Biochemical Test

Deoxyribonucleic acid (DNA) is a large polymer of nucleotides that is way too large to enter the cell membrane. In order to utilize external DNA, bacteria cells secrete exoenzymes (DNases) outside of the cell that hydrolyze DNA into nucleotides.  The nucleotides can then move across the cell membrane via transport proteins to be utilized. The cell can …

Read moreDeoxyribonuclease (DNase) Test – Principle, Procedure, Uses and Interpretation

Cetrimide is a quaternary ammonium salt, which acts as a selective agent and inhibits most bacteria by acting as a cationic detergent (Cetyltrimethylammonium bromide). Cetrimide when added into a culture medium results into a selective solid medium recommended for use in qualitative procedures for selective isolation and presumptive identification of Pseudomonas aeruginosa and other nonfermentative, …

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Casein, the major milk protein, is a macromolecule composed of amino acid subunits linked together by peptide bonds (CO—NH). It makes around 85% of the protein found in milk as well as the white color of milk.  Casein is way too large to enter the cell membrane. Before their assimilation into the cell, proteins must …

Read moreCasein Hydrolysis Test – Principle, Procedure, Uses and Interpretation

Esculin is a glycosidic coumarin derivative (6-beta-glucoside-7-hydroxy-coumarin). The two moieties of the molecule (glucose and 7-hydroxycoumarin) are linked together by an ester bond through oxygen. Many bacteria can hydrolyze esculin, but few can do so in the presence of bile. Thus the bile esculin test is based on the ability of certain bacteria, notably the group …

Read moreBile Esculin Test – Principle, Procedure, Uses and Interpretation

Butyrate discs are employed in the microbiology lab for demonstrating the enzymatic hydrolysis of bromo-chloro-indolyl butyrate. The Test Disc is used for rapid detection and qualitative procedures of butyrate esterase for presumptive identification of Moraxella catarrhalis. Moraxella catarrhalis is recognized as a significant pathogen whose isolation from routine sputum cultures is associated with clinical infection. The …

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Different bacteria produce an important class of enzymes called beta-lactamases, which may be mediated by genes on plasmids or chromosomes. These enzymes confer resistance to a number of penicillin antibiotics by cleaving the beta-lactam ring of penicillins and cephalosporin antibiotics, resulting in inactivation of these drugs. They are capable of inactivating “penicillinase-labile-penicillins”, such as amoxicillin, …

Read moreBeta Lactamase Test – Principle, Procedure, Uses and Interpretation

Bacitracin is a polypeptide antibiotic produced by organisms of the licheniformis group of Bacillus subtilis var Tracy. It is used to determine its effect of a small amount (0.04 IU or 0.05 IU not higher) on different microorganisms. The presumptive identification of beta hemolytic Group A streptococci from beta hemolytic non-Group A Streptococci is usually done by testing for sensitivity …

Read moreBacitracin Susceptibility Test – Principle, Procedure, Uses and Interpretation

Acetamide test is used to test an organism’s ability to utilize acetamide by deamidation. It is used in the qualitative procedures to differentiate non-fermentative, gram negative bacteria, especially Pseudomonas aeruginosa, on the basis of acetamide utilization. Objective To differentiate microorganisms based on the ability to use acetamide as the sole source of carbon. Principle The …

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API identification products are test kits for identification of Gram positive and Gram negative bacteria and yeast. API strips give accurate identifications based on extensive databases and are standardized, easy-to-use test systems. The kits include strips that contain up to 20 miniature biochemical tests which are all quick, safe and easy to perform. API (Analytical …

Read moreAPI (Analytical Profile Index) 20E Test – Procedure, Uses and Interpretation

Anaerobic metabolism requires an electron acceptor other than atmospheric oxygen (O2). Many gram-negative bacteria use nitrate as the final electron acceptor. Nitrate reduction test is a test that determines the production of an enzyme called nitrate reductase, which results in the reduction of nitrate (NO3). Bacterial species may be differentiated on the basis of their …

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Some microorganisms have an ability to reduce sulfur (Sulphur) containing compounds to hydrogen sulfide during metabolism which is commonly employed as a test measure for their identification in laboratories. Numerous methods are used to detect H2S production by micro-organisms which vary with the source of sulfur and the metal salts used to indicate H2S formation. SIM …

Read moreHydrogen Sulfide Test – Principle, Procedure, Uses and Interpretation

Lysine iron agar (LIA) slants tests organisms for the ability to deaminate lysine or decarboxylate lysine. Lysine deamination is an aerobic process which occurs on the slant of the media. Lysine decarboxylation is an anaerobic process which occurs in the butt of the media. Principle Lysine iron agar contains lysine, peptones, a small amount of glucose, ferric ammonium citrate, and sodium thiosulfate. The medium has an aerobic …

Read moreLysine Iron Agar (LIA) Slants Test – Procedure, Uses and Interpretation

The Kligler’s Iron Agar test employs a medium for the identification of Enterobacteriaceae, based on double sugar fermentation and hydrogen sulphide production. In 1918, Kligler described a medium for detection of H2S and differentiation of Salmonella spp. Bailey and Lacey further modified the medium by substituting phenol red indicator for Andrade indicator. This medium became …

Read moreKligler’s Iron Agar Test – Procedure, Uses and Interpretation

Hippurate hydrolysis test is used to detect the ability of bacteria to hydrolyse substrate hippurate into glycine and benzoic acid by action of hippuricase enzyme present in bacteria. Hippuricase is a constitutive enzyme that hydrolyzes the substrate hippurate to produce the amino acid glycine. Glycine is detected by oxidation with Ninhydrin reagent, which results in …

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This test is among a suite of IMViC Tests (Indole, Methyl-Red, Vogues-Proskauer, and Citrate) that are used to differentiate among the Gram-Negative bacilli in the family Enterobacteriaceae. Principle of Citrate Utilization Test Citrate agar is used to test an organism’s ability to utilize citrate as a source of energy. The medium contains citrate as the sole carbon source and …

Read moreCitrate Utilization Test- Principle, Media, Procedure and Result

Voges and Proskauer, in 1898, first observed the production of a red color after the addition of potassium hydroxide to cultures grown on specific media. Harden later revealed that the development of the red color was a result of acetyl-methyl carbinol production. In 1936 Barrit made the test more sensitive by adding alpha-naphthol to the …

Read moreVoges–Proskauer (VP) Test- Principle, Reagents, Procedure and Result

The methyl red (MR) test detects the production of sufficient acid during the fermentation of glucose and the maintenance of conditions such that the pH of an old culture is sustained below a value of about 4.5, as shown by a change in the colour of the methyl red indicator which is added at the …

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This test demonstrate the ability of certain bacteria to decompose the amino acid tryptophane to indole, which accumulates in the medium. Indole production test is important in the identification of Enterobacteria. Most strains of E. coli, P. vulgaris, P. rettgeri, M. morgani and Providencia species break down the amino acid tryptophan with the release of indole. This is performed …

Read moreIndole Test- Principle, Reagents, Procedure, Result Interpretation and Limitations