Microbiology 1 Flashcards
what is osteomyelitis?
inflammation of bone and medullary cavity
usually in ling bones
how can osteomyelitis be classified?
acute/chronic
contiguous/haematogenous spread
host status (e.g presence of vascular insufficiency)
usually the first two
how can osteomyelitis be diagnosed in general terms?
direct (biopsy)
indirect (wound swabs, blood cultures but not as good, cross sectional imaging)
how is osteomyelitis generally treated?
debridement
antimicrobials
- not an emergency unless they have sepsis
what is a diagnostic factor of osteomyelitis
if you can see a tendon
are empirical antibiotics used in osteomyelitis?
NO
not until a biopsy has been performed and you know the specific pathogen (unless they have sepsis)
what causes infection in the bone?
bone is generally resistant to infection so would need to be necrosis of bone or very virulent organism
describe the principles of surgery for osteomyelitis
remove infected tissue
drain
debride
6 weeks of treatment as debrided bone takes 6 weeks to be covered in soft tissue? (can be a variety of treatments i.e - IV then oral)
where does bone infection tend to occur? (6)
- open fractures
- diabetes/vascular insufficiency
- haematogenous osteomyelitis
- vertebral osteomyelitis
- prosthetic joint infection
- specific hosts and pathogens
which staph causes most problems?
coagulase positive coagulase negative (epidermidis) doesn't usually cause problems unless the person has a metal/plastic prosthetic (not virulent)
name 2 appropriate bone cultures
percutaneous aspirate
deep surgical cultures
coagulase +ve vs -ve result in test tube?
+ve clots
how does infection occur in open fractures (bone pierces skin) and give a clinical clue of this?
contiguous infection
non-union of bones
poor wound healing
early management of open fracture infection?
aggressive debridement
when is a diabetic ulcer likely to get infected?
> 2cm for >2 months
is diabetic ulcer polymicrobial?
yes as its rotting flesh
how is diabetic osteomyelitis diagnosed?
bone probe (surface swab not useful as too many bugs present)
how is diabetic osteomyelitis treated?
debridement
antimicrobials
antibiotics after probe so you know
best diagnosis of osteomyelitis and infecting organism?
bone biopsy and culture
best imaging for osteomyelitis?
MRI (X rays can show changes after a long time)
mild, moderate and severe diabetic ulcer treatment?
mild - flucloxacillin
mod - flucloxacillin _ metronidazole
severe - flucloxacillin + metronidazole + gentamicin
how long is treatment maintained for infection?
7 days
14 if blood infection
6 weeks if osteomyelitis
DURATIONS IMPORTANT
vancomycin?
MRSA
gentamicin?
gram -ves
metronidazole?
anaerobes
gram +ve cover?
fluclox (IV)
vancomycin (IV)
doxy (oral switch)
gram -ve cover?
gentamicin (IV)
cotrimoxazole/doxy (oral switch)
anaerobes?
metronidazole
is vancomycin used orally?
not really
only for C. Diff
general endocarditis treatment?
6 weeks IV antibiotics
is pseudomonas in a culture likely to be an infection?
only if its in the blood, sputum or surgical biopsy
probably not if its a skin swab
name some likely coloniser organisms?
pseudomonas E. Coli Proteus Klebsiella Enterobacter Bacillus sp Coagulase -ve staph
name some organisms which are always treated as significant
staph aureus
Group A, B, C strep Milleri strep
Anaerobes
who classically gets haematogenous osteomyelitis?
prepubertal children
IV drug users
people with central lines/dialysis
elderly
sources of haematogenous osteomyelitis?
tonsils skin teeth GI UTI mostly staph aureus
staph aureus blood culture treatment?
minimum 14 days antibiotics
must take lines out if present or look for other source of infection
common types of infection in IV drug users?
contiguous haematogenous direct inoculation Staph aureus most commonly can be in unusual sites
what causes osteomyelitis in sickle cell disease?
staph aureus
salmonella
usually affects long bones but can be multifocal
where does bone infection occur in Gaucher’s disease and what typically causes it?
tibia (can mimic bone crisis)
staph aureus
what is SAPHO and CRMO?
Synovitis Acne Pustulosis Hyperostosis Osteitis
Chronic Reccurent Multifactoral Osteomyositis
can often me mistaken for osteomyelitis as similar symptoms and raised inflammatory markers
excluded via history and culture
how does vertebral osteomyelitis usually occur?
mostly haematogenous can be associated with epidural abscess or psoas abscess or PWID IV infections GU infections SSTI post op
features of vertebral osteomyelitis?
only 50% have fever
90% just have pain and raised inflammatory markers
<50% have raised WCC
few have neurological symptoms
vertebral biopsy?
always biopsy before empirical antibiotics
1st biopsy not as sensitive as the 2nd
open biopsy if still no answer after the 2nd
how is vertebral osteomyelitis treated?
drainage of paravertebral/epidural abscess
antimicrobials for 6 weeks (extended if complicated)
(expect >50% decrease in ESR)
when is MRI repeated?
increasing pain, inflammatory markers or new symptoms
what is Potts disease?
vertebral TB
what are the features of Potts disease?
often no systemic symptoms
skin/soft tissue infection common
wedge shaped spine deformity
risk factors for prosthetic joint osteomyelitis?
rheumatoid arthritis
diabetes
malnutrition
obesity
is pulmonary TB associated with vertebral TB?
not always (<50%)
how can prosthetic joint osteomyelitis occur?
direct inoculation during surgery
manipulation of joint during surgery
seeding of joint at later time (e.g from a bacteraemia)
early vs late prosthetic joint infection?
early = within a month (wound sepsis) late = after 1 month (contamination during surgery)
what is biofilm?
community of bacteria that are very difficult to penetrate with antibiotics
grow slowly covering prosthetic joint
in which disease are severe biofilms found?
CF
prosthetic joint osteomyelitis organisms?
gram +ves - staph aureus - staph epidermidis gram -ves (fungi) (mycobacteria)
how is prosthetic jont osteomyelitis diagnosed?
culture - perioperative tissue (multiple) - if same organism grows from many samples = significant blood culture CRP radiology
how is prosthetic joint infection osteomyelitis treated?
ideally removal of the joint
therapy for 6 weeks
re-implantation of joint after antibiotic therapy (not always possible)
plaktonic vs sessile bacteria?
planktonic = bacteraemia sessile = biofilm, phenotypic transformation of planktonic bacteria
reasons for septic arthritis?
inflammation of the joint space
blood borne organisms
extension of local infection
direct innoculation
bacterial causes of septic arthritis?
staph aureus
strep
coag -ve if prosthetic
Neisseria ghonorrhoea if young and sexually active
how is septic arthritis diagnosed?
clinical features
joint fluid microscopy
blood culture if pyrexial
how is septic arthritis treated?
presumptive flucloxacillin treatment
if <5 add cephtriaxonee
adjust when organisms confirmed
what is chikungunya?
….
can viruses cause septic arthritis?
yes
- hep B
- rubella
- parovirus
- alphavirus
what causes pyomyositis?
90% are staph but can be site specific (i.e perineal infections - think gram -ves)
causes of pyomyositis in temperate and tropical places?
tropical - MSSA
temperate - immunosuppressed (pseudomonas, beta strep, enterococcus)
causes of pyomyositis in IV drug users?
clostridium?
how is PVL noticed?
more sick than you expect
necrotising bacteraemia/pneumonia
invasive infections
what else can cause myositis?
viral - diffuse (HIV, rabies etc)
fungal (rare)
parasites (taenia etc)
what is polymyositis?
inflammatory disease of many muscles in the body causing weakness
what is myonecrosis?
destruction of tissue by infection
what is tetanus?
clostridium tetanis toxin causes disease
gram +ve
strictly anaerobic
spores found in soil, gardens
what does tetanus do?
neurotoxin causes spastic paralysis (by preventing release of neurotransmitters)
locked jaw, muscle spasm
non invasive
inoculation period of tetanus?
4 days - several weeks
diagnosis of tetanus?
culture very hard so usually a clinical picture
how is tetanus treated?
surgical debridement antitoxin supportive measures antibiotics sometimes vaccine available
how are septic patients always treated?
empirically
