TODD HEWITT BROTH WITH GENTAMYCIN, NALIDIXIC ACID AND 5% BLOOD

Technical Data #2781a / 2013.06.15

Tood Hewitt Broth with gentamycin, nalidixic acid and blood is a liquid selective medium used to recover Streptococcus group B from vaginal tract. A rapid identification using this selective broth and a slide test with group B antiserum may be done and give positive results, without broth incubation, if the organism concentration is fairly high. Addition of blood shows hemolytic activity of Streptococcus group B.

 


 

FORMULA
in grams per liter purified filtered water

Beef Heart, Infusion

3,1

Casein/Yeast Peptone

20,0

Sodium Chloride

2,0

Disodium Phosphate

0,4

Sodium Carbonate

2,5

Dextrose

2,0

Antibiotics

 

Gentamycin

0,008

Nalidixic Acid

0,015

pH 7,6 +/- 0,2 à 25º C

This approximate formula may be adjusted and/or enriched to obtain best results.


PRECAUTIONS
This medium is for laboratory use only.


STORAGE
Store prepared media at 2-8° C protected from direct light. Medium must not be used if there are signs of contamination or if the expiry date has passed. Store dehydrate powder in a dry place in tightly-sealed containers at 2-25° C. Do not use dehydrated media if expiry date has passed.


DIRECTIONS
Suspend 30 grams in 1000 ml of purified water. Heat gently with frequent agitation and boil for one minute. Sterilize at 121° C for 15 minutes and cool to 45-50° C. Add 1x10 ml of Gentamycin Supplement (8699) and 1x10 ml of Nalidixic Acid Supplement(8631); add 50 ml of defibrinated sheep blood (4245). Mix carefully and dispense aseptically into sterile culture tubes.


PROCEDURE
Bring prepared medium at room temperature before inoculation.

  1. Aseptically, add alginate swab to selective broth and test with A & B antisera by slide agglutination.
  2. If test is negative, incubate for 24 hours at 35° C with 5% CO2.
  3. Retest after incubation or confirm by subculture.


QUALITY CONTROL

Expected results after 24 hrs at 35ºC W 5% CO2

Organisms

ATCC

Growth

Streptococcus agalactiae

13124

+

Streptococcus pyogenes

19615

+

Escherichia coli

25922

-


LIMITATIONS OF METHOD
A positive result without incubation confirm an organism concentration of 107 per ml. If test is negative after 24 hours incubation, confirm by subculture. This is only a part of the identification. Other tests may be required.


REFERENCES

  1. Baker, C.J., D.K. Goroff, S.L. Alpert, C. Hayes, W.M. Mc Cormack. 1976 Comparaison of Bacteriological Methods for the Isolation of Group B Streptococcus from Vaginal Cultures. J.Clin. Microbiol. 4:46-48.
  2. Fenton, L.J., M.H. Harper. 1979 Evaluation of Colistin and Nalidixic Acid in Todd Hewitt Broth for Selective Isolation of Group B Streptococci. J.Clin. Microbiol. 9:167-169.
  3. Jones, D.E., E.M. Friedl, K.S. Kanarek, J.K Williams D.V. Lim. 1983 Rapid Identification of Pregnant Women Heavily Colonized with Group B Streptococci. J.Clin. Microbiol. 18:558-560.
  4. Lennette, E.H. et al. 1985 Manual of Clinical Microbiology 4th ed American Society of Microbiology, Washington
  5. Szilagyi, G., E. Mayer, A. I. Eidelman 1978 Rapid Isolation and Identification of Group B Streptococci from Selective Broth Medium by Slide Co-Agglutination Test. J.Clin. Microbiol. 8:410-412.


CATALOGUE NUMBERS

Dehydrated media 500 g QB-39-4815
     
Prepared media    
Tubes 16x125 mm 10/pkg 2781
Gentamycin Supplement, 10 ml 10/pkg 8699
Nalidixic Acid Supplement, 10 ml 10/pkg 8631
     
Defibrinated Sheep Blood 50 ml 4245

 


 

 

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