Microbiology Flashcards
BJI
bone &joint infection
PJI
prosthetic joint infection
MSSA
meticillin sensitive staph aureus
MRSA
meticillin resistant staph aureus
common PJI bacteria
S. Aureus, coagulase negative staph, strep. spp, propionibacterium acnes
common septic arthritis infections
staph aureus, streptococci
common post-traumatic infections
staph aureus, polymicrobial coliforms, pseudomonas
common vertebral osteomyelitis infections
staph aureus, coliforms, strep spp, mycobacterium tuberculosis
common diabetic foot infections
staph aureus, strep spp, coliforms, pseudomonas, anaerobes
less common bacteria species but must be remembered
psuedomonas aeruginosa
kingella in children
risk factors for infections
sickle cell anaemia
immunocompromised patient
diabetes
clinical presentation of acute BJI in adults
Temperature/systemic signs
Pain/swelling/redness over area
Reduced mobility/movement of joint/held in flexed position
clinical presentation of acute BJI in children
listless, not feeding/playing, cranky
the category for systemic inflammatory response syndrome (SIRS)
two or more of:
- Temperature >38C or 90 beats/min
- Respiratory rate >20 breaths/min or PaCO2 12,000 cells/mm3 or
how can organisms be introduced into the joint space in septic arthritis?
Haematogenous spread Contiguous spread (eg infected bone) Direct inoculation (injection or trauma)
what tests should be done to diagnose acute septic arthritis?
Blood culture if pyrexial (positive in 30-60% cases)
CRP, FBC, U&E, lactate, ESR etc
Joint fluid aspirate/washout for microscopy* & culture
crystals (gout, pseudogout) white cells & gram stain
Ultrasound scan, plain X-ray MRI, CT, bone scan
how would you treat septic arthritis in someone over 5 years old?
high dose flucloxacillin for 2-4 weeks
look for source of organisms
adjust with culture results
how would you treat septic arthritis in someone under 5 years old?
high does flucloxacillin + ceftriaxone for 2-4 weeks
look for source of organisms
adjust with culture results
why is ceftriaxone added into the treatment of septic arthritis for children under the age of 5?
to cover H. influenzae & Kingella
what is osteomyelitis?
Inflammation of bone & medullary cavity, usually long bones or vertabrae
what organisms is it likely to be in acute osteomyelitis?
MSSA
streptococci
what organisms could it be in chronic osteomyelitis?
mycobacterium tuberculosis pseudomonas aeruginosa salmonella brucella coliforms
how can osteomyelitis be spread?
Haematogenous
Contiguous
Peripheral vascular disease associated
Prosthesis associated
what is the most likely way of spreading in acute osteomyelitis?
haematogenous especially in femur/tibia
what is the risk of osteomyelitis in shoulder/ankle/hip/elbow?
metaphysis is intracapsular so may extend into joint space
why are infants more at risk of septic arthritis as well as acute osteomyelitis?
due to vessels crossing metaphysis to epiphysis
how does chronic osteomyelitis come about?
Delay in treating acute infection leads to higher risk of abscess, permanent damage, septicaemia etc
why should you always try to delay antibiotic treatment in osteomyelitis?
until specimens have been obtained for culture
how is osteomyelitis diagnosed?
Blood culture if pyrexial
Bone biopsy/washout if possible for microscopy & culture
how is osteomyelitis treated?
high dose flucloxacillin (4-8 weeks)
modify treatment after results of culture
what are the risk factors for PJI?
RA
Diabetes
Malnutrition
Obesity
what are the three types of implant infection?
early postoperative
delayed (low grade)
late
when does early postoperative PJI come on?
0-3 months after operation
what route of spread is used in early postoperative PJI?
perioperatice
what signs are present in early postoperative PJI?
fever
effusion
warmth drainage
what bacteria are likely to be causing early postoperative PJI?
staph aureus
streptococci
enterococci
when does delayed PJI come on?
3-24 months after operation
what is the route of spread in delayed PJI?
perioperative
what signs are present in delayed PJI?
persistent pain
device loosening
fistula
what bacteria is likely to be causing delayed PJI?
coagulase negative staph
P. acnes
when does late PJI come on?
more than 24 months after operation
what is the route of spread in late PJI?
haematogenous
what signs are present in late PJI?
acute or subacute
what bacteria is likely to be causing late PJI?
staph. aureus
E. coli
are coagulase negative staph commensal?
yes, part of normal skin flora
describe the virulence of coagulase negative staph
low virulence
do coagulase negative staph create a biofilm
yes
how is PJI diagnosed?
multiple cultures - tissue & bone
blood culture
CRP, WCC etc.
radiological investigations
why is PJI often difficult to diagnose?
as it’s often caused by organisms that are common contaminants
what is the treatment of PJI?
Ideally removal of prosthesis & cement.
At least 6 weeks with no joint & on antibiotics.
Then re-implantation of the joint.
what is the clinical picture of necrotising fasciitis?
Highly painful with some signs of inflammation (pain disproportionate to superficial appearances)
Spread through tissues very rapidly
Systemic toxicity
which bacteria is type 1 necrotising fasciitis caused by?
anaerobes plus multiple other bacteria “synergistic gangrene”
which bacteria is type 2 necrotising fasciitis caused by?
“flesh eating bacteria”
group A strep
how is necrotising fasciitis diagnosed?
swabs & tissue biopsy for microbiology & culture
blood cultures
CRP, FBC, clotting factor, U&Es
how is necrotising fascittis treated?
surgical debridement
antibiotics
which antibiotics would you give for necrotising fasciitis caused by strep pyogenes?
penicillin & clinamycin
which antibiotics would you give for synergistic necrotising fasciitis?
piperacillin-tazobactam
clindamycin
gentamycin
which bacteria causes Gas gangrene?
clostridium perfringens (part of normal bowel flora)
describe the microbiology of clostridium perfringens
gram positive strictly anaerobic rods
how is gas gangrene spread
spores into tissues with germinate and crete an accumulation of gas bubbles in tissues
what sign would expect to find on palpation in gas gangrene?
crepitus
what is the treatment of gas gangrene?
urgent debridement in theatre
antibitocs
+/- hyperbaric oxygen
what antibiotics are given for gas gangrene?
penicillin & metronidazole (either or both)
which bacteria causes tetanus?
clostridium tetani
describe the microbioogy of clostridium tetani
gram positve strictly anaerobic rods
where are the spores of clostridium tetani found?
in soil, gardens, animal bites etc.
which toxin is present in tetanus and what does it cause?
neurotoxin causes spastic analysis
how does neurotoxin cause spastic paralysis?
binds to inhibitory neurones, preventing the release of neurotransmitters
what is the incubation period of tetanus?
4 days - several weeks
what symptom is often found in tetatnus?
lock jaw due to muscle spasm
how is tetanus treated?
surgical debridement antitoxin supportive measures antibiotics booster vaccination
what antibiotics can be used in the treatment of tetanus?
penicillin or metronidazole
what type of vaccination is the tetanus vaccine?
toxoid vaccine
which antibiotics can you give for staphs & streps?
flucloxacillin (staph. aureus)
vancomycin (if pen. allergic)
clindamycin (antitoxin)
which antibiotics can you give for coliforms?
gentamycin sometimes ceohalosporins (ceftriaxone) sometimes ciprofloxaxin (oral)
what physical/chemical environmental factors can increase the risk of infection of implanted devices?
low pH
reduced O2
free nucleic acid & other cell products
why would you take at least 3 bone samples for culture in PJI?
Superficial swabs are a waste of time as they reflect the skin flora rather than deep infection
Bone samples can get contaminated with skin flora in theatre (or in the laboratory)
CoNS are normal part of skin flora
is CRP always elevated in infections?
no
especially not in chronic infections
what can CRP levels be influenced by?
underlying diseases
surgery
when can you be sure of clinical cure of PJI?
until at least 2 years after treatment of PJI
what prophylactic antibitotics are give before prosthetic joint or implant surgery?
co-amoxiclav 1.2g peri-op & posto-p doses
pen allergy - co-trimoxazole
