LAB3 Culture Media Preparation PDF

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Laboratory Report

18 Student:Kim Collete G.

Date: 02/15/21 Section: BSN-1D

18 Culture Media Preparation A. Short-Answer Questions 1. Differentiate between complex and defined media.

The precise composition of defined media is known, while complex media are not known. For rich extracts of meat or plants, complex media are usually produced. By individually measuring all components, defined media are made. 2. Name six basic nutritional requirements supplied in all culture media.

In all cultural media, essential nutritional requirements include a source of carbon, an energy source, phosphorus, minerals, vitamins, growth factors, and water. 3. What growth factor is often supplied for cultivation of fastidious bacterial pathogens?

The growth factor that is often supplied for cultivation of fastidious bacterial pathogens is “Blood.” 4. A powdered complex medium can be stored for months in the laboratory. However, after preparing the medium, it must be sterilized almost immediately. Why?

Since powdered media lacks water, there can be no microbe growth. It must be sterilized to stop microbial growth after water is applied to prepare the media. 5. An autoclave is typically used for sterilization of media. a. Define sterilization.

It is a destruction of all microbes including bacterial endospores. b. Under what conditions are media typically sterilized in an autoclave? Media are sterilized at 121ºC with 15 psi of steam for at least 15 minutes. c. What type of media components cannot be sterilized in an autoclave? Heat-sensitive media additives cannot be sterilized by autoclaving d. What is an alternative to autoclaving for sterilizing heat sensitive materials? It is the filter sterilization can be used for liquid components that cannot be autoclaved. 6. Mannitol-salt agar (MSA) is a selective and differential medium. a. What is a selective medium? What component(s) of MSA make it selective? A selective medium enables one kind of microbe to grow while inhibiting another. MSA contains 7.5% NaCl, which, apart from staphylococci, inhibits the growth of most bacteria. 137

Culture Media Preparation

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b. What is a differential medium? What component(s) of MSA make it differential? A differential medium shows differences between two kinds of microbes that grow on the medium (usually color). MSA produces a pH indicator, phenol red, which, if acid is formed, changes from pink to yellow, indicating that mannitol fermentation has occurred. c. This medium is useful for the isolation and characterization of which microorganisms? MSA is beneficial for staphylococci isolation and S differentiation, from most other staphylococci aureus (mannito fermenter) (non-fermenters). 7. Agar is a solidifying agent used in media preparation. a. What is its origin? It is a complex polysaccharide isolated from seaweed b. What makes it ideal for cultivation of microbes? Agar melts at 100oC, but does not solidify until it reaches 45oC, and does not kill microbial cells, so molten media (e.g. pouring plates) can be inoculated. c. How and why does the agar concentration in semisolid media differ from conventional solid media? Solid media with a concentration of 1.5 percent, a semisolid medium has an agar concentration of 0.4 percent. For motility studies, Semisolid media can be used because they allow movement.

B. Multiple Choice

d. photoheterotrophs.

Select the answer that best completes the following questions.

1. Most bacteria derive their carbon and energy needs from organic molecules and are classified as a. chemolithotrophs. b. chemoorganotrophs. c. photoautotrophs. d. photoheterotrophs. 2. The cyanobacteria use solar energy to fix carbon dioxide. They are classified as a. chemolithotrophs. b. chemoorganotrophs. c. photoautotrophs. d. photoheterotrophs. 3. Rhizobium and Azotobacter are examples of nitrogen-fixing soil bacteria that are classified as a. chemolithotrophs. b. chemoorganotrophs. c. photoautotrophs. d. photoheterotrophs. 4. Some purple nonsulfur bacteria utilize solar energy but require an organic carbon source. They are classified as a. chemolithotrophs. b. chemoorganotrophs. c. photoautotrophs.

ANSWERS Multiple Choice

1. B. chemoorganotrophs 2. C. photoautotrophs 3. A. chemolithotrophs 4. D. photoheterotrophs...