Name and Course Section: Avital Gershtein, Section 701 Title: Aseptic Technique & culturing Microbes - Lab # 4 Purpose: The purpose of this experiment is to Learn and employ aseptic technique, to become familiar with basic requirements of microbial growth, to learn the basic forms of culture media, and to become familiar with methods used to control microbial growth. Bacteria
Growth pattern after 24 hours
Growth pattern after 48 hours
in liquid MRS broth
Amount of sediment grew over the marked line
in liquid nutrient broth
Procedure: After setting up the incubator, I aseptically transferred S. epidermidis and L. acidophilus. to generate liquid broth cultures. After waiting for 24-48 to observe growth, I recorded my observations. Then, I prepared wet mount slides and direct staining slides of both S. epidermidis and L. acidophilus. to observe them microscopically using oil immersion lens. When I was done, I stored them in the refrigerator for future use.
Observations/ Data Tables:
L. acidophilus (wet mount)
L. acidophilus (direct stain)
Large blue/purple round cells
S. epidermidis (wet mount)
Very small dots
S. epidermidis (direct stain)
Dots clumped into one group
Results/Analysis: Gained knowledge about culture media and how to distinguish various types of microbial growth. I also learn about variable conditions that are required for microbial growth, including oxygen levels and temperature.
A. What is the difference between a bactericidal and bacteriostatic agent? What is the difference between sterilization and disinfection?
Bactericidal refers to killing bacteria and bacteriostatic inhibits the growth of bacterial cells. Sterilization completes destruction of all microorganisms including spores and disinfecting kills microorganisms through chemical agent. B. List five microbial killing methods, how they work, and what they are used for.
Dry heat: Dry heat is used for materials that must remain dry and which are not destroyed at temperatures between 121oC and 170oC. The method is good for glassware and metal, but not plastic or rubber items.
Autoclave: Autoclaving kills all forms of life including bacterial endospores. The item being sterilized must be maintained at the effective temperature for the full time. Filtration: involves the physical exclusion and removal of all cells in a liquid or gas, and is especially important to sterilize solutions which would be denatured by heat Boiling: at 100oC for 30 minutes kills almost all endospores. Very long or intermittent boiling is required to kill endospores and sterilize a solution.
Incineration: burns organisms and physically destroys them. This method is used for needles, inoculating wires, glassware, etc.
C. What is a pure culture? Why is it important to work with a pure culture?
A pure culture is one in which all the organisms are descendants of the same organism. A pure culture ensures that only one type of bacteria is present and ensures one answer regardless of how many times you test it.
D. What is aseptic technique? Why is it so critical?
Aseptic technique is a method of preventing unwanted microorganisms and minimizing pathogens. It is important because it sterilizes the area.
E. Describe three common forms of growth that you are likely to see in a broth culture.
1. Pellicle: A mass of organisms floats in or on top of the broth. Smaller masses or clumps of organisms that are dispersed throughout the broth form an even pattern called flocculent. 2. Turbidity: The organisms appear as a general cloudiness throughout the broth.
3. Sediment: A mass of organisms appears as a deposit at the bottom of the tube.
F. What is the difference between an aerobe and an anaerobe?
Aerobe only grows in the presence of oxygen and anaerobe grows...
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