Investigating Infections I & II Flashcards
Why is it useful to identify a causative agent?
What are the different ways you can carry out microbiological investigation?
How do you identify pathogens?
What does successful microbe identification depend on?
What are the 3 ways you can culture specimens?
What are the different haemolysis on blood agar plates?
Define the terms: differential, selective and enriched media and give examples
They are all types of growth medium
Differential - distinguish one microorganism from another growing on the same plate - haemolysis on blood agar can differentiate bacteria
Selective - contains nutrients to allow selective organisms to grow (e.g. MacConkey’s plate)
Enriched media - contains nutrients which allow for a wide variety to grow
Define alpha and beta haemolysis
Haemolysis = breakdown of blood cells
Alpha haemolysis = incomplete breakdown - green/brown tinge around the bacterial colonies (oxidised blood)
Beta haemolysis = complete breakdown - leaves clear area around bacteria colony
Define lactose fermenter and anaerobe
Lactose fermenter = The process by which bacteria breakdown the sugars in foods and form lactic acid
Anaerobe = microorganisms that grow without oxygen
What are blood cultures?
Explain the value of blood agar and MacConkey’s agar in bacterial identification
Blood agar = an enriched bacterial growth medium that can grow difficult to grow bacteria
MacConkey’s agar = selective and differentialculture medium forbacteria - selectively isolateGram-negative and enteric bacteria and differentiate them based onlactose fermentation (turn red or pink)
Explain the relationship between bacterial numbers in a urine specimen and urinary tract infections
List commensal organisms commonly found in: naso-pharynx, skin, gut, vagina
Naso-pharynx - Staph aureus
Skin - Staph epidermidis
Gut - E coli
Vagina - Lactobacillus
What is the aim of MIC and when would you do it?
Minimum inhibitory concentration
To measure the lowest concentration of antibiotic that inhibits visible growth of the bacteria on a plate (or in liquid culture using dilutions of antibiotics & looking for growth)
Used when:
- Patients are failing to respond to apparently appropriate antibiotic therapy
- When disc diffusion test are not reliable enough
When is the direct antibiotic susceptibility testing performed and on which specimens?
when microscopic analysis of a specimen reveals ad
