Page 605 - The Veterinary Laboratory and Field Manual 3rd Edition

542 Karen Liljebjelke

using blood, dilute the sample 1 : 10 in 9 Sero-grouping of O-group antigens may be
brain-heart infusion broth (BHI), and then performed if the information is required for
streak onto MacConkey agar. autogenous vaccine production, or if the
3 Samples may also be plated onto blood agar information is needed for other purposes.
plates. Dome shaped yellow colonies dis- 10 Antimicrobial sensitivity testing is an impor-
playing alpha or beta haemolysis should be tant ancillary test, as E. coli are inherently
gram stained and tested for identification of resistant to the macrolide class of antibiot-
Staphylococcus aureus. ics, and in general tend to be multi-drug
4 Examine MacConkey agar plate for white resistant, with a high proportion resistant to
to pink colonies, some of which may have the beta-lactams. Disc diffusion is the least
a hazy zone surrounding them. If there are expensive and least technical method for
pink colonies use these for the rest of the antimicrobial sensitivity testing. Methods
diagnostic testing. for creating antibiotic impregnated filter
5 Streak a pink colony onto blood agar and discs in-house are available as a cost-sen-
incubate overnight at 37°C. Colonies from sitive alternative to purchasing ready-made
the blood plate should be used for the gram discs for use in testing.
stain, oxidase and indole tests.
6 Gram stain of colonies should show gram
negative rods. Bibliography
7 The gram negative rods: E. coli, Enterobacter
spp. or Klebsiella spp., are all oxidase test Dho-Moulin, M., Fairbrother, J.M. (1999) Avian patho-
negative. genic Escherichia coli (APEC). Veterinary Research
30(2–3): 299–316.
8 E. coli is indole reaction positive, while Gross, W.B. (1991) Colibacillosis. In: Calnek, B.W.,
Enterobacter spp. and Klebsiella spp. are indole Barnes, H.J., Beard, C.W., Reid, W.M., Yoder, H.W.
negative. (eds) Diseases of Poultry, 9th edn, pages 138–144.
Iowa State University Press, Ames, IA.

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