Biochemical Test Archives - Microbiology Info.com

Litmus Milk Test – Principle, Procedure, Uses and Interpretation

Milk is an excellent medium for the growth of microorganisms because it contains the milk protein casein, the sugar lactose, vitamins, minerals and water. Litmus milk is a milk-based medium used to distinguish between different species of bacteria. The lactose (milk sugar), litmus (pH indicator), and casein (milk protein) contained within the medium can all be metabolized by different types of bacteria. The test …

Nitrate Reduction Test – Principle, 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 …

Hydrogen Sulfide Test – Principle, Procedure, Uses and Interpretation

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 …

Lysine Iron Agar (LIA) Slants Test – 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 …

Kligler’s Iron Agar 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 …

Hippurate Hydrolysis 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 …

Amino Acid Decarboxylase Test – Procedure, Uses and Interpretation

Amino acids are metabolized variably by gram negative aerobic and facultatively anaerobic bacteria as well as gram positive cocci. These amino acids are decarboxylated, hydrolysed or deaminated depending on the organism and the amino acid in question. In decarboxylation, the enzymes break the bond holding the carboxylic (-COOH) group to the rest of the amino …

Ames Test – Introduction, Principle, Procedure, Uses and Result Interpretation

Ames test it is a biological assay to assess the mutagenic potential of chemical compounds. It utilizes bacteria to test whether a given chemical can cause mutations in the DNA of the test organism. The test was developed by Bruce N. Ames in 1970s to determine if a chemical at hand is a mutagen. Objective To determine …

PYR Test- Principle, Uses, Procedure and Result Interpretation

PYR (Pyrrolidonyl Aminopeptidase) Test is used for the detection of pyrolidonyl arylamidase (also called pyrrolidonyl aminopeptidase) activity in Streptococcus pyogenes (group A strep), Enterococcus spp., some coagulase-negative staphylococci, and some Enterobacteriaceae. It is also known as PYR (L-pyrrolidonyl-β-naphthylamide) which serve as a substrate for the detection of pyrrolidonyl peptidase. Facklam, Thacker, Fox and Eriquez reported …

Bile Solubility Test- Principle, Reagents, Procedure and Result Interpretation

Bile Solubility Test is the test which differentiate Streptococcus pneumoniae (positive- soluble) from alpha-hemolytic streptococci (negative- insoluble). Streptococcus pneumoniae is bile soluble whereas all other alpha-hemolytic streptococci are bile resistant. Principle of Bile Solubility Test S. pneumoniae has an autolytic enzyme which can be demonstrated by allowing a broth culture to age in the incubator; …

Urease Test- Principle, Media, Procedure and Result

Urea Agar was developed by Christensen in 1946 for the differentiation of enteric bacilli. The urease test is used to determine the ability of an organism to split urea, through the production of the enzyme urease. Principle of Urease Test Urea is the product of decarboxylation of amino acids. Hydrolysis of urea produces ammonia and CO2. The formation …

Citrate Utilization Test- Principle, Media, Procedure and Result

Result Interpretation of Citrate Utilization Test

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 …

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

Result Interpretation of Voges–Proskauer (VP) Test

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 …

Methyl Red (MR) Test- Principle, Procedure and Result Interpretation

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 …

Indole Test- Principle, Reagents, Procedure, Result Interpretation and Limitations

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 …

Oxidase Test- Principle, Uses, Procedure, Types, Result Interpretation, Examples and Limitations

The oxidase test detects the presence of a cytochrome oxidase system that will catalyse the transport of electrons between electron donors in the bacteria and a redox dye- tetramethyl-p-phenylene-diamine. The dye is reduced to deep purple color. This test is used to assist in the identification of Pseudomonas, Neisseria, Alcaligens, Aeromonas, Campylobacter, Vibrio, Brucella and …

Catalase Test- Principle, Uses, Procedure, Result Interpretation with Precautions

Result Interpretation of Catalase Test and Examples

This test demonstrate the presence of catalase, an enzyme that catalyses the release of oxygen from hydrogen peroxide (H2O2). It is used to differentiate those bacteria that produces an enzyme catalase, such as staphylococci, from non-catalase producing bacteria such as streptococci. Normally 3% H2O2 is used for the routine culture while 15% H2O2 is used …

Coagulase Test- Principle, Procedure, Types, Interpretation and Examples

Introduction to Coagulase Test Coagulase test is used to differentiate Staphylococcus aureus (positive) which produce the enzyme coagulase, from S. epidermis and S. saprophyticus (negative) which do not produce coagulase. i.e Coagulase Negative Staphylococcus (CONS). Principle of Coagulase Test Coagulase is an enzyme-like protein and causes plasma to clot by converting fibrinogen to fibrin. Staphylococcus aureus produces two forms …