Diagnostic Bacteriology Flashcards
How does gram-staining work?
Identifies 2 groups of bacteria:
Gram negative and gram positive
- Application of crystal violet
- Application of iodine- formation of crystal violet and iodine complex
- Alcohol wash- alcohol dehydrates peptidoglycan layer
- Application of safranin- stains pink
What is gram negative bacteria?
Has 2 outer membranes with thin peptidoglycan
Stains pink
What is gram positive bacteria?
has 1 outer membrane with thick peptidoglycan
Stains purple
What shapes can bacteria be?
Spheres= cocci Diplococci- 2 cocci Diplococci encapsulates- 2 cocci encapsulated Staphylococci- many cocci in group Streptococci- many cocci in line Sarcina- 3D cube cocci formation Tetrad- square cocci formation
Cylinders= bacilli Coccobacillus- oval shape Diplobacilli- 2 bacilli palisades- bacilli joined by long side streptobacilli- bacilli in a line (chain)
What does a hemolytic activity growth test show?
Gamma haemolysis= no haemolysis (no zone)
Alpha Haemolysis= partial haemolysis (opaque zone)
Beta haemolysis= complete haemolysis (transparent zone)
How do you carry out a hemolytic activity growth test?
- single colony picked up from agar plate
- streak out bacteria colony on agar plate with 5% sheep RBCs
- Incubate agar overnate and assess haemolytic activity the next day
What does a lactose fermentation growth test involve?
Growth on MacConkey agar containing bile sales, crystal violet and lactose
tests capacity of a microorganism to ferment lactose
What does a lactose fermentation growth test show?
No growth- bile salts inhibit growth of gram-positive bacteria
Lactose fermenting- bacteria produce acid during lactose fermentation
Lactose non-fermenting- bacteria don’t ferment lactose
Difference in acidity is measured to determine if its lactose fermenting
How is a lactose fermentation growth test carried out?
- Pick bacteria colony if agar plate
- Streak out bacteria onto MacConkey agar plate that contains pH indicator (agar is red at neutral)
- Incubate plate overnight and assess in morning
What is a catalase test?
Determines if a bacteria produces catalase- an enzyme that catalyses the breakdown of hydrogen peroxide into O2 and H2O
What does a catalase test show us?
Catalase + = O2 bubbles
Catalase - = no O2 bubbles
How is a catalase test carried out?
- bacteria is applied to a glass slide
- Hydrogen peroxide is applied to bacteria
- Short incubation period then observe for bubbles
What is a coagulase test?
Determines whether a bacteria produces coagulase- an enzyme that cross links fibrinogen to form a clot on bacterial surface
It can determine S. aures (produces coagulase) from other staphylococci ( dont produce coagulase)
What does a coagulase test show us?
Coagulase + = clumps
Coagulase - = no clumps
How is a coagulase test carried out?
- Bacteria applied to slide
- Plasma is applied on top
- This is shortly incubated with gentle rotation
4 Look for clumps
