2 | Page 8. Eosin Methylene Blue(EMB)media; al inhibits the growth of gram-negat

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2 | Page 8. Eosin Methylene Blue(EMB)media; al inhibits the growth of gram-negative bacteria T or F b) inhibits the growth of gram-positive bacteria T or F c) if an organism ferments, lactose acid is not produced T or F 9. A pH sensitive Dye, in the following media, responds to Acid Production by a change in color (see page 387, Benson's) a] MacConkey agar media turns reddish; T or F bl Eosin Methylene Blue(EMB)agar media produces a green metallic sheen; T or F c] Mannitol-salt agar (MSA) turns yellow; T or F 10. Page 258-259, Brown: Citrate Media is used in the characterization of bacteria. Citrate utilization results in the production 11. What grows on EMB agar? Gram negative bacteria. Therefore, EMB is a source of Gram -) bacteria, which can be used 12. What grows on MacConkey's agar? Gram negative bacteria. This means that EMB is a source of Gram (-) bacteria, which can NOTE: What grows on MSA? Staphylococcus spp., which happens to be Gram (+). This means that MSA is a source of of ammonia, which is alkaline, and turns the pH indicator from blue to green. T or F for Citrate, SIM and other tests that require pure cultures. T or F be used for Citrate, SIM and other tests that require pure cultures. T or F Gram (+) bacteria, which can be used for Citrate, SIM, and other tests that require pure cultures. BACTERIA (Ge )-TGram Stain 75% Blood Agar EMB observations*observations *observations MSA MacConkey nus, spectes -or )data hemolysis 1. Staphylococcus aureus 2. Escherichia coli 3. Bacillus megaterium 4. Serratia marcescens 5. Mycobacterium smegmatis 6. Klebsiella pneumoniae 7. Proteus vulgaris 8. Micrococcus luteus 9. Pseudomonas aeruginosa 10. * OBSERVATIONS: NG-No-Growth, A = Acid Produced, AN = Acid Negative GRAM STAIN DATA: See page 282, Table 39.1, Benson's, Textbooks 2| Page

Explanation / Answer

8. a. False, it slightly inhibits the growth of gram positive bacteria.

8. b. True

8.c. False, Lactic acid is a product of fermentation pathways.

9. a. True, Production of lactic acid by lac + bacteria will lower down the pH below 6.8 hence colonies will look pink.

9.b. True,

9.c. True, if mannitol is used by the bacteria it will produce an acid bye product which will change phenol red color to yellow.

10. True, Bromothymol blue changes color to green at pH above 7.6. the pH rises due to convesrion of citrate to carbonates and biocarbonated and production of ammonia from ammonium salts.

11. False, most types of gram negative will grow on this media hence we are getting a mixed culture. but the tests require pure cultures.

12. False, most gram negative will grow on this media. So we will get a mixed culture. but the tests require pure cultures.

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