Microbiology Flashcards
G + vs G -
One of the differences between G+ and G- is the cell wall of the bacteria, G+ has a thicker wall and its peptidoglycan component is thicker, G- has a high content of Lipopolysaccharide.
The G+ in violet or blue (as it retains both the crystal violet and safranin) while G -
bacteria when washed with alcohol lose the Crystal violet and retain the safranin (pink)
This is crucial to make a treatment decision
About Staph. aureus?
-G+
-one type of staphylococci
-Cluster (Staph)
-Only Coagulation positive (which appears gold)(wound, skin infection)–>distinguish it from other staph species
-Aerobic but facultatively anaerobic (grows best aerobically (in the air), but also grows anaerobically)
-Antibiotic (i.e. flucloxacillin)
-Two main strains:
MRSA (resistance strain)
MSSA
List some clinical presentations of acute bone and joint infections
Temperature
Pain, redness, swelling
Reduced mobility
Define SIRS
2+ of Temp less than 36 or more than 38 Heart rate more than 90 Resp rate more than 20 PaCO2 less than 4.3kPa WBC more than 12k or less than 4k
What is septic arthritis? How can it be introduced?
Infection of the joint space
Blood spread, direct innoculation or from infected bone
What are the main organisms that cause septic arthritis?
Staph. aureus
Streptococci
List diagnostic investigations for septic arthritis
Blood culture if pyrexial
Blood tests
Joint fluid aspirate for microscopy/culture
USS, XR, CT bone
What is the main empirical treatment for septic arthritis?
empirical treatment given based on experience and experiments
Flucloxacillin (Staph. aureus)
N.B. high-dose IV to maximise uptake
If there is a child under 5yrs old with septic arthritis, which antibiotic should be added and why?
Ceftriaxone for H. influenzae/Kingella cover
How long does antibiotic treatment for septic arthritis usually last?
2-4 weeks
What is osteomyelitis?
Inflammation of bone + their medullary cavity
Classification of osteomyletitis?
Acute vs chronic (time)
Contiguous vs haematogenous (spread)
Host Status: Presence of vascular insufficiency, host susceptibility
Which organisms cause chronic osteomyelitis?
Mycoplasma
Pseudomonas
Salmonella
Brucella (goat’s milk)
Treatment and diagnosis of osteomyelitis is similar to septic arthritis. What is the key difference in terms of treatment length?
4-8 weeks duration of antibiotic treatment
Which organisms cause type 1 necrotising fasciitis?
Mixed anaerobes and other bacteria
Which organism causes type 2 necrotising fasciitis?
Group A Strep. (flesh-eating bacteria)
List the mainstay treatment for necrotising fasciitis
Surgical debridement
Pencillin + clindamycin
What is gas gangrene?
Spores forming in tissue, causing accumulation of gas bubbles
What is tetanus?
Neurotoxin produced by Clostridium tetani prevents release of neurotransmitters, causing locked jaw/spastic paralysis
When is vancomycin used empirically instead of flucloxacillin?
If MRSA, diptherioids, or penicillin-allergic
Why is clindamicin useful?
Antitoxin properties - effective against PVL, group A Strep.
Why do bacteria in biofilms pose a problem?
Resistant to immune system and antibiotics
Why are superficial wound swabs a waste of time?
Reflect skin flora rather than deep infection (coag neg Staph. are part of flora)
Coagulate- positive?
Coagulase is an enzyme which converts fibrinogen into fibrin resulting in clotting; an enzyme that clots the plasma.
