Question

30. The most effective means of sterilization is _________________________.

31. Are commercially canned foods sterile?

32. What is the most important organism to eliminate from canned foods?

33. What kind of organism stains with the Ziehl-Neelsen method?

34. What is the primary dye in the stain mentioned in the prior question?

35. What is the color of an organism that retains the primary dye?

36. Name a species that will stain with the primary dye in this stain?

37. What is the decolorizing agent in this stain?

38. What is the counterstain in this stain?

39. Name 3 uses for solid media.

Answer 1

30. Heat sterilization.

Explanation: It is the most effective type of sterilization and it is also called autoclaving. In this a pressurized steam is used for heating the substance to be sterilized. This sterilization method will kill all the microbes, viruses and even the spores.

31. The canned foods are sterilized by autoclaving for about 20 mins at 121oC.

32. Clostridium botulinum is the bacteria which should be eliminated from the canned food because it releases toxin in an oxygen-free environment of a sealed can. This toxins causes botulism.

33. The acid-fast organisms are stained used Ziehl-Neelsen stain. Acid-fast organisms resist the decolorization by acids. The acid-fastness of the acid-fast bacteria is due to the presence of mycolic acid in the cell wall.

34. The primary dye used in Ziehl-Neelsen staining method is carbol fuchsin.

35. The acid-fast bacteria resists the decolorization by acids. Hence, the acid-fast organisms will retain the color of the primary dye and the non-acid fast bacteria will loose the stain after washing with acid.

36. Examples of bacteria which will retain the color of primary dye belongs to the species Mycobacteria. Mycobacteria contains high amount of mycolic acid in the cell wall and hence, they resist decolorization by acid during staining. Therefore Mycobacteria are considered as acid-fast bacteria.

37. The decolorizing agent used in Ziehl-Neelsen staining method is an acid alcohol (3% HCL in 95% alcohol).

38. The counter stain is methylene blue. The non acid-fast bacteria will appear in blue color under microscope.

39. The main uses of solid media are as follows:

a) For isolating pure bacteria from a mixed bacterial culture.

b) For determining the colony forming units

c) For determining the colony characteristics of a bacterial isolate

d) Some solid media are as a selective and differential media for identification of bacteria.