LAB EXCERCISES: #18#51#52#53-Differential Media Plates . PURPOSE (OBJECTIVE): To

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LAB EXCERCISES: #18#51#52#53-Differential Media Plates . PURPOSE (OBJECTIVE): To observe and characterize bacteria based on their growth on selective and differential media. Observations are recorded as macroscopic observations. EQUIPMENT/TOoLS/MEDIA/ORGANISMS: - Salt Agar (MSA) Plates, MacConkey Agar (MAC)Plates, Blood Agar Plates, Simmons Citrate agar slant Tubes, SIM Agar Stab Tubes, Nutrient Broth (NB)cultures: Staphylococcus aureus, Escherichia coli, Bacillus megaterium, Serratia marcescens, Mycobacterium smegmatis, Klebsiella pneumoniae, Proteus vulgaris, Micrococcus luteus, Pseudomonas aeruginosa Nutrient Agar (NA)plates, Eosin Methylene Blue (EMB)Agar Plates, Mannitol RESULTS (notes, observations attached), Incubation Temperature incubation Period . ANSWER THE FOLLOWING QUESTIONS: 1. Differentiate between Complex & Defined media. 2. MSA is a selective and differential media. What is a selective media? 3. MSA is a selective and differential medium. What is a differential media? 4. Mannitol-salt agar (MSA) is a selective and a differential medium; a] Staphylococcus aureus grows on MSA and produces acid. T orF bl Staphylococcus aureus grows on MSA but does not produce acid. T or F c) Staphylococcus epidermidis grows on MSA and produces acid. T or F d) Staphylococcus epidermidis grows on MSA and does not produces acid. T or F 5. What components of MSA make it a Selective media? 6. MSA is used for the Isolation and Characterization of which organisms (Genus, species)? 7. MacConkey media; al inhibits the growth of gram-negative bacteria. T or F inhibits the growth of gram-positive bacteria. T or F 1 I Page

Explanation / Answer

1. Complex media has crude nutrient sources; hence its chemical composition cannot be exactly defined. This is the type of media commonly for routine microbial culturing. Eg Nutrient broth

Defined media (is also called synthetic media) has its exact composition known and is used Specific studies. Eg Minimal salt medium

2. Selective media is the type of media in which only certain genus of bacteria can grow. The media will contain certain chemicals that will permit only certain type group of bacteria to grow. MSA has high salt (sodium chloride) concentration and will only allow the growth of those bacteria which can tolerate high salt enviorment.

3. DIfferential media help to distinguish between closely related bacteria, biochemically. MSA can distinguish Staphylococcus aureus and staphylococcus epidermis because former can ferment mannitol and will turn the media from red to yellow while the latter cannot.

4. a. True

b. false

c. false

d. true

5. High salt concentration makes MSA a selective medium, since high salt concentration will let the growth of only salt tolerant microbes.

6. a . Staphylococcus aureus b. Staphylococcus epidermis

7. Macconkey agar medium allows the growth of gram negative bacterium

a. False

b. True

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