Microorganisms exhibit diverse metabolic capabilities, and their ability to break down substrates varies significantly. This variation leads to different metabolic byproducts, which can be analyzed using biochemical methods for bacterial identification. Understanding the principles and applications of various biochemical reactions is essential for accurate bacterial classification. These physiological and biochemical traits are typically determined through tests outlined in the Shirling & Gottlieb International Journal of Systematic Bacteriology. (1) Carbohydrate Metabolism Experiment Sugar (Alcohol, Glycoside) Fermentation Test (1) Principle: Bacteria's ability to ferment sugars depends on the presence of specific enzymes that catalyze the breakdown of those sugars. The end products vary depending on the type of sugar and the bacteria involved. A pH indicator is often added to the medium to detect acid production. If acid is produced, the color of the medium changes, indicating fermentation. (2) Basic Medium: A variety of carbohydrates such as monosaccharides, disaccharides, polysaccharides, alcohols (e.g., mannitol, inositol), and glycosides (e.g., salicin, inulin) are added at concentrations ranging from 0.5% to 1%. The medium can be liquid, semi-solid, solid, or in microbiochemical tubes. (3) Experimental Method: A pure culture of the bacteria is inoculated into a medium containing glucose, lactose, maltose, mannitol, or sucrose and incubated at 37°C for 24 hours. Results are then observed and recorded. (4) Result Interpretation: If the bacteria ferment the sugar, the medium turns yellow due to acid production. If no fermentation occurs, the medium remains purple. In cases where gas is produced, bubbles may appear at the top of the tube. (5) Application: This test is fundamental in identifying Enterobacteriaceae species and is widely used in microbial diagnostics. Oxidation-Fermentation (O/F) Test (1) Principle: Bacteria can either oxidize glucose aerobically, ferment it anaerobically, or not decompose it at all. This distinction helps differentiate between different bacterial groups, such as micrococci and staphylococci, and members of the Enterobacteriaceae family. (2) Medium Composition: The medium contains peptone, sodium chloride, dipotassium phosphate, glucose, agar, and bromothymol blue. It is prepared and sterilized before use. (3) Experimental Procedure: Young cultures are inoculated into two tubes—one covered with paraffin oil and one not. After incubation at 37°C for 24 hours, results are evaluated based on color changes. (4) Result Interpretation: Positive results show color change, while negative results remain unchanged. This test is particularly useful for differentiating between aerobic and anaerobic bacteria. β-Galactosidase (ONPG) Test (1) Principle: Some bacteria produce β-galactosidase, which cleaves o-nitrophenyl-β-D-galactoside to form yellow o-nitrophenol. This reaction can be detected even at low concentrations. (2) Medium Preparation: The medium contains ONPG, phosphate buffer, and peptone water. It is filtered and sterilized before use. (3) Experimental Procedure: Bacterial cultures are inoculated into ONPG medium and incubated at 37°C for 1–3 hours or 24 hours. A yellow color indicates a positive result. (4) Application: This test is commonly used for identifying Gram-negative bacteria and certain enteric organisms. Esculin Hydrolysis Test (1) Principle: Some bacteria hydrolyze esculin to esculetin and glucose. Esculetin reacts with iron ions in the medium to form a black compound, resulting in a darkened medium. (2) Application: This test is used to identify species like Enterococcus and Streptococcus, with positive results for Enterococcus and negative for most Streptococcus species. Methyl Red Test (1) Principle: When bacteria ferment glucose and produce significant acid, the pH drops below 4.5, causing methyl red to turn red. If less acid is produced or further metabolized, the pH remains above 6.2, and the indicator remains yellow. (2) Experimental Method: Bacterial cultures are inoculated into glucose broth and incubated for 48–72 hours. Methyl red reagent is then added, and the color change is observed. (3) Application: This test is frequently used to distinguish Escherichia coli (positive) from Enterobacter aerogenes (negative). Voges-Proskauer (VP) Test (1) Principle: Some bacteria convert glucose to pyruvic acid, which is then decarboxylated to acetyl methyl carbinol. In an alkaline environment, this compound reacts with creatine to form a red compound. (2) Reagents: 40% NaOH and 0.3% creatine are used in the test. (3) Experimental Procedure: Cultures are incubated for 2–6 days, and the reagent is added. A red color within 10 minutes indicates a positive result. (4) Application: This test is often used alongside the methyl red test for bacterial differentiation. Protein and Amino Acid Metabolism Experiments Gelatin Liquefaction Test (1) Principle: Bacteria producing gelatinase can break down gelatin into amino acids, liquefying the medium. (2) Experimental Method: Isolated colonies are inoculated into gelatin medium and incubated at 30°C for 20 days. The medium is cooled to observe liquefaction. Indole Test (1) Principle: Bacteria containing tryptophanase can convert tryptophan into indole, which reacts with p-dimethylaminobenzaldehyde to form a red compound. (2) Medium: Peptone water is used as the base medium. (3) Experimental Method: Bacterial cultures are incubated in tryptophan-rich medium, and the reagent is added along the tube wall. A red color indicates a positive result. Hydrogen Sulfide Test (1) Principle: Bacteria breaking down sulfur-containing amino acids produce hydrogen sulfide, which forms a black precipitate when reacting with ferrous or lead ions. (2) Experimental Method: Bacteria are inoculated into lead acetate medium and incubated at 35°C for 24–48 hours. Black precipitates indicate a positive result. Urease Test (1) Principle: Bacteria producing urease break down urea into ammonia, making the medium alkaline. (2) Medium: Urea agar is used for this test. Phenylalanine Deaminase Test (1) Principle: Some bacteria deaminate phenylalanine to form phenylpyruvate, which reacts with ferric chloride to produce a green color. Amino Acid Decarboxylase Test (1) Principle: Bacteria producing decarboxylase can break down amino acids, forming amines and CO₂, which alkalinizes the medium. Carbon and Nitrogen Source Utilization Tests Unique Carbon Source Utilization Test (1) Principle: Bacteria are tested for their ability to grow on a medium containing only one carbon source. Growth indicates utilization of that carbon source. Unique Nitrogen Source Utilization Test (1) Principle: Similar to the carbon source test, this evaluates whether bacteria can utilize a single nitrogen source as their sole nitrogen supply. Enzyme Activity Tests Oxidase Test (1) Principle: The oxidase enzyme catalyzes the oxidation of cytochrome C, which then oxidizes p-phenylenediamine to form a colored quinone compound. Catalase Test (1) Principle: Bacteria with catalase break down hydrogen peroxide into water and oxygen, producing visible bubbles. Nitrate Reduction Test (1) Principle: Bacteria reduce nitrate to nitrite or other compounds, which can be detected using reagents like sulfanilamide and N-(1-naphthyl)ethylenediamine. Amylase Test (1) Principle: Some bacteria secrete amylase, which breaks down starch into maltose and glucose. Iodine is used to detect unhydrolyzed starch, which turns blue, while hydrolyzed areas remain clear. Company Name: Qingdao Weisi Biotechnology Co., Ltd. Address: No. 17 Shanghai Road, Qingdao Economic and Technological Development Zone
Galvanized cable tray comes in various sizes and shapes, including straight sections, elbows, tees, crosses, and reducers. It is designed to be easy to install and maintain, and can be used in a variety of environments, including indoor and outdoor settings. Galvanized cable tray is commonly used in power plants, chemical plants, oil refineries, and other industrial facilities where there is a need for a reliable and robust cable management system.
Galvanized Cable Tray,Galvanized Steel Cable Tray,Galvanized Cable Trays,Galvanized Cable Ladder Rayhot Technology Group Co.,Ltd , https://www.cnrayhot.com
One of the benefits of galvanized cable tray is its resistance to corrosion. The zinc coating on the steel provides a protective layer that prevents rust and corrosion from forming on the surface of the tray. This makes galvanized cable tray ideal for use in environments where there is exposure to moisture, chemicals, and other corrosive substances.
Another advantage of galvanized cable tray is its strength. The steel used in galvanized cable tray is strong and durable, which means it can support heavy loads without bending or breaking. This makes it a popular choice for applications where there is a need for a sturdy and reliable cable management system.
Galvanized cable tray is also easy to install and maintain. The tray can be cut to size and shaped to fit around obstacles, making it a flexible solution for cable management. It can also be easily cleaned and maintained, which helps to extend its lifespan and keep it in good condition.
