Example of classifying a bacterium

The above animation provides an example of how a bacteria may be classified, using the techniques mentioned in the previous step.

1. Clinical sample isolated and, on Gram stain, found to be a Gram-positive bacterium of spherical shape, forming chains

   • Now we know its Gram-positive cocci (probably Streptococcus)

2. The next step is to subject it to the catalase test. Is it catalase positive or negative?

   • In this example, the bacterium is catalase-negative, which allows us to classify it as a member of the Streptococcus species.

3. Grow the bacterium on Sheep’s blood agar to determine haemolysis

   • In this example, the isolated bacterium cleared sheep’s blood agar.

End result: We now know that the infectious bacterium is a beta-haemolytic Streptococcus.

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