Microbiology Labs I
- Page ID
- 3249
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- 1: Media Preparation
- Bacteria and fungi are grown on or in microbiological media of various types. The medium that is used to culture the microorganism depends on the microorganism that one is trying to isolate or identify. Different nutrients may be added to the medium, making it higher in protein or in sugar. Various pH indicators are often added for differentiation of microbes based on their biochemical reactions. Other added ingredients may be growth factors, NaCl, and pH buffers.
- 7: Isolation of an Antibiotic Producer from soil
- Soil is the major reservoir of microorganisms that produce antibiotics.Considering that soil is densely packed with microorganisms, it is not a wonder that many bacterial and fungal species have evolved over the eons to develop ways of inhibiting their neighbors for the benefit of their own growth. An antibiotic made by a microbe can inhibit many other soil microbes.
- 8: Bacterial Colony Morphology
- Bacteria grow on solid media as colonies. A colony is defined as a visible mass of microorganisms all originating from a single mother cell, therefore a colony constitutes a clone of bacteria all genetically alike.
- 9: Kirby-Bauer (Antibiotic Sensitivity)
- The Kirby-Bauer test for antibiotic susceptibility (also called the disc diffusion test) is a standard that has been used for years. It has been superseded by automated tests, but the K-B is still used in some labs, or used with certain bacteria that automation does not work well with. This test is used to determine the resistance or sensitivity of aerobes or facultative anaerobes to specific chemicals, which can then be used by the clinician for treatment of patients with bacterial infections.
- 10: Antimicrobial Chemicals
- Many herbs and spices MAY have (some documented, some just hearsay) antimicrobial activity: thyme, cinnamon, garlic, ginger, chamomile, oregano, sage, echinacea, wasabi, etc. We are going to try some out in this lab: fresh or dried, leaf or powder. In addition, you will be running various antimicrobial chemicals against your bacteria. To save on time, for the identification of antibacterial spices, each group will extract a different plant tissue and prepare enough herb/spice extract for each gr
- 11: Bacterial Numbers
- Many studies require the quantitative determination of bacterial populations. The two most widely used methods for determining bacterial numbers are the standard, or viable, plate count method and spectrophotometric (turbidimetric) analysis. Although the two methods are somewhat similar in the results they yield, there are distinct differences.
- 12: Oral Biofilms
- Most of the time in the microbiology lab, we study free-floating bacteria in broths or bacteria in colony forms, and generally in pure culture. However, in the real world bacteria are usually interacting with other species in pretty sophisticated ecosystems. This assemblage of various organisms attached to a surface is called a biofilm , and the organisms that comprise it can include bacteria, plants, fungi, protozoa, and even multicellular animals, depending on where the biofilm is.
- 14: Use of the Microscope
- The microscope is absolutely essential to the microbiology lab: most microorganisms cannot be seen without the aid of a microscope, save some fungi. And, of course, there are some microbes which cannot be seen even with a microscope, unless it is an electron microscope, such as the viruses.
- 17: Gram Stain
- The gram stain, originally developed in 1884 by Christian Gram, is probably the most important procedure in all of microbiology. It has to be one of the most repeated procedures done in any lab. Gram was actually using dyes on human cells, and found that bacteria preferentially bind some dyes. The Gram stain is a differential stain.
- 21: Capsule Stain
- The capsule is a thick polysaccharide layer around the outside of the cell. It is nonionic, so the dyes that we commonly use will not bind to it. Two dyes, one acidic and one basic, are used to stain the background and the cell wall, respectively. The area between the 2 dyes is the halo of the capsule surrounding the cell. The capsule gives added protection to the bacteria, making it virtually impossible to be phagocytosed by white blood cells.
- 26: Catalase Test
- Hydrogen peroxide H₂O₂ is a by-product of respiration and is lethal if it accumulates in the cell. The enzyme catalase degrades the hydrogen peroxide in the cell before it can do any cell damage. It splits the H₂O₂ to free oxygen (bubbles) and water. Generally, the test reaction is very fast and obvious bubbles will be seen. Catalase is made by your own cells, as well as a variety of other cells, including many bacteria. This test is particularly important for the gram+ bacteria.
- 49: Bacteriophages (Experiment)
- Bacteriophages are viruses which infect bacteria. In this lab, 2 kinds of bacteriophages will be used---T4 and phi 174 viruses. Their host bacteria are 2 different strains of E. coli,so these bacteriophages are called coliphages. The purpose of using 2 different viruses is to show the specificity of a virus for its host, even for these little bacterial viruses. The liquefied tryptone soft agar, into which the bacteria and viruses are placed, has less agar concentration than normal liquefied agar
- 53: Serology - Antigen-Antibody Tests
- Any feature that can elicit an immune response is called an antigen. The immune system makes proteins called immunoglobulins or antibodies which bind to an antigen to either directly neutralize the antigen or cause it to be cleared more efficiently by other components of the immune system. Antibodies linked to large particles such as latex beads can be used to agglutinate microorganisms using specific reactive antibodies.