Practical 4: Investigation of Gram-negative cocci

Question 1

List the gram negative cocci genus

Answer 1

Neisseria

Moraxella

Question 2

How could you identify Neisseria before carrying out tests
(3)

Answer 2

Seen in pairs

Often kidney shaped cocci

Grown on chocolate agar

Question 3

How could you identify moraxella before carrying out tests
(3)

Answer 3

Cocci in pairs

Tend to resist decolorisation

Grown on chocolate agar

Question 4

List the six clinically significant strains of Neisseria

Answer 4

N. gonorrhoeae

N. meningitidis

N. pharyngitis

N. lactamica

N. flavescens

N. sica

Question 5

What test do you carry out to confirm Neisseria species

Answer 5

Carry out a TAXO sugar utilisation test

Question 6

How do you distinguish Neisseria species?
(2)

Answer 6

Distinguished by growth requirements and sugar utilisation pattern

N. gonorrhoeae and N. meningitidis can only be grown on Chocolate agar

Question 7

What four sugars are used in the TAXO sugar utilisation test?

Answer 7

Glucose

Maltose

Sucrose

Lactose

Question 8

What sugars does N. Meningitidis utilise

Answer 8

Glucose

Maltose

Question 9

What sugars does N. gonorrhoeae utilise

Answer 9

Glucose

Question 10

What sugars does N. flavescens utilise

Answer 10

None

Question 11

What sugars does N. lactamica utilise

Answer 11

Glucose

Maltose

Lactose

Question 12

What sugars does N. sicca utilise

Answer 12

Glucose

Maltose

Sucrose

Question 13

What is the principle behind the TAXO sugar utilisation test?
(2)

Answer 13

Discs containing different sugars, dextrose, maltose, sucrose and lactose are placed on the culture

If the organism results in a drop in pH, upon the addition of phenol red indicator there will be a resulting colour change

Question 14

How do you carry out a TAXO sugar utilisation test
(6)

Answer 14

Ask for a x2 chocolate agar plate, x2 TAXO sugar discs and x2 bijou jar containing sterile water

Prepare a heavy suspension of the test isolate using 5ml sterile water

Lawn the inoculum over the entire surface of a chocolate agar plate

Using sterile forceps place the TAXO discs on the inoculum

Use N. lactamica as your control

Incubate at 37 degrees -> add phenol red after incubation

Question 15

What should you use as your control for TAXO sugar test?

Answer 15

N. lactamica

Question 16

What tests should you carry out to test for Moraxella
(2)

Answer 16

DN’ase test

Catarrhalis disk test

Question 17

What is the principle behind the Catarrhalis disk test?
(2)

Answer 17

This is based on the ability of M. catarrhalis to hydrolyse tributyrin

The Remel Catarrhalis disk test is a reagent impregnated tributyrin hydrolysis disc test for the presumptive ID of catarrhalis

Question 18

How do you carry out the catarrhalis disk test
(3)

Answer 18

Ask for two catarrhalis disc, ask for a M. catarrhalis control

using a sterile wooden applicator to rub several colonies of test or control onto catarrhalis disc

Wait for 2 minutes to observe a colour change

Question 19

What is a positive catarrhalis disc test?

Answer 19

Positive = blue-green colour development

Question 20

What is a negative catarrhalis disc test?

Answer 20

No colour development within 2 mins

Question 21

What DN’ase test result will N. catarrhalis give?

Answer 21

Positve result

Question 22

What feature of catarrhalis can be seen from a colony?

Answer 22

Hockey-puck colonies