Biochemical Tests

Biochemical tests are tests that help in the identification and differentiation of bacteria based on their metabolic activities. Each bacteria utilizes certain compounds (such as carbohydrate, protein, organic compounds) depending upon the availability of enzymes or appropriate environmental conditions (availability or lack of oxygen).

The end product of such reactions can be detected either by pH changes or by using indicator chemicals. The end results of such metabolic reactions form the basis of identification and differentiation of bacteria either to genus or up to species level.

API and RAPID ID For Microbial Identification

API and RAPID ID For Microbial Identification

BioMérieux's API identification products are test kits for the identification of Gram-positive bacteria, Gram-negative bacteria, and yeast.

Hydrogen Sulfide (H₂S) Production Test

Hydrogen Sulfide (H₂S) Production Test

Bacterial species capable of producing H₂S release sulfide which combines with iron present in the medium forming black precipitate.

Starch Hydrolysis Test: Principle, Procedure, Results

Starch Hydrolysis Test: Principle, Procedure, Results

Some bacteria such as Bacillus sps can hydrolyze starch (amylose and amylopectin) using the enzymes α-amylase and oligo-1,6-glucosidase.

Furazolidone Disk Test: Principle, Procedure Results

Furazolidone Disk Test: Principle, Procedure Results

Furazolidone disk test is used to differentiate staphylococci (sensitive) from micrococci (resistant).

Kligler’s Iron Agar (KIA): Principle, Procedure, Results

Kligler’s Iron Agar (KIA): Principle, Procedure, Results

Kligler Iron Agar is used for the differentiation of microorganisms on the basis of glucose and lactose fermentation and H₂S production.

Carbohydrate Fermentation Test: Uses, Principle, Procedure, Results

Carbohydrate Fermentation Test: Uses, Principle, Procedure, Results

It tests for the presence of acid and/or gas produced from carbohydrate fermentation. and is useful in differentiating among bacterial groups or species.

Robertson’s Cooked Meat (RCM) Medium

Robertson’s Cooked Meat (RCM) Medium

The most widely used anaerobic culture medium containing chopped meat particles and used for maintenance of stock cultures.

Phenylalanine Deaminase Test: Principle, Procedure, Results

Phenylalanine Deaminase Test: Principle, Procedure, Results

Some organism such as Proteus oxidatively deaminate phenylalanine to phenyl-pyruvic acid.

Oxidative fermentative (OF) test:  Principle, Procedure, Results

Oxidative fermentative (OF) test:  Principle, Procedure, Results

The oxidative-fermentative (OF) test is used to differentiate oxidative bacteria from fermentative bacteria based on acid production.

Elek Test: Principle, Procedure, Results

Elek Test: Principle, Procedure, Results

Elek test is an in vitro immunoprecipitation test to determine whether or not a strain of Corynebacterium diphtheriae is toxigenic.

Tests for Bacterial Motility: Procedure, Results

Tests for Bacterial Motility: Procedure, Results

These tests determine if an organism is motile (possesses flagella).

Nagler Reaction (Lecithinase Test)

Nagler Reaction (Lecithinase Test)

Lecithinase test is a biochemical test used to identify organisms that liberate phospholipases (lecithinases) e.g. Clostridium perfringens.

Acetate Utilization Test: Principle, Procedure, Uses

Acetate Utilization Test: Principle, Procedure, Uses

Acetate utilization test determines if an organism can use acetate as the sole source of carbon.

Butyrate Disk Test: Principle, Procedure, Results, Uses

Butyrate Disk Test: Principle, Procedure, Results, Uses

Rapid test for identifying Moraxella (Branhamella) catarrhalis which produce butyrate esterase enzyme.

Cetrimide Agar: Composition, Preparation, Uses

Cetrimide Agar: Composition, Preparation, Uses

Cetrimide agar test the ability of an organism to grow in the presence of cetrimide.

API 20E Test System: Results and Interpretations

API 20E Test System: Results and Interpretations

API-20E test strip (from bioMerieux, Inc.) is used to identify the enteric gram negative rods.

Nitrocefin test: Principle, Procedure, Uses

Nitrocefin test: Principle, Procedure, Uses

The nitrocefin test is a sensitive technique for detecting beta-lactamase-producing strains of N. gonorrhoeae, H. influenzae, Enterococcus spp.

Voges Proskauer (VP) Test: Principle, Procedure, Results

Voges Proskauer (VP) Test: Principle, Procedure, Results

Certain bacteria produce acetoin as the chief end product of glucose fermentation. Acetoin gets oxidized to diacetyl giving red color.

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Decarboxylation Test: Types, Principles, Uses

The presence of lysine, ornithine, and arginine decarboxylase enzyme is routinely tested in the identification of Enterobacteriaceae.

Hippurate Hydrolysis Test: Principle, Procedure, Results

Hippurate Hydrolysis Test: Principle, Procedure, Results

Campylobacter jejuni, Listeria monocytogenes, Gardnerella vaginalis, and Streptococcus agalactiae are positive for hippurate hydrolysis test.

Lancefield Classification of Streptococci

Lancefield Classification of Streptococci

Beta hemolytic streptococci are arranged into twenty (20) groups A-U without I and J (i.e. A through H and K through V).

Tween 80 Hydrolysis Test: Principle, Procedure, Results

Tween 80 Hydrolysis Test: Principle, Procedure, Results

Mycobacterium species possess an enzyme-lipase, that splits Tween-80 and releases oleic acid and polyoxyethylated sorbitol.

ONPG: β-galactosidase Test

ONPG: β-galactosidase Test

Organism producing β-galactosidase hydrolyzes the ONPG producing visible yellow product (orthonitrophenol).

Nitrate Reduction Test: Principle, Procedure, Results

Nitrate Reduction Test: Principle, Procedure, Results

Nitrate reduction test is used to determine the ability of an organism to reduce nitrate.

Culture media for Salmonella typhi and paratyphi

Culture media for Salmonella typhi and paratyphi

Common culture media are bismuth sulfite agar, MacConkey agar, deoxycholate citrate agar, xylose lysine deoxycholate agar, salmonella-shigella agar, etc.

String test for Lab diagnosis of Vibrio cholerae

String test for Lab diagnosis of Vibrio cholerae

V. cholerae emulsified in sodium deoxycholate, it lyses the cell wall and releases DNA giving a mucoid “string” when a loop is drawn away.

DNase Test: Principle, Procedure, Results

DNase Test: Principle, Procedure, Results

DNase test determines the ability of an organism to hydrolyze DNA.

Methyl Red (MR) Test: Principle, Procedure, and Results

Methyl Red (MR) Test: Principle, Procedure, and Results

Certain bacteria ferment glucose to produce stronger acids that take the media pH below 4.4 in which Methyl Red indicator turns red.

Gelatin Hydrolysis Test: Principle, Procedure, Results

Gelatin Hydrolysis Test: Principle, Procedure, Results

Gelatin hydrolysis test determines the ability of an organism to produce gelatinases that liquefy gelatin.

Bile-Esculin test for Enterococcus species

Bile-Esculin test for Enterococcus species

Bile-esculin test is widely used to differentiate Enterococci and Non-enterococcus group D streptococci from non-group D viridans group streptococci.

Salt Tolerance Test for Enterococcus species

Salt Tolerance Test for Enterococcus species

Salt tolerance test determines the ability of an organism to grow in high concentrations of salt (6.5%).

PYR Test: Principle, Procedure, Results

PYR Test: Principle, Procedure, Results

Some gram-positive cocci such as Enterococcus produces enzyme L-pyrroglutamylaminopeptidase that hydrolyze PYR substrate.

CAMP Test: Principle, Procedure, and Results

CAMP Test: Principle, Procedure, and Results

Group B Streptococci produce CAMP factor that acts synergistically with beta-lysin of S. aureus.

Catalase test: Principle, Procedure, Results, Uses

Catalase test: Principle, Procedure, Results, Uses

Catalase test is used to distinguish among Gram-positive cocci. Staphylococci are catalase-positive but Streptococci are catalase-negative.

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Weil Felix Test: Principle, Procedure, Limitation

Weil-Felix is a nonspecific agglutination test that detects anti-rickettsial antibodies in patient serum using OX strains of Proteus vulgaris.

Biochemical Tests to identify Mycobacteria, NTM

Biochemical Tests to identify Mycobacteria, NTM

Tests are; Tween-80 hydrolysis test, niacin test, nitrate reduction test, tellurite reduction test, urea hydrolysis test and citrate utilization test.

Novobiocin Susceptibility Test: Principle, Procedure, Results

Novobiocin Susceptibility Test: Principle, Procedure, Results

Novobiocin test is used to differentiate CONS and presumptively identify the isolate as Staphylococcus saprophyticus (novobiocin resistant).

IMViC Tests: Principle, Procedure, Results

IMViC Tests: Principle, Procedure, Results

IMViC is an acronym that stands for four different tests; indole test, methyl red test, Voges-Proskauer test, and citrate utilization test.

MUG  (Beta-Glucuronidase) Test for E. coli

MUG (Beta-Glucuronidase) Test for E. coli

Escherichia coli produces the enzyme beta-D-glucuronidase, which hydrolyzes a substrate giving blue fluorescence.

Triple Sugar Iron (TSI) Agar: Principle, Results, and Interpretation

Triple Sugar Iron (TSI) Agar: Principle, Results, and Interpretation

TSI test determines whether a gram-negative rod utilizes glucose, and lactose or sucrose fermentatively and forms hydrogen sulfide.

Optochin Sensitivity Test: Principle, Procedure, Results

Optochin Sensitivity Test: Principle, Procedure, Results

Optochin (ethylhydrocupreine hydrochloride) lyses pneumococci (positive) but alpha-streptococci are resistant (negative).

Bile Solubility Test: Principle, Procedure, Results

Bile Solubility Test: Principle, Procedure, Results

Bile solubility test differentiates S. pneumoniae (positive) from alpha-hemolytic streptococci (negative).

Citrate Utilization Test: Principle, Procedure, Results

Citrate Utilization Test: Principle, Procedure, Results

Citrate test determines the ability of an organism to utilize sodium citrate as source source of carbon.

Bacitracin Test: Principle, Procedure, Results

Bacitracin Test: Principle, Procedure, Results

Bacitracin test differentiates S. pyogenes (inhibited) from other beta-hemolytic streptococci.

Biochemical Tests for Bacterial Identification

Biochemical Tests for Bacterial Identification

Catalase test, oxidase test, MUG test, optochin sensitivity test, bacitracin sensitivity test, coagulase test, etc are some of the common biochemical tests.

Culture Media: PH Indicators, Color of Colonies

Culture Media: PH Indicators, Color of Colonies

Characteristics pigmentation observed in the culture media is because of the changes in the pH of the medium.

Urease Test: Principle, Procedure, Results

Urease Test: Principle, Procedure, Results

This test determines the ability of an organism to produce the enzyme urease which hydrolyzes urea.

Oxidase Test: Principle, Procedure, Results

Oxidase Test: Principle, Procedure, Results

Organism having cytochrome oxidase oxidizes tetramethyl-p-phenylenediamine hydrochloride to indophenol (a dark purple-colored) compound.

Coagulase Test: Principle, Procedure, Results

Coagulase Test: Principle, Procedure, Results

Coagulase test detects clumping factors and bound coagulase and differentiates Staphylococcus aureus (positive) from CoNS (negative).

Indole Test: Principle, Procedure, Results

Indole Test: Principle, Procedure, Results

Indole test determines the ability of an organism to split tryptophan to form indole.