Category archives for Tests for identification of bacteria

X and V factor test: Identification test for Haemophilus

Members of the genus Haemophilus are fastidious in nature. i.e. they require extra nutritional supplements in order to grow.  Some Hemophilus require only X factor (haemin-which is present on blood agar)  or only V factor (Nicotinamide-adenine dinucleotide, NAD- which is present within the blood cells) or a combination of both. So,  Haemophilus influenzae grows only […]

Oxidation Fermentation (OF) test: Principle, Procedure and Result Interpretation

Oxidation Fermentation (OF) test is used to differentiate those organisms that utilize carbohydrates aerobically (Oxidation) such as Pseudomonas aeruginosa, from those that utilize carbohydrates anaerobically (Fermentation) such as members of the Enterobacteriaaceae and those that do not utilize carbohydrates at all (Non fermenters) such as Alcaligenes faecalis  . This test was developed by Hugh and […]

Tween 80 hydrolysis test

Tween 80 hydrolysis test is used mainly to differentiate slow–growing Mycobacterium (Scotochromogens) with similar colony appearance, M. gordonae (positive) and M. scrofulaceum (negative). This test is also useful in identifying M. kansasii (positive results within 24 hours). Those Mycobacterium spp that produce lipase hydrolyse the detergent Tween 80 (polyethylene derivative of sorbitan mono-oleate) with the production of oleic acid and polyoxyethylated […]

Hanging drop test/preparation

Hanging drop test is a confirmatory test to identify if an organism is motile or non motile. It can also be used for the presumptive identification of organism on the basis of its characteristic motility like Vibrio cholerae which has a darting type of motility in stool sample of patients with cholera. This test is prepared […]

Hydrogen sulphide (H2S) production test

Hydrogen sulphide (H2S) production test is used for the detection of hydrogen sulphide (H2S) gas produced by an organism. It is used mainly to assist in the identification of members of family Enterobacteriaceae and occasionally to differentiate other bacteria such as Bacteroides sps and Brucella sps. H2S is produced when sulphur – containing amino acids […]

Voges Proskauer test (VP test): Principle, Procedure, Interpretation and Quality Control

Voges-Proskauer test is one of the tests used for identification of Enterobacteriaceae. It is usually performed alongside the methyl red test since both tests are performed on cultures grown in MR-VP broth.  Both tests are based on the detection of end products from the metabolism of glucose. VP test is based on the detection of […]

Oxidative/Fermentative Test (O/F test)

Oxidative/Fermentative (O/F) test is done to distinguish between aerobes and anaerobes through their ability to breakdown carbohydrates. In this test, a semi solid medium containing a carbohydrate (usually glucose) and a pH indicator is used.  If acid is produced only at the surface of the medium, where conditions are aerobic, the attack on sugar is […]

Novobiocin susceptibility test

The speciation of coagulase negative Staphylococcus is necessary in certain culture specimens. Coagulase negative staphylococci can either be resistant or susceptible to novobiocin. The one most commonly isolated novobiocin resistant coagulase negative staphylococcus from urine is Staphylococcus saprophyticus. It is one of the most common causes of urinary tract infections in sexually active young women. So, […]

Bile solubility test: Principle, Procedure and Expected results

Principle of Bile Solubility test: Bile solubility test is used to differentiate Streptococcus pneumoniae from other alpha-hemolytic Streptococci. Streptococcus pneumoniae is bile soluble whereas all other alpha-hemolytic streptococci are insoluble. Bile or a solution of bile salt, like sodium desoxycholate rapidly lyses the pneumococcal colonies. This lysis depends on the presence of intracellular autolytic enzyme. Bile […]

CAMP test and Reverse CAMP test

CAMP (Christie, Atkins, and Munch-Peterson) test is used for the presumptive identification of Group B Streptococcus (Streptococcus agalactiae). It is the only beta-hemolytic Streptococcus which yields a positive CAMP test. The test has been named after Christie, Atkins, and Munch-Peterson, who described it in 1944.  a Principle of CAMP test CAMP test is done to detect […]

Leucine amino peptidase (LAP) test for identification of catalase negative gram positive cocci

Principle of  Leucine amino peptidase (LAP) test: Leucine amino peptidase (LAP) test is used for the preliminary characterization of catalase negative, gram-positive  cocci.  This is a rapid test for detection of enzyme leucine aminopeptidase. Leucine- β- napthalamide impregnated disk serves as a substrate for the detection of leucine aminopeptidas.  This enzyme hydrolyse the substrate resulting […]

Gelatin hydrolysis test: Principle, Procedure, Interpretation and preparation of nutrient gelatin medium

Gelatin hydrolysis is helpful in identifying and differentiating species of Bacillus, Clostridium, Proteus, Pseudomonas, and Serratia.  It also distinguishes the gelatinase-positive, pathogenic Staphylococcus aureus from the gelatinase-negative, non-pathogenic S. epidermidis . Gram-positive, spore-forming, rodshaped, aerobic or anaerobic bacteria such as Bacillus anthracis, Bacillus cereus, Bacillus subtilis, Clostridium perfringens and Clostridium tetani, are also positive for […]

Hippurate hydrolysis test

Hippurate hydrolysis test can be used for presumptive identification of Gardnerella vaginalis, Campylobacter jejuni, Listeria monocytogenes and group B streptococci. Principle of Hippurate hydrolysis test Hippurate hydrolysis test is used to detect the ability of bacteria to hydrolyse hippurate into glycine and benzoic acid by action of hippuricase enzyme present in bacteria. Previously, it was tested using ferric chloride […]

Urea hydrolysis/ Urease test (Christensen’s method)

Urea hydrolysis/Urease test is used to detect the ability of an organism to produce urease that hydrolyses urea contained in the medium. Hydrolysis of urea produces ammonia and carbon dioxide  The formation of ammonia makes the medium alkaline and the shift in pH is detected by the change of color of indicator phenol red from light […]

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

Principle: Triple sugar iron agar test is used to determine whether gram negative bacilli utilize glucose and lactose or sucrose fermentatively and produce hydrogen sulfide (H2S).  It contains 10 parts of lactose: 10 parts of sucrose: 1 part of glucose and peptone.  Phenol red and ferrous sulphate serves as an indicator for acidification of medium […]

Citrate utilisation test: Principle, Procedure and Expected results

Principle Citrate utilisation test is used to detect the ability of an organism to utilize sodium citratre as a sole source of carbon and ammonium salt as a sole source of nitrogen. Bacteria that grow in the medium turn the medium alkaline. This is indicated by the change of color of bromothymol blue indicator from […]

Coagulase test: Principle, Procedure and Interpretation

Coagulase test is done to distinguish Staphylococcus aureus from other Coagulase negative Staphylococci (CONS) like Staphylococcus epidermidis, Staphylococcus saprophyticus etc. Staphylococcus  aureus produces two types of coagulase, i.e. free coagulase and bound coagulase. Free coagulase is an extracellular enzyme that can be detected in tube coagulase test while bound coagulase is a cell wall associated protein […]

Catalase test : a test to differentiate Staphylococcus and Streptococcus

Principle:  Catalase test is done to check for the presence of enzyme catalase in bacteria that hydrolyzes hydrogen peroxide (H2O2) into water (H2O) and oxygen (O2). If the bacteria possess catalase enzyme, it’s evident by formation of bubbles in the test due to liberation of oxygen. Lack of catalase is indicated by absence of bubble production. […]

Bacteriological culture media / Types of culture media

Bacteria have to be grown for their identification and investigating other properties like antimicrobial susceptibility, test for enzyme production or test for virulent genes etc. By the use of appropriate method of isolation in culture medium, they can be obtained in pure cultures for further study. Numerous and diverse type of culture medium are available […]