Haemophilus spp are small, pleomorphic, gram-negative bacilli or coccobacilli with random arrangements. A clinically important species of the genus, influenzaeis a fastidious organism which grows best at 35-37°C with ~5% CO2 and in the presence of special accessory growth factors called X and V factors. X factor … Read more
Most bacteria have the ability to ferment carbohydrates, particularly sugars. Among them, each bacteria can ferment only some of the sugars, while it cannot ferment the others. Thus, the sugars, which a bacteria can ferment and the sugars, which it cannot is the characteristic of … Read more
Although bacitracin susceptibility has routinely been used for the presumptive identification of group A streptococci, it has been observed that streptococcal groups vary in their susceptibilities to Taxo A (bacitracin, 0.04 units) and SXT (trimethoprim [1.25 mg] plus sulfamethoxazole [23.75 mg],) disks. Group A beta … Read more
SIM medium (Sulphide Indole Motility medium) which is a combination differential medium that tests three different parameters, Sulfur Reduction, Indole Production and Motility. As the name suggests, it is commonly used to test a microbe for the ability to produce the gas hydrogen sulfide (H2S). … Read more
Starch is a complex polysaccharide found abundantly in plants and usually deposited in the form of large granules in the cytoplasm of the cell. Starch consists of 2 components—amylose and amylopectin, which are present in various amounts. The amylose consists of D-glucose units linked in a … Read more
The ability of the bacteria to grow in the presence of variable amount of Sodium Chloride (NaCl) has been used to characterize several bacteria. It takes into account the organism’s ability to tolerate various osmotic concentrations. E. faecalis, E. zymogenes, E. liquifaciens, and E. durans are among … Read more
Biochemical tests are the tests used for the identification of bacterial species based on the differences in the biochemical activities of different bacteria. Bacterial physiology differs from one type of organism to another. The ability of bacteria to form organic compounds by metabolizing certain carbohydrates … Read more
The KOH String Test relies on the differential resistance to 3% potassium hydroxide between gram positive and negative cells, where a portion of a colony is mixed with a small volume of 3% KOH. If the cells lyses, the liberated cellular DNA makes the mixture … Read more
Biochemical tests are the tests used for the identification of bacteria species based on the differences in the biochemical activities of different bacteria. Bacterial physiology differs from one type of organism to another. The differences in carbohydrate metabolism, protein metabolism, fat metabolism, production of certain … Read more
Fermentation media are used to differentiate organisms based on their ability to ferment carbohydrates incorporated into the basal medium. Phenol Red Broth Medium with various added carbohydrates serves as a differential medium by aiding in differentiation of various species and genera by their ability to … Read more
The ability of bacteria to ferment lactose depends on two enzymes, permease and beta-galactosidase. Permease allows lactose to enter the bacterial cell wall, where it is then broken down into glucose and galactose by beta-galactosidase. The glucose and galactose can then be metabolized by the bacteria. … Read more
Carbohydrates are organic molecules that contain carbon, hydrogen and oxygen in the ratio (CH2O)n. Organisms use carbohydrate differently depending upon their enzyme complement. The pattern of fermentation is characteristics of certain species, genera or groups of organisms and for this reason this property has been … Read more
Novobiocin is an aminocoumarin antibiotic, produced by the actinomycete Streptomyces nivens, with antibacterial property. In 1975, Kloos and Schleifer reported a simplified scheme for differentiating coagulase-negative Staphylococcus spp. which included a novobiocin disk test. Staphylococcus saprophyticus, a gram positive coagulase negative Staphylococci, is an uropathogenic bacterium that causes … Read more
It has been reported that the enzyme β-glucuronidase is present in most strains of E. coli (97%).Organisms other than E. coli (e.g., Salmonella, Shigella, Staphylococcus, Streptococcus, etc.) also possess the enzyme β-glucuronidase. Hence, the detection of the β-glucuronidase enzyme is commonly employed in laboratories to … Read more
The MRS formulation was developed by de Man, Rogosa and Sharpe to replace a variable product (tomato juice) and, at the same time, provide a medium which would support good growth of lactobacilli in general. Hence, MRS agar and broth given to their superiority are commonly … Read more
Motility is the ability of an organism to move by itself by means of propeller-like flagella unique to bacteria or by special fibrils that produce a gliding form of motility. Motile bacteria move using flagella, thread like locomotor appendages extending outward from the plasma … Read more
Microdase Disk is a reagent-impregnated disk recommended for use in qualitative procedures to aid in the differentiation of Staphylococcus from Micrococcus by the detection of the oxidase enzyme. The oxidase method was originally described by Kovacs in 1956 as a method of differentiating gram-negative bacilli. … Read more
Malonate test is a colorimetric test of the ability of bacteria to use malonate as a source of carbon, the endpoint of which is the production of alkaline metabolites that induce a color change. Objectives To test the ability of the organism to utilize malonate as sole source of carbon and energy for growth. To differentiate organisms on the basis of malonate utilization. Principle An organism that simultaneously can utilize sodium malonate as … Read more
Lipids are high-molecular-weight compounds possessing large amounts of energy. Once assimilated into the cell, they are metabolized through aerobic respiration to produce cellular energy, adenosine triphosphate (ATP). The components may also enter other metabolic pathways for the synthesis of other cellular protoplasmic requirements. However, before … Read more
Lipid is the general term used to describe all types of fats. Fats are formed by ester linkage between three molecules of fatty acids and one molecule of glycerol. Simple fats are known as triglycerides or triacylglycerols. Triglycerides are composed of glycerol and three long … Read more
Leucine amino peptidase (LAP) test is a rapid test for detection of enzyme leucine aminopeptidase. Leucine- β- napthalamide impregnated disk serves as a substrate for the detection of leucine aminopeptidase. This test is usually used, in conjunction with other tests, for the identification of streptococci and … Read more
Phosphatidylcholine or simply, lecithin is a substance widely distributed in animal tissues, egg yolk, and some higher plants, consisting of phospholipids linked to choline. Some microorganisms possess lecithinase, also called phospholipase C, which is an enzyme that splits the phospholipid lecithin. Such lecithinase activity is used … Read more
Microbes can be roughly classified according to the range of temperature at which they can grow. The growth rates are the highest at the optimum growth temperature for the organism. The lowest temperature at which the organism can survive and replicate is its minimum growth temperature. The highest … Read more
Gelatin is a protein derived from the connective tissues of vertebrates, that is, collagen. It is produced when collagen is boiled in water. Gelatin hydrolysis detects the presence of gelatinases. Gelatinases are proteases secreted extracellularly by some bacteria which hydrolyze or digest gelatin. The production … Read more
The ability of bacteria to form organic compounds by metabolizing certain carbohydrates and related compounds is a widely used method for the identification of microorganisms. Different fermentation media are used to differentiate organisms based on their ability to ferment carbohydrates incorporated into the basal medium. … Read more
Deoxyribonucleic acid (DNA) is a large polymer of nucleotides that is way too large to enter the cell membrane. In order to utilize external DNA, bacteria cells secrete exoenzymes (DNases) outside of the cell that hydrolyze DNA into nucleotides. The nucleotides can then move across the cell … Read more
Cetrimide is a quaternary ammonium salt, which acts as a selective agent and inhibits most bacteria by acting as a cationic detergent (Cetyltrimethylammonium bromide). Cetrimide when added into a culture medium results into a selective solid medium recommended for use in qualitative procedures for selective … Read more
Casein, the major milk protein, is a macromolecule composed of amino acid subunits linked together by peptide bonds (CO—NH). It makes around 85% of the protein found in milk as well as the white color of milk. Casein is way too large to enter the … Read more
Esculin is a glycosidic coumarin derivative (6-beta-glucoside-7-hydroxy-coumarin). The two moieties of the molecule (glucose and 7-hydroxycoumarin) are linked together by an ester bond through oxygen. Many bacteria can hydrolyze esculin, but few can do so in the presence of bile. Thus the bile esculin test is … Read more
Butyrate discs are employed in the microbiology lab for demonstrating the enzymatic hydrolysis of bromo-chloro-indolyl butyrate. The Test Disc is used for rapid detection and qualitative procedures of butyrate esterase for presumptive identification of Moraxella catarrhalis. Moraxella catarrhalis is recognized as a significant pathogen whose isolation … Read more