Aseptic Technique & Culturing Microbes

A. What is the difference between a bactericidal and bacteriostatic agent? Between sterilization and disinfecting? Bactericidal agent refers to substances used to kill bacteria while bacteriostatic agent refers to substances used to restrict or to inhibit bacteria cells growth. Sterilization is the complete destruction or elimination of all viable organisms in or on an object while disinfection is the destruction of pathogenic nonsporulating microbes or their toxins usually on inanimate surfaces.

B. List five sterilization methods, how they work, and what they are used for.

Autoclaving (steam under pressure or pressure cooker) at 121oC for 15 minutes (15lbs/in2 pressure) is good for sterilizing almost anything; however, autoclaving will denature or destroy heat-labile substances. Dry heat (hot air oven) at 160oC for 2 hours or 170oC for 1 hour is used for glassware, metal, and objects that will not melt. Incineration burns organisms and physically destroys them. This method is used for needles, inoculating wires, glassware, etc. Boiling at 100oC for 30 minutes kills almost all endospores. Very long or intermittent boiling is required to kill endospores and sterilize a solution.

Toxic chemicals and gas such as formaldehyde, glutaraldehyde, and ethylene oxide can kill allforms of life in a specialized gas chamber. C. What is 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 can be correctly identified for accurate studying and testing, and diagnosis in a clinical environment for testing/experimenting with a pure culture ensures that the same results can be achieved regardless of how many times the test is repeated.

D. What is aseptic technique? Why is it so critical? Aseptic technique is a method of preventing unwanted microorganisms from gaining access to growth medium or culture. It allows the transfer of inoculum to a sterile medium without introducing any unwanted outside contaminants.

E. Describe three common forms of growth that you are likely to see in a broth culture?

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. Turbidity: The organisms appear as a general cloudiness throughout the broth. Sediment: A mass of organisms appears as a deposit at the bottom of the tube. F. What is the difference between an aerobic and an anaerobic bacterium? Aerobic bacteria are organisms that grow only in the presence of oxygen. They obtain energy from aerobic respiration while anaerobic are bacterium are microorganisms that grow best , or exclusively, in the absence of oxygen G. Describe the difference between facultative and obligate? Facultative are organisms that grow with or without oxygen but generally better with oxygen.

They obtain energy from aerobic respiration; anaerobic respiration and fermentation while on the other hand obligate are organisms that grow only without oxygen. Oxygen will inhibit or kill them. They obtain their energy from aerobic respiration or fermentation. H. Which two types of media did you use in this lab? Why did you need two types of media?

I. Using microscopic images of L. acidopholis and S. epidermidis in your textbook, lab manual or online, describe what L. acidopholis and S. epidermidis looks like. (shape, individual organisms or clumped groups, shape of clusters, etc.) arranged in grape-like clusters. L. acidopholis are usually straight, although it can form coccobacillary,which forms under certain conditions. They are often found in chains of varying length. S. epidermidis forms white, raised, cohesive colonies about 1–2 mm in diameter negative, facultative anaerobe that can grow by aerobic respiration or by fermentation. Some strains may not ferment J. Define the following terms:

Psychrophiles are cold-loving bacteria. Their optimum growth temperature is between -5°C and 15°C. They are usually found in the Arctic and Antarctic regions and in streams fed by glaciers. Mesophiles are bacteria that grow best at moderate temperatures. Their optimum growth temperature is between 25°C and 45°C. Most bacteria are mesophilic and include common soil bacteria and bacteria that live in and on the body. Thermophiles are heat-loving bacteria. Their optimum growth temperature is between 45°C and 70°C. They are commonly found in hot springs and compost heaps. Hyperthermophiles are bacteria that grow at very high temperatures. Their optimum growth temperature is between 70°C and 110°C. They are usually members of the Archaea and are found growing near hydrothermal vents at great depths in the ocean.

A. Which type of organisms did you use in this lab? (Thermophiles, mesophiles, psychophiles). We used two organisms S epidermidis and L. acidopholis both are mesophiles