5: Microbiology Flashcards
What is osteomyelitis?
Inflammation of bone and medulla, usually found in the long bones
Can osteomyelitis recur after treatment?
Yes, so long treatment duration required (e.g 6 weeks)
By which means can osteomyelitis spread?
Contiguously - i.e direct contact
Haematologically - via blood vessels
Osteomyelitis can be diagnosed ___ or ___.
directly (you found the bug)
indirectly (X-RAY/MRI evidence + clinical suspicion)
How is osteomyelitis treated?
Debridement (removal of damaged tissue and foreign material, draining of pus)
Antimicrobial drugs for at least 6 weeks
What are the principles of diagnosis of MSK infections?
Suspect disease - take a history, examine patient
Sample - bone biopsy is gold standard, cross-sectional imaging
Treat - wait for microbiology or treat immediately if septic
Take - blood, lactate, urine analysis
Give - oxygen, fluids, antibiotics
osteomyelitis highly likely in diabetic feet if:
- you can probe all the way to bone
- ulcer >2cm in diameter has been present for >2 months
Why are bone biopsies preferred versus swabs for diagnosing bone infections?
Swabs don’t reach inner medulla
revise characteristic symptoms of inflammation
Bone is highly ___ to infection.
resistant
If in doubt, which organism is responsible for osteomyelitis?
Staph. aureus
When can antibiotics be given to a patient with osteomyelitis?
Once you’ve proved they have an infection i.e a positive biopsy/swab
Or they clearly have sepsis
Coagulase negative Staph. (such as ___ ___) are commensal bacteria but like to colonise foreign material like plastic and metal to cause disease.
Staph. epidermidis
Staphylococci are (aerobic / anaerobic).
aerobic
Which antibiotic is used to treat Staph. aureus?
IV Flucloxacillin
IV Clindamycin (penicillin allergic)
IV Vancomycin (MRSA)
What are three toxins produced by Staph. aureus?
Enterotoxin - food poisoning
SSSST - staph. scalded skin syndrome toxin
PVT - panton valentine leukocidin
Staph. aureus is coagulase ___ and shows up ___ on agar plates.
positive
golden
Which type of fracture tends to get infected?
Open fractures
How are open fractures treated?
Debridement
Reduced & fixation - bone ends brought together
Soft tissue cover
How may you tell that an open fracture is infected?
Wound is healing poorly, doesn’t close up
What is an infectious complication of diabetes, occuring due to venous insufficiency?
Diabetic foot infection
Which sign should raise suspicion of osteomyelitis secondary to diabetic vascular insufficiency?
You can PROBE TO BONE
Is osteomyelitis secondary to diabetic foot ulcers caused by one organism?
Rarely
but treat with fluclox and see what the response is, then add gentamicin (for ?gram negatives) and metronidazole (for anaerobes)
look at antibiotic spectrum of action
If it’s so powerful, why isn’t vancomycin given for MSSA?
Evidence shows that more people with MSSA die on vancomycin compared to flucloxicillin
Flucloxicillin is given intravenously to treat osteomyelitis. When it’s time to switch to an oral drug, what do you use?
Doxycycline
What drugs are used to treat suspected gram negative and anaerobic osteomyelitis (i.e if it’s smelly and rotten?
Gentamicin IV (Gram negatives)
Metronidazole (anaerobes)
What is haematogenous osteomyelitis?
Blood spread of infection to bone
Who tends to get haematogenous osteomyelitis?
Prepubescent children
PWID
Patients with central lines / dialysis / elderly
Outside of the UK, what organism can cause haematogenous osteomyelitis which is very very pus-y?
Mycobacterium tuberculosis
Which organism is the most likely cause of haematogenous osteomyelitis?
Staph. aureus
Which antibiotic covers beta-haemolytic Strep. which may rarely be responsible for osteomyelitis?
Flucloxicillin
so we bueno
What are some unusual sites for osteomyelitis in PWID?
Sternoclavicular joint
Pubic symphysis
i.e if it’s a strange site ask about this
Which test is used to classify Strep. species?
Haemolysis
Which group of Strep. is most commonly seen in osteomyelitis?
What do they look like on haemolysis?
Group A Strep.
Beta (complete) haemolysis - appears white on plate
Patients on which kidney treatment may develop haematogenous osteomyelitis?
Dialysis
osteitis pubis
and clavic osteomyelitis
What are three groups of patients who have an unusual predisposition to osteomyelitis?
Sickle cell anaemics
Gaucher’s disease
SAPHO/CRMO
What is the abnormal casual organism for osteomyelitis in people with sickle cell anaemia?
Salmonella
(or Staph. aureus)
What is a rare genetic disorder associated with an increased risk of bone infections?
Gaucher’s disease
sapho/crmo
What name is given to osteomyelitis affecting the spine?
Vertebral osteomyelitis
Vertebral osteomyelitis tends to cause symptoms associated with the ___ level it’s at.
spinal
How does vertebral osteomyelitis tend to spread?
Haematogenous
What organisms can cause vertebral osteomyelitis?
Staph. aureus
Gram negatives
Anaerobes
Mycoplasma tuberculosis
What are some symptoms of vertebral osteomyelitis?
Fever
Insidious pain
Raised CRPs
Occasionally raised white cell count
How is suspected vertebral osteomyelitis investigated?
BIOPSY (direct)
MRI/CT scan (indirect)
How is vertebral osteomyelitis treated?
Drainage of epidural / psoas abscesses
Antibiotics for 6 weeks
When should an MRI be repeated in patients with vertebral osteomyelitis?
Unexplained increases in inflammatory markers
Increasing pain
New signs/symptoms
What is the drug of choice for vertebral osteomyelitis in Scotland?
Flucloxacillin
Internationally, what organism may cause vertebral osteomyelitis?
What is the disease called in this cause?
TB
Pott’s disease
What must be offered to patients presenting with skeletal TB?
HIV test
Is skeletal TB limited to one vertebral disc?
No, crosses discs causing a shitload of damage
