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2.2 Microbiology > ID: Streptococci and Enterococci > Flashcards

ID: Streptococci and Enterococci Flashcards

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1
Q

What are the three classifications of streptococci

A

Alpha haemolytic

Beta haemolytic

Gamma haemolytic

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2
Q

What are the basic characteristics for streptococci

A

Could be alpha, beta or gamma haemolyisis

KOH negative

Catalase negative*

Oxidase negative

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3
Q

What tests would you carry out for streptococci?
(6)

A

Lancefield grouping (b) (g)

Bacitracin (b)

Optochin (a)

MacConkey (g)

Bile Aesculin (g)

Vancomycin (g)

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4
Q

What are the basic characteristic test results for enterococci?
(4)

A

Cocci*

Gram positive*

Aerobe*

Catalase negative *

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5
Q

What’s the most important step when identifying streptococci/enterococcus?

A

If you have a gram positive, aerobe, catalase negative cocci, you need to be able to identify haemolysis

Only certain tests carried out for each type of haemolysis

Gamma haemolysis usually means an enterococcus

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6
Q

What are the results of the preliminary ID tests for streptococci?

A

Cocci

Gram positive

Catalase negative

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7
Q

What are the five clinically significant strains of streptococci?

A

Strep pneumonia

Strep pyogenes

Strep viridans

Strep mutans

Strep agalactiae

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8
Q

How can you tell a strep is strep pneumoniae from how is appears on a blood agar plate and under a microscope

A

Alpha haemolysis

Draughtsman colonies or mucoid colonies

Lanceolate -> flame shaped cocci

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9
Q

What strep strains have alpha haemolysis

A

S pneumoniae (most likely)

S viridians

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10
Q

What strep strains have beta haemolysis

A

S pyogenes (most likely)

S agalactiae

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11
Q

What strep strains have gamma haemolysis

A

S. bovis however any gram positive cocci which are catalase negative and don’t have haemolysis are more than likely enterococcus than strep

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12
Q

What four tests are used to speciate streptococci?

A

Optochin susceptibility

Bacitracin susceptibility

MacConkey agar -> bile susceptibility

Lancefield grouping (classifies B-haemolytic strep)

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13
Q

What is the only test needed to speciate alpha-haemolytic strep; S. pneumoniae and S viridans

A

Optochin susceptibility test

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14
Q

What is the principle behind the optochin susceptibility test
(2)

A

This test detects an organism’s susceptibility to the chemical optochin

Optochin tests the fragility of the bacterial cell membrane and causes S. pneumoniae to lyse due to changes in surface tension, as shown by a zone of inhibition around the optochin disc

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15
Q

How do you carry out an optochin susceptibility test
(7)

A

Ask for blood agar, optochin disk x3, bijuo jar of sterile water and a swab x3

Divide a blood agar into three section, half for your test and two quarters for positive and negative control

Prepare a suspension of test organism and controls using a reduced volume of sterile water

Lawn inoculate your test and controls

Place one optochin disc in centre of test inoculum and the controls

Incubate overnight at 37 degrees

Examine for a zone of inhibitions

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16
Q

What is your positive control for optochin susceptibility, i.e which strep species is susceptible to optochin?

A

Streptococcus pneumoniae

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17
Q

What is your negative control for optochin susceptibility, i.e. which strep species is resistant to optochin

A

Streptococcus viridans

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18
Q

What three tests must be carried out for B-haemolytic strep

A

Lancefield grouping

Bacitracin susceptibility test

Ability to grow on MacConkey agar

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19
Q

What is the principle behind the lancefield grouping test
(4)

A

The majority of pathogenic strep possess specific carbohydrate antigens, which permit the classification of strep into groups

Strep group antigens can be extracted from bacterial cells and their presence demonstrated with latex particles previously coated with group-specific antibodies

These latex particles will agglutinate in the presence of homologous antigen, but will remain in smooth suspension if absent

The use of enzymatic extraction procedure considerably shortens the time required for antigen extraction and much improves the antigen yield

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20
Q

What is the Lancefield grouping test kit called

A

Oxoid Streptococcal Grouping Kit

21
Q

How do you prepare your bacteria for the Lancefield agglutination test?
(4)

A

Dispense 0.4ml of Oxoid Streptococcus Extraction Enzyme into a labelled test tube

Select 2-5 test colonies and emulsify in the enzyme preparation

Incubate for 10 minutes at 37 degrees Celsius in a water bath -> make sure to shake vigorously at 5 mins in

Remove and allow to cool to room temp

22
Q

How do you carry out the Lancefield grouping test
(6)

A

Ask for a reaction card, sticks, latex reagent A, B, C, D, F and G,

Ask for S. pyogenes or Enterococcus control?

Ask for (pre-mixed?) enzyme (and test) extract??? -> don’t know if this will be done for you previously or you will have to do it yourself

Add 1 drop of latex reagent A, B, C, D, F, G to a circle on your reaction card

Look for agglutination

Carry out this test using the positive control first so you know the reagents are working

23
Q

What does a Lancefield group A indicate?

A

Streptococcus pyogenes

24
Q

What does a Lancefield group B indicate?

A

Streptococcus agalactiae

25
Q

What does Lancefield group C indicate?

A

Streptococcus equi (most probable)

Streptococcus epidemicus

Streptococcus equisimilis

26
Q

What does Lancefield group D indicate?

A

Streptococcus bovis

Or the more probable Enterococcus -> E. faecalis

27
Q

What does Lancefield group F indicate?

A

Streptococcus anginosus

28
Q

What does Lancefield group G indicate?

A

Streptococcus canis

Streptococcus dysgalactiae

29
Q

Which are the most significant Lancefield grouping?
(4)

A

Group A = Strep pyogenes

Group B = Strep agalactiae

Group C = Strep equi or strep equisimilis

Group D = Enterococcus faecalis or Strep bovis

30
Q

What is the principle behind Bacitracin susceptibility
(2)

A

Used to speciate group A, Beta haemolytic strep i.e. to confirm S. pyogenes

Group A strep are sensitive to bacitracin while other groups of strep are resistant

31
Q

How do you carry out a Bacitracin susceptibility test?
(6)

A

Ask for blood agar, x3 bijou jars full of sterile water, and x3 bacitracin discs

Divide a blood agar plate into three sections, one for test, two for controls

Prepare a suspension of test and controls using a reduced volume of sterile water

Lawn inoculum of test and controls

Place one bacitracin disc in the centre of each inoculum

Incubate overnight at 37 degrees

32
Q

What is your positive control for bacitracin, which organism is susceptible for bacitracin?

A

Strep pyogenes is susceptible

33
Q

What is your negative control for bacitracin, which organism is resistant for bacitracin?

A

Use an enterococcus e.g. E.Coli

34
Q

What is the principle behind MacConkey agar?
(5)

A

A selective and differential culture medium

Crystal violet and bile salts make it selective for Gram-negative and enteric (normally found in the intestinal tract) bacteria

Differential based on lactose fermentation.

Lactose fermenters turn red or pink on MacConkey agar, and nonfermenters do not change color.

The media detects lactose fermentation by enteric bacteria with the pH indicator neutral red.

35
Q

What is your positive control for MacConkey agar?

A

Enterococci e.g. E. faecalis

36
Q

What is your negative control for MacConkey agar?

A

Streptococcus e.g. S. pyogenes

37
Q

What is a positive result for MacConkey?

A

Growth

38
Q

What is a negative result for MacConkey?

A

No growth

39
Q

Which Lancefield group will grow on MacConkey

A

Group D -> Enterococcus

40
Q

What should you do if none of your tests confirm species of Strep?

A

Say what it isnt

Say what it could be

Suggest biochemical testing

41
Q

Which are the only Strep you can ID?
(4)

A

Strep pyogenes (Lancefield A)

Strep pneumoniae (positive optochin)

Strep viridans (negative optochin)

Strep agalactiae possibly -> if B-haemolytic strep but not Lancefield A

42
Q

What tests do you carry out to speciate enterococcus?
(5)

A

MacConkey Agar (confirm enterococcus and not strep)

Lancefield (Group D confirms enterococcus and not strep)

Chromogenic VRE Medium

Bile Aesculin Agar

Vancomycin

43
Q

What is the principle behind bile aesculin agar?
(4)

A

A selective and differential agar used to identify members of the Enterococcus genus

Bile salts are selective for Enterococcus

Aesculin is differential -> enterococcus hydrolyse aesculin to form aesculetin and dextrose

Aesculetin combines with ferric citrate in the medium to produce insoluble iron salts, resulting in the blackening of the medium which is a positive result

44
Q

How should you carry out a bile susceptibility test?

A

Ask for a bile aesculin agar plate, E.Coli + control, Strep pyogenes negative control

Spot inoculate

Incubate at 45 degrees !!!!

45
Q

What is a positive bile aesculin test?

A

Blackening of the medium

46
Q

What are the three clinically significant species of Enterococcus

A

E. faecalis

E. faecium

E. durans

47
Q

Explain how to use chromogenic VRE medium

A

This isn’t in the lab note???

Chromogenic Vancomycin Resistant Enterococcus medium

Specific and selective chromogenic medium for the detection and differentiation of Enterococcus faecium and E. faecalis showing acquired Vancomycin resistance (VRE

E. faecalis = bluish green

E. faecium = violet

48
Q

What should you do if you ID an enterococcus?

A

Suggest biochemical testing

Suggest vancomycin susceptibility as some strains are resistant

Suggest chromogenic VRE Medium

2.2 Microbiology (60 decks)

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