Bacterial Identification

Chemical Assays, Radioisotopic Methods, and Microelectrodes

There are numerous tests and assays available that are utilized to aid in bacterial identification in a variety of settings.

Learning Objectives

Contrast the different tests that can be used in studies of microbes

Key Takeaways

Key Points

  • Chemical assays used for bacterial identification utilize various components of the microorganisms including structural, cellular and metabolic indicators.
  • Radioisotopic methods include the use of radioisotopes to help identify specific metabolic pathways utilized by bacteria by tracking uptake and breakdown of specific nutrients labeled with radioactivity.
  • Micro-electrodes are commonly being used in bacterial identification, specifically for pathogenic bacteria, as a means to identify biological components in a variety of environments by combining with bio-sensors.

Key Terms

  • peptidoglycan: A polymer of glycan and peptides found in bacterial cell walls.

Within the field of microbiology, there are specific tests or assays utilized to quantitatively and qualitatively measure microorganism components. These assays are often utilized to aid in bacterial identification. Three major types used for this purpose include chemical assays, radio isotopic methods and the use of micro electrodes. The following is an overview of these methodologies.

Chemical Assays

Chemical assays are utilized to identify and determine chemical components within a microorganism. Many of these assays test for specific cellular components and may have overlap with chemical analysis, which focuses on exact chemical composition.

Gram Staining

Examples of chemical assays include the classic test for Gram-positive or Gram-negative bacteria via Gram staining. Gram staining is utilized to differentiate bacteria into either of these Gram groups. The Gram staining technique is based on both chemical and physical properties of bacterial cell walls and tests for the presence of peptidoglycan.

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Gram Staining: An example of a chemical assay used for bacterial identification.

Oxidative-Fermentation Glucose Test

The O-F test is utilized to determine the way in which a bacteria is capable of metabolizing carbohydrates such as glucose. The two major mechanisms from which bacteria can obtain energy include oxidation of glucose and lactose fermentation. This specific assay identifies which method bacteria use by cultivating bacteria in various conditions.

Hydrolysis Tests

The process of hydrolysis is characterized by the ability to chemically split a molecule by the addition of water. There are numerous tests utilized in bacterial identification which involve testing for hydrolysis of specific substances. These tests include hydrolysis of starch, lipids, casein and gelatin. The basis of these tests is to identify and determine if a microbe has the proper enzymes and molecules to breakdown and use these specific molecules as sources of energy for cellular growth.

Radioisotopic Methods

Radioisotopes are specific types of isotopes that emit radioactivity. Isotopes of an element vary in the number of neutrons within their nuclei. In the field of microbiology, radioisotopes have been used

Micro-electrodes

Electrodes are characterized by a system of electrical conductors that are used to make contact with a non-metallic portion of a circuit. In regards to microbiology and bacterial identification, micro-electrodes are commonly being utilized to identify pathogenic bacteria in numerous settings. The micro-electrodes have the capability to function as bio-sensors and detect specific biological components of microbes.

Stable Isotopes

Stable isotopes are atoms that are not radioactive, in other words, they are not going to lose neutrons and decay spontaneously.

Learning Objectives

Demonstrate how isotopes are used in bacterial identification

Key Takeaways

Key Points

  • The term isotope refers to the number of neutrons a certain element contains.
  • Elements of the same name must always have the same number of protons, but the number of neutrons can change.
  • Adding or subtracting neutrons from an atom does not change the elemental properties, but it can alter some of its features (like making it more radioactive ).
  • While the number of neutrons in a particular atom can change, there is a certain threshold where the atom is given more neutrons that its nuclear force can hold. At this point, the atom is deemed unstable.
  • The atom will continue to lose neutrons, or decay, until it become stable again. A stable isotope is a chemical isotope that is not radioactive.

Key Terms

  • isotope: Any of two or more forms of an element where the atoms have the same number of protons, but a different number of neutrons within their nuclei. As a consequence, atoms for the same isotope will have the same atomic number but a different mass number (atomic weight).
  • atom: The smallest possible amount of matter which still retains its identity as a chemical element, now known to consist of a nucleus surrounded by electrons.
  • Radioactive: A particle that has spontaneous emission of ionizing radiation as a consequence of a nuclear reaction, or directly from the breakdown of an unstable nucleus.

Isotopes

The term isotope refers to the number of neutrons a certain element contains. Elements of the same name (for example, oxygen) must always have the same number of protons, but the number of neutrons can change. Adding or subtracting neutrons from an atom does not change the elemental properties, but it can alter some of its features (like making it more radioactive).

Stable Isotopes

While the number of neutrons in a particular atom can change, there is a certain threshold where the atom is given more neutrons that its nuclear force can hold. At this point, the neutrons start to be released. The release is also known as decay. During this time, the atom is deemed “unstable. ” The atom will continue to lose neutrons until it become stable again. A stable isotope is a chemical isotope that is not radioactive. There are some cases where atoms have no stable isotopes so they continue to lose neutrons, and later protons and electrons, until they become another element entirely. Research has shown that there are 80 elements with one or more stable isotopes. Of these, 26 have only one stable isotope which is also known as being monoisotopic. The element with the most stable isotopes is tin which as 10 stable isotopes.

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Table of Isotopes: This is a table that represents atom decay yielding various isotopes.

Extensions

Knowledge about stable isotopes is important in a variety of fields. Scientists have used information on these topics in botanical and plant biological investigations as well as ecological and biological studies. Additionally, some scientists have used oxygen isotope ratios to reconstruct historical atmospheric temperatures. This work is especially important due to our current concern with climate change/global warming.