Biochemical tests are laboratory procedures used to detect the presence of specific enzymes, metabolic pathways, or end products in microorganisms. By observing how a microbe metabolizes substrates or reacts to reagents, these assays help identify and differentiate bacteria and fungi. The outcomes – such as changes in colour, gas production, or precipitates – reveal enzymatic activities and nutritional needs.
Explanation
Biochemical testing exploits metabolic differences among microorganisms to distinguish species and genera. Bacteria vary in the enzymes they produce and the substrates they can use; these differences can be uncovered by incubating cultures in media containing specific carbohydrates, proteins or other compounds and looking for characteristic reactions. For example, fermentative organisms acidify carbohydrate media, turning pH indicators yellow, while oxidative species do not. Tests may detect the breakdown of amino acids, the production of gas or hydrogen sulphide, or the ability to utilise citrate as a sole carbon source. Such assays have been the backbone of classical bacterial identification. They are simple and inexpensive, but some take days to weeks to complete because the organism must grow enough to show the reaction. In clinical laboratories, biochemical profiles complement microscopic observation and Gram staining, and the results are compared with established keys to arrive at a presumptive identification.
Common Tests and Applications
A wide variety of biochemical tests exist, each targeting a specific enzyme or metabolic function. Carbohydrate fermentation tests measure acid and gas production from sugars such as glucose, lactose and sucrose. The IMViC series—indole, methyl red, Voges–Proskauer and citrate utilisation—is used to differentiate members of the Enterobacteriaceae. Catalase testing detects the enzyme that decomposes hydrogen peroxide and helps distinguish Staphylococcus (catalase positive) from host. A pathogenic microbe has the ability to invade, damage or disrupt normal physiological functions.Factors(...)</div>" href="https://askmicrobiology.com/glossary/pathogenic/" target="_blank" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex='0' role='link'>pathogenic species found in humans and(...)</div>" href="https://askmicrobiology.com/glossary/streptococcus/" target="_blank" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex='0' role='link'>Streptococcus (catalase negative). The oxidation of a chromogenic reducing agent.<br/>ExplanationAerobic(...)</div>" href="https://askmicrobiology.com/glossary/oxidase-test/" target="_blank" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex='0' role='link'>oxidase test identifies bacteria that possess cytochrome c oxidase, such as Pseudomonas species. Urease assays detect the hydrolysis of urea, and coagulase tests confirm Staphylococcus aureus by its ability to clot plasma. Other tools include triple sugar iron slants to assess sugar fermentation and gas or hydrogen sulphide production, and gelatin or starch hydrolysis to determine protease and amylase activity. Beyond clinical diagnostics, biochemical tests monitor water and food quality, support teaching laboratories and act as a reference when molecular methods give ambiguous results.
Biochemical testing remains a cornerstone of microbiological practice. Although automated systems and DNA-based assays now provide rapid identification, the interpretation of metabolic reactions continues to inform our understanding of archaea, fungi, protozoa and viruses.<br/>ExplanationThe adjective "microbial” refers to anything associated with microscopic life(...)</div>" href="https://askmicrobiology.com/glossary/microbial/" target="_blank" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex='0' role='link'>microbial physiology and diversity. Using a combination of tests ensures accurate identification and guides effective treatment or control measures.
Related Terms: Bacteriology, protozoa; viruses and prions, although not truly(...)</div>" href="https://askmicrobiology.com/glossary/microorganism/" target="_blank" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex='0' role='link'>microorganism. By analysing which nutrients an organism can utilise, the enzymes it produces(...)</div>" href="https://askmicrobiology.com/glossary/biochemical-characterization/" target="_blank" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex='0' role='link'>Biochemical Characterization, culture medium is a nutrient solution or solid preparation that provides the environment and nutrients required for microorganisms or cells to grow.ExplanationCulture media supply essential(...)</div>" href="https://askmicrobiology.com/glossary/culture-medium/" target="_blank" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex='0' role='link'>Culture medium, Metabolic pathway, Microbial identification