Flashcards in Microbiology Deck (59)
What organisms are typically involved in a prosthetic joint infection?
Coagulase negative Staph
What organisms typically cause septic arthritis?
What organisms tend to be responsible for post-traumativ infections?
What bacteria are often involved in vertebral osteomyelitis?
What organisms typically cause diabetic foot infections?
What bacteria is a less common infective organism but is more common in kids under 5 years old?
A 3 year old child presents with pain in his right hip. his mother says he hasn't been feeding very well. On examination his temperature is 39.1, and there is obvious swelling and erythema over his right hip. Any attempt to touch or move the hip is met with obvious pain.
Acute bone and joint infection
How do we classify Systemic Inflammatory Response Syndrome (SIRS)?
Two or more of:
- Temperature >38 or 20 or PaCO2 12,000 cells/mm^3 OR 90
What are some rarer causes of septic arthritis?
When would a blood culture be carried out?
If the patient is pyrexial
What is the empiric treatment for septic arthritis in:
1. High dose flucloxacillin
2. High dose flucloxacillin and ceftriaxone
How long does septic arthritis treatment continue?
What is osteomyelitis?
Inflammation of bone and medullary cavity
Where does osteomyelitis tend to occur?
What are acute causes of osteomyelitis?
What bacteria may cause chronic osteomyelitis?
How long does acute osteomyelitis last?
Few days to
How might osteomyelitis spread into the joint space?
Since metaphysis is intracapsular in these joints:
Why are infants at an increased risk of septic arthritis after osteomyelitis?
Vessels cross into epiphysis
What processes occur that may lead to chronic osteomyelitis?
2. Permanent damage
Why is there not an immediate need for antibiotics in chronic osteomyelitis?
SIRS is usually absent
When would we start antibiotics in chronic osteomyelitis?
Once we achieve culture results
What is the empiric treatment for osteomyelitis?
High dose flucloxacillin:
- Modify after culture
- 4 to 8 weeks
Which of the following is not a risk factor for a prosthetic joint infection:
What are the three types of implant infection?
Early postoperative (0-3 months)
Delayed (Low grade) (3-24 months)
Late (> 24 months)
A patient presents with persistent pain in her left hip. She had a hip replacement 18 months ago. She is a diabetic and has a BMI of 32.
What features of CoNS make them difficult to treat?
Produce a biofilm over prosthesis
What cultures may aid in the diagnosis of a PJI?
Tissue and bone (multiple)
How do we treat a PJI?
Remove prosthesis and cement
Treat with antibiotics
Wait > 6 weeks until joint is re-implanted
How do we treat necrotising fasciitis?
Empirical antibiotics (Strep pyogenes):
- Penicillin - Kills bacterial
- Clindamycin - Reduces toxin production
What bacteria causes gas gangrene?
- Gram positive bacilli
- Strictly anaerobic
What is the pathogenesis of gas gangrene?
1. Spores in bowel/environment
2. Spores move into tissue
3. Spores germinate
4. Gas bubble accumulation
What factors predispose to gas gangrene?
How is gas gangrene treated
1. Urgent surgical debridement
2. High dose antibiotics
- +/- Metronidazole
3. +/- Hyperbaric oxygen
What causes tetanus?
- Gram positive bacilli
- Strictly anaerobic
Where are the spores that cause tetanus found?
What happens in tetanus?
1. Neurotoxin produced
2. Neurotoxin binds to inhibitory neurones
3. Neurotransmitter release prevented
4. Spastic paralysis
Are the bacteria that cause tetanus invasive?
(All toxin driven)
How is tetanus treated?
- 2, 3 and 4 months
What are the choice antibiotics for Staph and Strep?
What other uses exist for vancomycin?
If penicillin allergic
What is clindamycin effective in?
What antibiotic choices treat coliforms?
Sometimes PO ciprofloxacin
What is a biofilm composed of?
What does a biofilm do?
Protects bacteria from:
- Immune system
What environment does a biofilm produce?
Low pH - 5
Free nucelic acids
What is the Tayside Protocol for PJI?
1. No pre-op antibiotics
2. Minimum three bone/tissue/pus culture samples
3. Minimum 6 weeks antibiotics before clean surgery
Why do we take three bone samples for culture?
Superficial swabs useless
Bone samples can be contaminated with skin flora
Some infections caused by skin flora:
- eg. CoNS
What is the Tayside Protocol for PJIs caused by gram positive bacteria?
If penicillin allergic - Vancomycin
If MRSA - Teicoplanin
What is the Tayside Protocol for PJIs caused by gram negative bacteria?
How long do the following antibiotic treatments last:
1. DAIR (Debridement, Antibiotics, Irrigation, Retention of prosthesis)
2. One stage
3. Two stage
4. Hip PJI
5. Knee PJI
1. 4 weeks IV then 8 weeks PO
2. 4 weeks IV then implant then 8 weeks PO
3. 6 weeks IV then 6 weeks nothing then implant
4. Treatment minimum 3 months
5. Treatment minimum 6 months
How can we assess response in PJI?
How long til we can be sure a PJI has been cured?
> 2 years
What are the general principles for surgical prophylaxis (SIGN 104)?
1. 1st dose within 60 minutes of start of procedure
2. Prophylaxis should not last > 24 hours
3. Needs to be in tissue at time of surgery and cover relevant pathogens
When is surgical prophylaxis used in orthopaedics?
Prosthetic joint implant:
> 1.2g peri-operatively
> Plus two post-operative doses
What do we do if MRSA is discovered pre-op?
Restart peri-op antibiotics
What surgical prophylaxis is used if a patient is penicillin allergic?
What type of vaccine is used to prevent tetanus?