Free eBook: Biochemical Tests for Identification of Medical Bacteria - Methods and Applications
Biochemical Tests for Identification of Medical Bacteria: A Comprehensive Guide
Biochemical tests are widely used in microbiology to identify and differentiate bacteria based on their metabolic and enzymatic activities. These tests are especially important for medical purposes, as they can help diagnose infections, select appropriate antibiotics, and monitor the effectiveness of treatment. In this article, we will provide a comprehensive guide on biochemical tests for identification of medical bacteria, covering the following topics:
What are biochemical tests and why are they important?
How to perform biochemical tests for medical bacteria?
How to interpret and report the results of biochemical tests?
How to access and download scientific articles on biochemical tests for free?
By the end of this article, you will have a better understanding of the principles, methods, and applications of biochemical tests for medical bacteria.
biochemical tests for identification of medical bacteria free download
What are biochemical tests and why are they important?
Definition and purpose of biochemical tests
Biochemical tests are laboratory procedures that measure the presence or activity of specific substances or enzymes in bacterial cells or cultures. These substances or enzymes are usually involved in various metabolic pathways or reactions that are characteristic of certain bacterial groups or species. For example, some bacteria can ferment sugars, produce gas, hydrolyze proteins, degrade fats, or produce pigments. By detecting these biochemical properties, microbiologists can identify and differentiate bacteria based on their phenotypic traits.
Biochemical tests are important for several reasons. First, they can help diagnose bacterial infections by confirming the presence or absence of certain pathogens in clinical samples. Second, they can help select appropriate antibiotics by determining the susceptibility or resistance of bacteria to different drugs. Third, they can help monitor the effectiveness of treatment by evaluating the changes in bacterial growth or metabolism over time.
Types and examples of biochemical tests
There are many types of biochemical tests for medical bacteria, each with its own principle, procedure, and interpretation. Some of the most common types are:
Carbohydrate fermentation tests: These tests measure the ability of bacteria to ferment carbohydrates (such as glucose, lactose, or sucrose) into acids, gases, or alcohols. The indicator used is usually a pH-sensitive dye (such as phenol red) that changes color depending on the acidity or alkalinity of the medium. The presence or absence of gas production can also be observed by using a Durham tube (a small inverted tube) inside the test tube. Examples of carbohydrate fermentation tests are glucose fermentation test, lactose fermentation test, sucrose fermentation test, etc.
Oxidase test: This test detects the presence of cytochrome c oxidase, an enzyme that transfers electrons from a donor (such as reduced cytochrome c) to an acceptor (such as oxygen) in the electron transport chain. The indicator used is usually a colorless compound (such as tetramethyl-p-phenylenediamine) that turns dark purple when oxidized by cytochrome c oxidase. Examples of bacteria that are oxidase-positive are Pseudomonas aeruginosa, Neisseria gonorrhoeae, Neisseria meningitidis, etc.
Catalase test: This test detects the presence of catalase, an enzyme that breaks down hydrogen peroxide into water and oxygen. The indicator used is hydrogen peroxide itself, which bubbles when in contact with catalase. Examples of bacteria that are catalase-positive are Staphylococcus aureus, Escherichia coli, Bacillus subtilis, etc.Here is the continuation of the article:
Indole test: This test detects the presence of indole, a compound that is produced by some bacteria when they break down the amino acid tryptophan. The indicator used is Kovac's reagent, which contains p-dimethylaminobenzaldehyde, a compound that reacts with indole to form a red-colored complex. Examples of bacteria that are indole-positive are Escherichia coli, Proteus vulgaris, Klebsiella pneumoniae, etc.
Methyl red and Voges-Proskauer tests: These tests measure the type of fermentation products that bacteria produce from glucose. The methyl red test detects the presence of mixed acids, while the Voges-Proskauer test detects the presence of acetoin and 2,3-butanediol. The indicators used are methyl red and Barritt's reagent, respectively. Examples of bacteria that are methyl red-positive and Voges-Proskauer-negative are Escherichia coli, Salmonella typhimurium, Shigella dysenteriae, etc. Examples of bacteria that are methyl red-negative and Voges-Proskauer-positive are Enterobacter aerogenes, Klebsiella pneumoniae, Serratia marcescens, etc.
Citrate utilization test: This test measures the ability of bacteria to use citrate as their sole carbon source. The medium used is Simmons citrate agar, which contains sodium citrate, ammonium salts, and bromothymol blue as a pH indicator. Bacteria that can utilize citrate produce alkaline products that turn the medium from green to blue. Examples of bacteria that are citrate-positive are Enterobacter aerogenes, Klebsiella pneumoniae, Citrobacter freundii, etc.
These are just some examples of biochemical tests for medical bacteria. There are many more tests available for different bacterial groups or species, such as coagulase test, urease test, nitrate reduction test, etc. A table summarizing some of the common biochemical tests and their results for some medically important bacteria is shown below:
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Bacteria
Carbohydrate fermentation
Oxidase
Catalase
Indole
Methyl red
Voges-Proskauer
Citrate
Escherichia coli
+ (glucose, lactose)
-
+
+
+
-
-
Pseudomonas aeruginosa
- (glucose)
+
+
-
-
-+Staphylococcus aureus+ (glucose)-+----Klebsiella pneumoniae+ (glucose, lactose)-+--++Bacillus subtilis+ (glucose)-+----</td </tr How to perform biochemical tests for medical bacteria?
General steps and principles of biochemical tests
The general steps and principles of biochemical tests for medical bacteria are as follows:
Prepare the bacterial culture: The first step is to obtain a pure culture of the bacterium t