Category archives for Bacteriology

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 […]