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 comprises protoporphyrin IX, also called haemin or other iron-containing porphyrins. …
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 the bacteria and thus an important criterion for its identification. …
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 hemolytic strep is susceptible to the A disc, but resistant …
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). The “S” in SIM stands for sulfur. Objective To test …
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 linear fashion by α-1,4 linkages. It has 2 non-reducing ends …
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 the Enterococcus species that are salt tolerant. Objective To determine the …
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 and related compounds is a widely used method for the …
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 viscous or “stringy.” The positive string test indicates a gram …
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 enzymes, ability to utilize a particular compound etc. help them …
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 ferment the specific carbohydrate, with the production of acid or …
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. However, some organisms lack permease and appear as late or …
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 extensively used as method for biochemical differentiation of microbes. Objective …
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 acute uncomplicated urinary tract infections, particularly in young, middle aged …
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 identify and differentiate such organisms. The substrate, 4-methylumbelliferyl-β-D-glucuronide (MUG), is …
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 employed for culturing and identifying of Lactic acid bacteria especially …
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 membrane and cell wall either single flagellum or multiple flagella. …
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. However, in 1981, Faller and Schleifer modified Kovacs’ oxidase reagent …
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 its carbon source and ammonium sulfate as its nitrogen source …
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 their assimilation by bacteria, they need to be degraded. The …
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 chain fatty acids. Enzymes that break simple fat into its …
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 other catalase negative gram positive cocci. Objective To perform the …
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 to characterize several gram positive and gram negative bacteria. Objectives …
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 temperature at which growth can occur is its maximum growth temperature. …
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 of gelatinases is used as a presumptive test for the …
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. Purple Broth is used for studying carbohydrate fermentation reactions, particularly …