Diagnostic Bacteriology Flashcards
What kind of diagnosis at the clinic
Patient history
Patient examination of signs and symptoms
What other non microbiological investigation
Radiology
Haematology
Biochemistry
What laboratory investigations
Microbiological tests
Immunological tests
Molecular biology tests
What kind of sample?
Saliva, blood, urine, faeces
Sputum, cerebrospinal fluid
Tissue, biopsies and pus
Why is diagnosis needed
Treatment of infection Long term complications Prevent transmission and further cases Prevent outbreak Reduce use of antibiotics
What is microscopy based investigation
Gram stain
What do gram negative bacteria have and colour
2 outer membranes with thin peptidoglycan
Pink
What is gram positive and colour
1 outer membrane with thick peptidoglycan
Purple
What is the process of the gram stain
Application of crystal violet
Application of iodine
Alcohol wash - decolorisation
Application of safranin - counter stain
What are coccus and what are bacillus
Spheres and round ended cylinders
What is a culture based investigation
Haemolytic activity
Lactose fermentation
What does this test
Capacity of microorganism to produce haemolysis
Type of hemolysis
Gamma - hemolysis === no hemolysis no zone
Alpha - hemolysis === partial hemolysis opaque zone
Beta - hemolysis === complete hemolysis transparent zone
What is the process for testing for lactose fermentation
Growth on McConkey Agar containing bike salts, crystal violet and lactose
Assess fermentation after overnight incubation
What does lactose fermentation test
The ability of bacteria to ferment lactose
The results from lactose fermentation
No growth - bile salts inhibit growth of gram positives ( exclude the gram positives then)
Lactose fermenting - bacteria produce acid during lactose fermentation pink
Lactose non fermenting - non ferment lactose yellow
What are blood Agar plates used for
Haemolytic activity - further to classify gram positiv bacterial species
What are other Agar plates used for
Assess lactose fermentation
Classify gram negative bacteria
What is the catalase test
Determines whether bacteria produce catalase
(Enzyme that produces hydrogen peroxide) staphylococci (catalase positive)- produced by bacteria which are aerobes
Streptococci (catalase negative) -
What does catalase positive and catalase negative mean
Positive water and oxygen
Negative just water no bubbles
Method for catalase test
Apply bacteria into glass slide
Application of hydrogen peroxide
Observe reaction
What does the test for coagulase determine
Whether a bacteria produces coagulase that cross links fibrinogen in plasma to form a clot on bacterial surface.
What does the coagulase test
It can discriminate s. aureus (produce coagulase) and other staphylococci (do not produce coagulase)
Where is coagulase used with fibrinogen
Prothrombin uses coagulase to produce thrombin
Which forms fibrin to produce fibrinogen
And factor XIIIa forms fibrin clot from fibrin
Describe the process of the coagulase test
Put a droplet of water on unused slide Apply bacteria on glass slide Application of plasma Incubate for 15 seconds and gently rotate Generation of clumps
