Microbiology Flashcards
What are some less common pathogens that can cause BJI or PJI?
Pseudomonas aeruginosa, Kingella in children
What are some risk factors of BJI?
Implants, immunosuppressed, diabetes, IVDU
What is the clinical presentation of acute BJI?
Temperature/systemic signs, pain/swelling/redness, reduced mobility/joint movement/held in flexed position.
What is the clinical presentation of acute BJI in children, other than the usual symptoms?
Listless, not feeding/playing, cranky
Two or more or which symptoms are needed for a diagnosis of Systemic Inflammatory Response Syndrome (SIRS)
Temp >38 or 90bpm, resp rate >20 or PaCO2 12000 cells/mm3 or
What is septic arthritis?
Infection of joint space
How are organisms introduced in septic arthritis?
Haematogenous spread, contiguous spread (via infected bone), direct inoculation (injection or trauma)
What organisms commonly cause septic arthritis?
Mainly MSSA, streptococci. Rarely haemophilus influenza, Neisseria gonorrhoea
What tests are used to diagnose acute septic arthritis?
Blood culture if pyrexial (+ve in 30-60%), CRP, FBC, U&E, lactate, ESR etc. Joint fluid aspirate/washout for microscopy& culture, crystals (gout, pseudogout) white cells &gram stain, USS, XR, MRI,CT, Bone scan
What is the antibiotic treatment in acute septic arthritis?
Empiric treatment for staph aureus-flucox high dose.
What is osteomyelitis?
Inflammation of bone and medullary cavity, usually long bones or vertabrae
What are the common pathogens in acute and chronic osteomyelitis?
Acute-MSSA or streptococci, Chronic- Myco tuberculosis, Pseudomonas aeruginosa, salmonella, brucella, coliforms
How are organisms introduced in osteomyelitis?
Spread- haematogenous, contiguous, PVD associated, prosthesis associated
What is the most likely method of spread, and locations of acute osteomyelitis?
Haematogenous-especially femur/tibia. Metaphysis is intracapsular so may extend into joint space (shoulder, ankle, hip, elbow).
What are infants more at risk of if they have acute osteomyelitis?
Septic arthritis due to vessels crossing metaphysis to epiphysis
How does chronic osteomyelitis occur?
Delay in treating acute infection leads to higher risk of abscess, permanent damage, septicaemia etc.
Describe SIRS in chronic osteomyelitis?
Usually absent- no immediate need for antibiotic treatment
How is osteomyelitis diagnosed?
Blood culture if pyrexial, bone biopsy/washout if possible for microscopy/culture.
How is osteomyelitis managed?
Empiric high dose fluclox. Modify after C&S. 4-8 wks.
What are some risk factors for infection in prosthetic joints?
Rheumatoid arthritis, diabetes, malnutrition, obesity
Describe the timeframe, route, signs and cause of early postop implant infection
0-3 months. Perioperative. Fever, effusion, warmth drainage. Staph aureus, strep, enterococci
Describe the timeframe, route, signs and cause of early delayed (low grade) implant infection
3-24/12. Perioperative. Persistent pain, device loosening, fistula. Coag -ve staph, P. acnes.
Describe the timeframe, route, signs and cause of early late implant infection
> 24/12. Haematogenous. Acute or subsacute. S. aureus, E. coli
When are CoNs likely to cause an infection?
If prosthetic material present, or presence of biofilm
How do you diagnosis PJI?
Cause is often common contaminants. Culture-tissue&bone. Blood culture (rarely +ve), CRP, WCC etc, radiology
How are PJI’s treated?
Ideally prosthesis removal and cement. 6 wks. Re-implantation after antibiotic treatment.
What is necrotizing fasciitis?
Acute & severe infection of subcutaneous soft tissues that can effect limbs, abdo wall, perineal & groin area, post op wound. Can cross tissue plains
What is the clinical presentation of necrotizing fasciitis?
Highly painful, some inflammation. Rapid tissue spread. Systemic toxicity
What pathogens cause type 1 necrotizing fasciitis?
Anaerobes plus multiple other bacteria-synergistic gangrene
What pathogens cause type 2 necrotizing fasciitis (flesh eating bacteria)
Group A strep, alone or in combination with S.aureus
How is necrotizing fasciitis diagnosed?
Pain disproportionate to superficial appearances. Swabs & tissue biopsy for microbiology gram stain/culture. Blood cultures. CRP, FBC, clotting, U&E etc
What is the treatment for necrotizing fasciitis?
Surgical debridement.
Strep pyogenes- penicillin + clindamycin. Pen kills actively multiplying bacteria in exponential growth phase, clindamycin stops bacterial protein production-switches off toxin. Syngergistic: pip-taz, clindamycin, gentamicin
What pathogen commonly causes gas gangrene?
Clostridium perfringens (gram +ve strictly anaerobic rods)- spores
What is the aetiology of gas gangrene?
Spores into tissue. Predisposing factors- dead tissue and anaerobic conditions. Spores germinate-leads to accumulation of bubbles in tissues-space gas gangrene ‘crepitus’
What is the treatment of gangrene?
Urgent debridement. Antibiotics in high doses-penicillin, metronidazole (either/both). +/- hyperbaric oxygen
What pathogen commonly causes tetanus?
Clostridium tetani-gram +ve strictly anaerobic rods. Spores are found in soil, gardens, animal bites etc
What is the clinical presentation of tetanus?
Spastic paralysis as neurotoxin. Lock jaw-muscles spasm. Incubation period - 4 days to several wks
How does spastic paralysis occur in tetanus?
Neurotoxin released by pathogen binds to inhibitory neurones, preventing release of neurotransmitters
What is the antibiotic choice for staph/strep infections?
Flucloxacillin: vancomycin, also for diptheroids, CoNS, MRSA. Clindamycin if pen allergic. Used for antitoxin properties (PVL, Group A strep), tissue penetration
What is the antibiotic choice for coliforms?
Gentamicin, sometimes cephalosporin-ceftriazxone, sometimes ciprofloxaxin (oral)
What is biofilm?
Slow growing: bacteria coated in ‘slime’ (protein plus polysaccharide)
What does biofilm do?
Protects bacteria from immune system and antibiotics
What is common of bacteria in abscesses or biofilms?
Phenotypically resistant to antibiotics
What is the Tayside protocol for PJI?
No antibiotic pre-operatively
Minimum three bone/ tissue/ pus samples for culture
Minimum 6 weeks antibiotics before clean surgery
What is the antibiotic of choice for gram +ve PJI, and if pen allergic or methicillin resistant?
Flucloxacillin, vancomycin and teicoplanin
What is the antibiotic choice for gram -ve PJI?
Cotrimoxazole, amoxicillin, ciprofloxacin, ceftriaxone
How do you assess response of treatment in PJI?
Continue treatment for 2 weeks after resolution of infection clinical signs. Repeat MRI/CT. Bone scans unhelpful till 1y after surgery. Can’t be sure of cure till 2y post treatment
What prophylaxis is needed in orthopaedics?
Essential for prosthetic joint/implant-co amoxiclax 1.2g peri op & 2 post op doses. Screen for MRSA post op-decolonize if +ve. If pen allergy-co-trimoxazole. Start 24h
What is an involucrum?
Bone forming on the outside of existing bone
What are the first line antibiotics for cellulitis?
Flucloxacillin and benzylpenicillin
