count of fluid aspirate in septic arthritis

A

Colour: opaque
WCC >100,000
PMN count >90%

41
Q

What is the empirical treatment for septic arthritis?

What about for <5 y/o?

A

High dose IV flucloxacillin

Add Ceftriaxone (for H influenza cover)

42
Q

What is the directed treatment plan for septic arthritis?

A
  • At least 1 week IV antibiotics then switch to oral
  • Washout to reduce bacterial load and debris
  • Treatment usually 2-4 weeks but can progress to 6 weeks if required
43
Q

Describe the histological appearance of clostridium tetani

A

Gram +ve strictly anaerobic rods

44
Q

Which organism causes tetanus?

A

Clostridium tetani

45
Q

Name the first-line antibiotic used to treat infection with each of the following organisms:

  • Staph aureus
  • Staph epidermis
  • Strep pyogenes
  • Gram -ves
  • Anaerobes
A
  • Staph aureus: Flucloxacillin
  • Staph epidermis: Vancomycin
  • Strep pyogenes: Doxycycline
  • Gram -ves: Clindamycin
  • Anaerobes: Metronidazole
    Cotrimoxazol
46
Q

What is tetanus?

A

A toxin mediated illness that results in spastic paralysis

47
Q

How does clostridium tetani cause tetanus?

A

It releases a neurotoxin which binds to inhibitory neurones and prevents release of neurotransmitters

This causes spastic paralysis

48
Q

How is tetanus diagnosed?

A
  • Clinical spastic paralysis
  • Culture (difficult to obtain, anaerobic gram +ve, drumstick shaped spore)
  • Serum and urine toxin assays
49
Q

What is the treatment for tetanus?

A
  • Surgical debridement
  • Antitoxin
  • Supportive measures
  • Antibiotics (penicillin and metronidazole)
  • Booster vaccination
50
Q

Why do people recovering from tetanus still need a booster tetanus injection?

A

Survivors are not immune to future infection

51
Q

List some possible causes of myositis? (4)

A
  • Viral (e.g., HIV, HTLV-1, influenza, CMV)
  • Bacterial (e.g., staph aureus, strep viridans)
  • Fungal
  • Parasites
52
Q

How does clostridium tetani enter a host?

A

Spores (often found in soil) enter through a wound

53
Q

What is Gaucher’s disease?

A

A genetic lysosomal storage disorder that causes lipids to build up in organs such as the liver and spleen

54
Q

What is SAPHO?

A

A rare inflammatory disorder affecting the bone, joints and skin, causing pain and swelling in those areas

(synovitis acne pustolosis hyperostosis osteitis)

55
Q

What is CRMO?

A

A rare autoimmune disease that causes inflammation of the bones, most often in children

LR Musculoskeletal (6 decks)

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