Diagnostic Bacteriology

Question 1

What kind of diagnosis at the clinic

Answer 1

Patient history

Patient examination of signs and symptoms

Question 2

What other non microbiological investigation

Answer 2

Radiology
Haematology
Biochemistry

Question 3

What laboratory investigations

Answer 3

Microbiological tests
Immunological tests
Molecular biology tests

Question 4

What kind of sample?

Answer 4

Saliva, blood, urine, faeces
Sputum, cerebrospinal fluid
Tissue, biopsies and pus

Question 5

Why is diagnosis needed

Answer 5

Treatment of infection
Long term complications 
Prevent transmission and further cases 
Prevent outbreak 
Reduce use of antibiotics

Question 6

What is microscopy based investigation

Answer 6

Gram stain

Question 7

What do gram negative bacteria have and colour

Answer 7

2 outer membranes with thin peptidoglycan

Pink

Question 8

What is gram positive and colour

Answer 8

1 outer membrane with thick peptidoglycan

Purple

Question 9

What is the process of the gram stain

Answer 9

Application of crystal violet
Application of iodine
Alcohol wash - decolorisation
Application of safranin - counter stain

Question 10

What are coccus and what are bacillus

Answer 10

Spheres and round ended cylinders

Question 11

What is a culture based investigation

Answer 11

Haemolytic activity

Lactose fermentation

Question 12

What does this test

Answer 12

Capacity of microorganism to produce haemolysis

Question 13

Type of hemolysis

Answer 13

Gamma - hemolysis === no hemolysis no zone
Alpha - hemolysis === partial hemolysis opaque zone
Beta - hemolysis === complete hemolysis transparent zone

Question 14

What is the process for testing for lactose fermentation

Answer 14

Growth on McConkey Agar containing bike salts, crystal violet and lactose
Assess fermentation after overnight incubation

Question 15

What does lactose fermentation test

Answer 15

The ability of bacteria to ferment lactose

Question 16

The results from lactose fermentation

Answer 16

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

Question 17

What are blood Agar plates used for

Answer 17

Haemolytic activity - further to classify gram positiv bacterial species

Question 18

What are other Agar plates used for

Answer 18

Assess lactose fermentation

Classify gram negative bacteria

Question 19

What is the catalase test

Answer 19

Determines whether bacteria produce catalase
(Enzyme that produces hydrogen peroxide) staphylococci (catalase positive)- produced by bacteria which are aerobes
Streptococci (catalase negative) -

Question 20

What does catalase positive and catalase negative mean

Answer 20

Positive water and oxygen

Negative just water no bubbles

Question 21

Method for catalase test

Answer 21

Apply bacteria into glass slide
Application of hydrogen peroxide
Observe reaction

Question 22

What does the test for coagulase determine

Answer 22

Whether a bacteria produces coagulase that cross links fibrinogen in plasma to form a clot on bacterial surface.

Question 23

What does the coagulase test

Answer 23

It can discriminate s. aureus (produce coagulase) and other staphylococci (do not produce coagulase)

Question 24

Where is coagulase used with fibrinogen

Answer 24

Prothrombin uses coagulase to produce thrombin
Which forms fibrin to produce fibrinogen
And factor XIIIa forms fibrin clot from fibrin

Question 25

Describe the process of the coagulase test

Answer 25

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