Question

3. A. For what suspected disease(s) would the acid-fast stain be performed? B. Why is the acid-fast stain necessary to stain the etiologic agents of that/those disease(s)? 1point

4. Juan is a new lab tech who needs to inoculate agar slants that students will be using to make endospore stain smears. He inoculates the tubes on Monday for a lab the following day. Did the students find endospores on their slides? Explain why or why not. 1 point

5. After inoculating with her unknown, Letitia’s Phenyl Red Glucose, Lactose, and Sucrose tubes are all yellow. Her TSI tube results are K/H2S. The EMB plate result is +/+. Do all results agree? Explain why, or why not. Be thorough! 1 point

Answer 1

3, Acid fast staining is done for diseases for which the causative agent is bacteria belonging to Mycobacterium. The diseases such as tuberculosis, leprosy are caused by Mycobacterium spp.

The mycolic acid and greater amount of lipid and fatty acid makes it impermeable for other stains to get inside the bacteria. So acid fast staining is used in which the primary stain carbol fuschin penetrates the cell wall by solubilising the lipids. Heating also aids in addition to primary stain to solubilise lipids.

4, no, they will not be able to find the endospores because, bacteria produces spores only during adverse conditions since the lab tech has provided nutritients for the bacteria and has only inoculated for a day or two, it is not possible to see the endospores.

5, No there is a confusion in the result between Phenol red test, carbohydrate fermentation test and TSI. The yellow colour formation in phenol red and CHO fermentation test indicates that the organism can ferment sugars thus producing acidic end product but in TSI the result is K- means alkaline end product which is not possible. TSI or triple sugar iron test is also done to check if the bacteria can ferment or not.

So the results do not coincide- mistake in the test done most probably mistake in TSI result because the growth in EMB plate is positive (EMB is a selective media where lactose fermenting Gram negative bacteria grows)

So all the results do not agree!