Microbiology Flashcards
What are the 2 most common causative pathogens of acute osteomyelitis?
MSSA (top) Strep Organisms (eg GAS)
What are coliforms?
groups of organisms which live in bowel normally
What antibiotic switches off the production of PVL in Staph aureus? (MSSA/MRSA)
clindamycin
What are the 2 most likely pathogens for infections of prosthetic joints?
Coagulase negative Staph
Proprionobacteria (diptheroids)
What substance do both coagulase neg staph and proprionobacteria produce that allows them to infect prosthetic limbs?
thick sticky biofilm
What is septic arthritis?
infection of the joint space
What is osteomyelitis?
inflammation (or infection) of the bone + medullary cavity
Why should you take cultures in the diagnosis of acute septic arthritis?
to target treatment to the specific organisms grown
What is the purpose of doing microscopy on the joint fluid aspirate of a patient with suspected acute septic arthritis?
to look for:
- WBC (which shouldn’t be there under normal circumstances)
- crystals (which suggests gout)
- gram stain
What is the empiric treatment for acute septic arthritis for a patient over 5 years old?
flucloxacillin
covers MSSA which is most likely
What is the empiric treatment of acute septic arthritis for a patient under 5 years old?
flucloxacillin (covers MSSA) \+ ceftriaxone (covers kingella/ haemophilus influenzae)
Why do patients rarely present with Haemophilus Influenza B?
vaccination program
Why does flucloxacillin given for the empirical treatment of acute septic arthritis, need to be given IV?
because patients can’t tolerate the high doses needed orally
What are the 2 most common causative pathogens of septic arthritis?
MSSA
streptococci
What are the 3 ways that organisms causing septic arthritis are introduced into the joint space?
- haematogenous spread (blood)
- contiguous spread (eg primary osteomyelitis)
- direct innoculation (eg injection/trauma)
What are the most common causative pathogens of chronic osteomyelitis?
Mycobacterium tuberculosis Pseudomonas aeruginosa Salmonella Brucella Coliforms
What organism is associated with chronic osteomyelitis in patients with sickle cell disease?
Salmonella
What bones are more likely to get osteomyelitis?
long bones
vertabrae
What organism is associated with chronic osteomyelitis in patients drinking unpasteurised goats milk?
Brucella
What are the 4 ways that organisms causing osteomyelitis are introduced into the bone?
- haematogenous (blood) [most likely]
- contiguous spread (eg primary septic arthritis)
- peripheral vascular disease associated
- prosthesis associated
What is the time frame of acute osteomyelitis?
few days to 2 weeks
anything longer is chronic
How long should patients with acute septic arthritis be treated with antibiotics?
2-4 weeks
what joints are more likely to be affected by osteomyelitis?
ie get a secondary septic arthritis
shoulder
elbow
hip
ankle
why are the shoulder, elbow, hip and ankle likely to be affected by osteomyelitis?
because the metaphysis of bones are intracapsular so may extend into the joint space
why are infants more at risk of getting septic arthritis secondary to acute osteomyelitis?
because certain metaphyses are intra-articular so infection can spread to the joint
Why can you wait until the culture results for antibiotic treatment in chronic osteomyelitis?
because there is no SIRS
What is the empiric treatment of acute osteomyelitis?
high dose flucloxacillin
IV
What is the antibiotic treatment length of acute osteomyelitis?
4-8 weeks
what is the aim in antibiotic treatment of acute osteomyelitis?
to stop progression into chronic infection
what are the 4 main risk factors for getting an infection in a prosthetic joint?
- rheumatoid arthritis
- diabetes
- malnutrition
- obesity
How many types of implant infection are there?
3
What is the type of implant infection which occurs 0-3 months after the operation?
early postoperative implant infection
What is the route of infection in an early postoperative implant infection?
perioperative
What are the signs of an early postoperative implant infection?
fever, effusion, warmth, drainage
What are the 3 main causative organisms of early postoperative infection?
Staph aureus
Streptococci
Enterococci
What is the type of implant infection which occurs 3-24 months after the operation?
Delayed (low grade) implant infection
What is the route of infection in a delayed implant infection?
perioperative
What are the signs of a delayed implant infection?
persistent pain
device loosening
fistula
What are the 2 main causative organisms of a delayed implant infection?
Coagulase-neg Staph
P. acnes
What is the type of implant infection which occurs over 24 months after the operation?
Late implant infection
What is the route of infection in a late implant infection?
haematogenous
What are the 2 main causative organisms of a late implant infection?
Staph aureus
E. coli
Why are prosthetic joint infections hard to diagnose?
often caused by organisms which are common contaminents
rarely have a positive blood culture
What is necrotizing fasciitis?
an uncommon but acute and severe infection of the subcutaneous soft tissue
what is the difference between cellulitis and necrotizing fasciitis?
cellulitis stays confined to the subcutaneous tissue, necrotizing fasciitis doesn’t so causes necrosis
What type of pain is typical in necrotizing fasciitis?
pain which is disproportional to what can be seen on the skin
What are the two types of necrotizing fasciitis?
type 1:
anaerobes plus multiple other bacteria (synergistic gangrene)
type 2:
GAS
+/-staph aureus
What is the treatment of necrotizing fasciitis?
surgical debridement
antibiotics
What is the main antibiotic treatment for type 1 necrotizing fasciitis?
clindamycin + gentamycin + others
high level, broad spectrum
What is the main antibiotic treatment for type 2 necrotizing fasciitis?
penicillin + clindamycin
which necrotizing fasciitis is more common- type 1 or 2?
type 1: anaerobes plus others
What bacteria causes gas gangrene?
Clostridium perfringens
part of normal bowel flora
describe Clostridium perfringens?
gram positive, strictly anaerobic rods which produce spores
Why can you feel crepitus in a patient with gas gangrenes?
accumulation of gas bubbles in tissue space
What is the treatment of gas gangrene?
surgical debridement
high dose antibiotics (penicillin and/or metronidazole)
hyperbaric oxygen
What bacteria causes tetanus?
Clostridium tetani
What causes the spastic paralysis in tetanus?
the neurotoxin produced
bacteria is non-invasive, all toxin related
What is the treatment of tetanus?
surgical debridement antitoxin supportive measures antibiotics (penicillin and/or metronidaxole) booster vaccination (toxoid)
If patient is penicillin allergic, what is the best antibiotic to use for a Staph or Strep infection?
vancomycin
If patient has a MRSA infection, what is the best antibiotic to use?
vancomycin
What antibiotics should be used for a coliform infection?
gentamicin
sometimes ceftriaxone or ciprofloxain
What type of antibiotic is gentamicin?
aminoglycoside
what are the 2 serious side effects of long term gentamicin use?
ototoxic
nephrotoxic
What is the only oral available agent for pseudomonas aerginosa?
ciprofloxacin
What is the serious side effect of cephlasporins such as ceftriaxone?
C. dif risk
what is the serious side effect of ciprofloxacin?
C. dif risk
What is the main con of ceftriaxone use in MSK infections?
once daily slow IV infusion
What is the main pro of ciprofloxacin use in MSK infection?
can be taken orally
What protection does biofilm give to bacteria?
protects from immune system and antibiotics
what is the general pH of slime?
low pH (about 5)
What are the 2 types of surgical debridement of a prosthetic joint infection?
- retention of prosthesis (debridement and implant retention- DAIR)
- removal of prosthesis
What is the 3 step Tayside Protocol for prosthetic joint infection?
- no antibiotic pre-op
- minimum 3 bone/tissue/pus samples for culture
- 6 minimum weeks antibiotics before clean surgery
In the tayside protocol for prosthetic joint infections, what is the antibiotic of choice for gram positive infection?
flucloxacillin
In the tayside protocol for prosthetic joint infections, what is the antibiotics of choice for MRSA or penicillin allergic patients with gram positive infections?
vancomycin
then teicoplanin when patient is stabilised
In the tayside protocol for prosthetic joint infections, what is the antibiotic of choice for gram negative organisms?
ciprofloxain
ceftriaxone
(cotrimoxazole
amoxicillin)
what is the duration of antibiotic treatment for prosthetic joint infection?
12 weeks
knee 24 weeks
What bacteria mutc you screen for before undertaking prosthetic surgery?
MRSA
If a patient about to undergo prosthetic surgery is screened and MRSA is found, what is done?
operation is pus on hold,
patient is decolonised using antibiotic nose and body cream for 5 days- screen again
who is more prone to osteomyelitis?
immunocompromised
those with chronic disease
extremes of age
why are children more likely to get osteomyelitis?
because the metaphyses of long bones contain abundant tortuous vessels with sluggish flow allowing the accumulation of bacteria
why can infants get abscesses which extend widely along the subperiosteal space?
because the periosteum in infants is only loosely applied
what is a Brodie’s abscess?
where the bone reacts by wailing off the abscess with a thin rim of sclerotic bone
a more sub-acute presentation of osteomyelitis
-occurs in children
in adults, what bones does chronic osteomyelitis tend to affect?
axial skeleton (spine or pelvis)
where does TB most commonly cause infection? + through what spread?
spine through haematogenous spread from primary lung infection
where is the location that poorly controlled diabetics, IV drug abusers and other immunocompromised patients are at particular risk or osteomyelitis?
spine (particularly lumbar spine)
