Microbiology Flashcards
What is septic arthritis?
Infection of joint space
List 3 ways that pathogens can be introduced into the joint
Haematogenous from distant focus of infection
Contiguous from infected bone
Direct inoculation from trauma/injection
Which 2 organisms usually cause septic arthritis?
Staph aureus
Streptococci
Name 2 rare causes of septic arthritis
H. influenza
N. gonorrhoea
How is septic arthritis diagnosed?
BLOOD CULTURE
Joint aspirate for M C&S
Ultrasound
What is the empirical treatment for septic arthritis?
IV Flucloxacillin
How is a patient
IV Flucloxacillin + Ceftriaxone
What is osteomyelitis?
Inflammation of bone and medullary cavity
Usu long bones/verterbrae
List 2 causes of acute osteomyelitis
Staph aureus
Streptococci
List 5 causes of chronic osteomyelitis
M. tuberculosis P. aeruginosa Salmonella (esp sickle cell pts) Brucella Coliforms
List 4 ways that osteomyelitis can be spread
Haematogenous
Contiguous
Via prostheses
Associated with peripheral vascular disease
State 4 risk factors associated with developing infection in prosthetic joints
Rheumatoid arthritis
Diabetes
Malnutrition
Obesity
State 3 types of implant infections, and their timescales
Early post-op: 0-3 months
Delayed: 3-24 months
Late: >24 months
Where in the body can coagulase -ve staph (CoNS) be found?
Skin - commensals
- low virulence
- produces biofilm
How is a diagnosis of PJI made?
Multiple bacterial cultures
- from tissue and bone
How is PJI treated?
Ideally remove implant and cement
6wks antibiotic treatment before re-implantation
What is necrotising fasciitis?
Acute severe infection of subcutaneous soft tissue
Crosses tissue plains
Rapidly progresses to mortality
How does necrotising fasciitis present?
Exceptionally painful
Skin looks fairly normal
Systemic toxicity
How many types of necrotising fasciitis are there?
2
What is type I necrotising fasciitis?
Anaerobes
+ other bacteria
“synergistic gangrene”
What is type II necrotising fasciitis>
Group A strep
affects young and otherwise well people
How is necrotising fasciitis diagnosed?
Observation - pain disproportionate to physical appearance
Swabs and biopsy for M C & S
How is necrotising fasciitis treated?
Surgical debridement
Strep pyogenes: penicillin + clindamycin
What is gas gangrene?
Rapidly spreading gangrene caused by soil bacteria that emits malodorous gas
Which organism is most associated with gas gangrene?
Clostridium perfringens
- strictly gram +ve anaerobic rods
What is the most important feature of the bacteria that cause gas gangrene?
They produce spores
How does gas gangrene brew?
Spores germinate in otherwise unhealthy cells
Leads to accumulation of gas in tissues - ‘crepitus’
What is the treatment for gas gangrene?
Urgent surgical debridement
IV Penicillin +/- Metronidazole
Oxygen
What is tetanus?
Bacterial infection causing contraction and spasm of voluntary muscles
Which bacterium is responsible for tetanus?
Clostridium tetani
- found in soil, animal bites
How does clostridium tetani cause the condition?
Neurotoxin binds to and prevents release of neurotransmitters
Leads to spastic paralysis - lock jaw
All toxin relateed, non invasive in tissues
How is tetanus treated?
Antitoxin
+ penicillin
+ debridement (esp bite area)
What type of vaccination is given to prevent tetanus infection?
Toxoid vaccine + boosters
Which 3 antibiotics can be used to treat staph and strep PJIs?
Flucloxacillin
Vancomycin - also diphtheriods
Clindamycin - antitoxin properties
List 3 antibiotics that can be used in PJIs caused by coliforms
Gentamicin
Ceftriaxone
Ciprofloxacin
What is a biofilm?
Slime layer surrounding a group of bacteria stuck onto bone/prostheses
Prevents penetration of normal doses of antibiotic treatment
What are the 3 principles of treating a PJI with antibiotics in the presence of biofilms
High dose (usu IV)
Long term
Bacteriocidal
What is the surgical treatment of PJIs
Debridement
- may retain prosthesis
- prosthesis removal may be in 1 or 2 stages
Which organisms normally cause acute primary PJIs?
Staph aureus
Streptococci
Which organisms normally cause chronic PJIs?
CoNS
Propionibacteria
List the 3 protocol features of PJI surgery
No pre-op antibiotics
Min 6weeks antibiotic treatment before surgery
Min 3 bone samples for culture
Which 2 antibiotics are used to treat gram positive PJIs?
Fluclox
Vancomycin (if penicillin resistant)
Which 2 antibiotics are used to treat gram negative PJIs?
Cotrimoxazole
Amoxicillin rare
List 2 standards for prophylactic antibiotic treatment for PJI surgery
1st dose must be given within an hour of knife-to-skin
Prophylaxis should not extend > 24hr of surgery
Name the standard orthopaedic prophylaxis
1.2g coamoxiclav, peri op
+ 2 post-op doses
Which antibiotic is administered as prophylaxis if the patient is penicillin allergic?
Cotrimoxazole
