By Prof Daniel Asrat Introduction The objective of Hydrogen Sulphide Test is to determine whether the microbe reduces sulfur-containing compounds to sulfides to produce hydrogen sulfide gas.Some bacteria have the ability to reduce sulphur to hydrogen sulphide. It is a colorless gas, which reacts with iron (ferrous salts) to produce black precipitates of ferrous sulphide.It also reacts with lead … Read more
By Prof Daniel Asrat Introduction The Triple Sugar Iron (TSI) test is a microbiological test roughly named for its ability to test a microorganism’s ability to ferment sugars and to produce hydrogen sulfide.[1] It is often used to differentiate enteric bacteria including Salmonella and Shigella. The TSI slant is a test tube that contains agar, a pH-sensitive dye (phenol red), 1% lactose, 1% sucrose, 0.1% glucose, and sodium thiosulfate and ferrous sulfate or ferrous ammonium sulfate. All … Read more
By Prof Daniel Asrat Principle Some bacteria have the ability to deaminate the amino acid phenylalanine, as they can produce the enzyme ‘phenylalanine deaminase’.This enzyme deaminates phenylalanine by removing its amino group, thereby producing phenylpyruvic acid (a keto acid) and ammonia (NH3). Phenylpyruvic acid forms green colour with ferric chloride solution. In the phenylalanine deaminase … Read more
By Prof Moses Joloba Principle Some bacteria have the ability to hydrolyse (breakdown in presence of water) urea to NH3 and CO2, as they can produce the enzyme ‘urease’. NH3 is alkaline (basic), due to which, it increases the pH changing the color of phenol red from yellow to pink. In the urease test, the test bacteria … Read more
By Prof Moses Joloba Introduction The indole test is a biochemical test performed on bacterial species to determine the ability of the organism to convert tryptophan into indole. This division is performed by a chain of a number of different intracellular enzymes, a system generally referred to as “tryptophanase.” Indole is generated by reductive deamination from tryptophan via the intermediate molecule indolepyruvic acid. Tryptophanase catalyzes the deamination … Read more
By Prof Moses Joloba Principle Some bacteria have the ability to utilize glucose and convert it to a stable acid like lactic acid, acetic acid or formic acid as the end product.These bacteria initially metabolise glucose to pyruvic acid, which is further metabolized through the ‘mixed acid pathway to produce the stable acid. The type … Read more
By Prof Moses Joloba Introduction Gram staining is the most important differential staining method used in microbiology. Gram stain or Gram staining, also called Gram’s method, is a method of staining used to distinguish and classify bacterial species into two large groups: gram-positive bacteria and gram-negative bacteria. The name comes from the Danish bacteriologist Hans Christian Gram, who developed the technique. 1) Gram-positive Bacteria: … Read more
By Prof Moses Joloba Objective The Objective of capsule staining is to observe bacterial capsule by distinguishing capsular material from the bacteria cell.In some bacteria, the cell wall is surrounded by a viscous cell envelope called ‘capsule’. It is made of polysaccharide, glycoprotein or polypeptide.When the capsule is too thin to be observed under light … Read more
By Prof Mariam Mirambo Elements Of Comparison Staphylococcus Streptococcus Cellular Arrangement Spherical cells in clusters (grape like clusters). Spherical or ovoid cells in chains or pairs. Fission/Division Irregular division in all three planes. Division in one linear direction. Catalase Test Positive (Presence of catalase enzyme) Negative Halotolerance Halotolerant. Can tolerate upto 8% salt concentration. Inhibited … Read more