Question

1.) You are asked to prepare a gram stain from a mixture of gram positive and gram negative bacteria during lab. What would happen if you remembered all steps.... except to decolorize – what color would the Gram (+) and Gram (-) be? except to add safranin – what color would the Gram (+) and Gram (-) be?

2.) The organism Yersinia pestis causes the plague, which caused a pandemic in Europe. What test reults would you expect to observe if samples from a plague patient were analyzed using the gram stain, the endospore stain, the capsule stain, and the acid-fast stain? Include the expected shape of the cell, the color Y. pestis cells should turn for each stain, and if the result is positive or negative.

Answer 1

1. There will be purple colour only for both because alcohol is added for decolourisation. Due to which the bacterial cell wall (gram negative )cannot break and washed out . In second case where saffranin is not added that is the last step so that the gram-positive will be purple where as gram negative will have no colour. Because saffranin gives colour to gram negative bacteria after decolourisation.

2. By performing gram stain yersinia pestis gives pink colour because it is gram negative so by decolourising agent alcohol the thin cell wall ruptures by adding saffranin it turns pink.The shape is rod shape.In capsule stain by watching under microscope if they are present look by having black with no cells visibility.But dead cells can be visible in form of purple that is capsule stain the result is negative.Green in colour during endospore staining because of no endospore.Therfore malachite green.is a dye used for staining (endospore).Acid fast stain is negative and the colour of result is positive that the cells turn pink in colour.