Which pathogens most commonly cause osteomyelitis in... - Newborns and children - Adults

- Newborns and children: Staph aureus, Group B strep - Adults: Staph aureus (frequency of gram -ve bacteria increased in the elderly)

Microbiology Flashcards by Leah Redford

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

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

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How can staph aureus be distinguished from other staph spp?

It is the only coagulase +ve staph spp.

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

It is the only novobiocin resistant staph spp

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Which antibiotic is first-line for…

Staph aureus
MRSA

Staph aureus: Flucloxacillin (or Doxycycline if allergic)

MRSA: Vancomycin

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

Rifampicin

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

Abscesses and necrotic lesions

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What is osteomyelitis?

Inflammation of bone and the medullary cavity

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

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

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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Which pathogens most commonly cause osteomyelitis in…

Newborns and children
Adults

Newborns and children: Staph aureus, Group B strep

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

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What symptoms should cause clinical suspicion of infection?

Fever
Pain
Inflammation
Loss of function

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Describe the clinical presentation of acute vs chronic osteomyelitis

Acute: abrupt onset of intense pain, erythema

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

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Which blood investigation may be useful in osteomyelitis?

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

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What is a probe to bone (PTB) test?

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

Bone biopsy

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List indirect methods for confirming diagnosis of infection (2)

X-ray (may be normal)

Histology (inflammation)

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List direct methods for confirming diagnosis of infection (2)

Microbial growth from sample

PCR

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Name 4 different types of osteomyelitis

Open fracture
Diabetic/venous insufficiency
Haematogenous
Vertebral

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Haematogenous osteomyelitis is most common in… (5)

Pre-pubescent children
PWID
Central lines/dialysis patients
Elderly
Sickle cell disease

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The most common causative organism for haematogenous osteomyelitis is…

Staph aureus

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What are the 2 steps for treatment of osteomyelitis?

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

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

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

Gram +ve

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

Gram -ve

IV: Gentamicin
Oral: Cotrimoxazole/ Doxycycline

Anaerobes
- Metronidazole

What is the usual duration of antibiotic treatment for osteomyelitis?

6 weeks

Define... - Primary bacteraemia - Complicated bacteraemia

- Primary bacteraemia: bacteraemia with no known cause | - Complicated bacteraemia: bacteraemia with systemic effects e.g., infective endocarditis

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

Group A strep | Group B strep

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

Strep pneumoniae - pathogen that most often causes pneumonia Strep viridans - commensal of mouth, throat, vagina etc

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

Enterococcus spp - commensals of bowel, more commonly cause UTI

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

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

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

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

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

- Direct inoculation at time of surgery | - Seeding of joint at a later time due to haematogenous spread

``` What are the most common organisms that cause... - Early prosthetic joint infections - Chronic prosthetic joint infections - Haematogenous joint infections ...? ```

- 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

What is the difference between planktonic and sessile bacteria?

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

What is a biofilm?

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

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

Culture (at least 5 tissue samples to find causative organism) Blood culture CRP Radiography

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

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

What is septic arthritis? How is it introduced?

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

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

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

List diagnostic investigations for septic arthritis (3)

Blood culture (take in all cases as haematogenous spread is most common cause) Joint fluid aspiration for microscopy, culture and sensitivity Imaging (xray, MRI)

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

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

What is the empirical treatment for septic arthritis? | What about for <5 y/o?

High dose IV flucloxacillin Add Ceftriaxone (for H influenza cover)

What is the directed treatment plan for septic arthritis?

- 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

Describe the histological appearance of clostridium tetani

Gram +ve strictly anaerobic rods

Which organism causes tetanus?

Clostridium tetani

Name the first-line antibiotic used to treat infection with each of the following organisms: - Staph aureus - Staph epidermis - Strep pyogenes - Gram -ves - Anaerobes

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

What is tetanus?

A toxin mediated illness that results in spastic paralysis

How does clostridium tetani cause tetanus?

It releases a neurotoxin which binds to inhibitory neurones and prevents release of neurotransmitters This causes spastic paralysis

How is tetanus diagnosed?

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

What is the treatment for tetanus?

- Surgical debridement - Antitoxin - Supportive measures - Antibiotics (penicillin and metronidazole) - Booster vaccination

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

Survivors are not immune to future infection

List some possible causes of myositis? (4)

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

How does clostridium tetani enter a host?

Spores (often found in soil) enter through a wound

What is Gaucher's disease?

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

What is SAPHO?

A rare inflammatory disorder affecting the bone, joints and skin, causing pain and swelling in those areas (synovitis acne pustolosis hyperostosis osteitis)

What is CRMO?

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