Question

1.Briefly describe the differences between the following culture media? Provide an example each case.
a. selective and differential media.
b. reducing media.
c. complex media.
d. Culture media to isolate Mycobacterium tuberculosis.

2.Describe the effects of the following agents on microbial growth.
a. soap
b. 70% alcohol
c. phenol
d. cationic detergent
e. iodine

Answer 1

1 a) selective media allows the growth of selective organism and inhibits the growth of other organism. Eg eosin and methylene blue media, yeast and mold media.

While differential media contains different indicators within media to distinguish within same species of bacteria.

Example blood agar

1 b) reducing media is for the growth of anaerobic microbes, as this media removes dissolved oxygen from media and creates anaerobic conditions. Example thioglycolate broth.

1 c) complex media are rich in nutrients, contains organic materials such as beef extract, yeast extract, blood or milk. Example tryptic soy agar, nutrient broth.

1 d ) Lownstein jensen is a type of selective media used for the culture of Mycobacterium tuberculosis . This media is incorporated with congo red and malachite green for the growth of unwanted bacteria.

2 a)soap , has antimicrobial activity and inhibits the growth of large number of bacteria as it lowers the surface tension of media without the alteration of hydrogen ion in the media.

2 b) 70% alcohol kills the organism by coagulation of protein and slowly spreads within the whole organism. Thus it can be used as disinfectant.

2 c) phenol, is used as indicator to identify changes from neutral to acidic . In tissue culture it is used as weak estrogen.

2 d) cationic detergent ,detergents are used to increase the surface area of microbes and hence increases the intake of nutrients. Cationic detergent is specific for the growth of some micro organism examples, lactobacillus and inhibits the growth of pseudomonas aeuroginosa.

2 e) iodine can be used as indicator whether starch is hydrolysed in culture media or not along with it is essential micro trace element which enhance the growth of microbes.