Question

You have been told to obtain a sputum sample and to perform microbiological staining in order to determine the identity of the pathogen causing a patient’s illness. You first perform a Gram stain, but upon microscopic analysis you visualize a mixture of pink and purple bacilli. Explain the results you have just observed, and discuss what you may now do in order to identify the pathogen.

Answer 1

Microscopic analysis showed a mixture of pink and purple bacilli, it means that in the sputum of a patient, both gram positive and gram negative bacilli are found. The pink colored bacteria are gram negative, and the purple color is gram positive.

The further identification of the pathogen is made using a streak plate method. This method allows us to isolate the single colony of the bacterium.

Further growing of these single colonies into different media and performing their biochemical test can help us to identity the disease causing bacteria.