Micro Lab Test

MacConkey Agar

to detect and differentiate among gram-negative enteric bacilli, based on their ability to grow on the medium and to ferment lactose. bacteria that utilize lactose and produce acids will have colonies that are pink to red in color because of a color change in neutral red, the pH indicator that is also in the medium. Colonies of non-lactose fermenting bacteria are colorless.

Citrate Utilization Test

to determine if a bacterium can utilize citrate as its sole source of carbon and energy if the bacteria utilize the citrate the byproduct CO2 combines with Na+ in the medium to form NaCO3, an alkaline compound. pH indicator bromothylmol blue turns blue in a alkaline pH. Change in color from green to blue indicates a positive test.

Nitrate Reduction Test

to determine if a bacterium is able to reduce nitrate ions to either nitrite ions or to nitrogen gas. nitrate present medium will turn pink or red, no color change is a negative test. Use nitrate reductase to create nitrogen ion in water react with agent a or b causes change in color. Use zinc to reduce nitrate ions causing a reaction

Oxidation-fermentation Glucose Test

to determine if a gram-negative bacterium uses fermentation or areobic respiration in utilizing a particular sugar for energy if fermentation takes place and acids are present the bromothylmol blue will turn yellow in the medium if no acids are present (aerobic respiration) the medium appears green and fermentation of sugar did not take place.

Oxidase Test

to determine if bacteria have cytochrome oxidase, a participant in electron transport during respiration; change from dark blue to light purple is positive test, yellow is negative

Motility Test

to determine if bacteria is motile. cells swim away from stab indicates motility non-motile bacteria will grow only along the stab also use hanging drop slide prepartion- not suitable for pathogenic bacteria because of the risk of enviornmental contamination.

Urea Hydrolysis Test

to determine the ability of a bacterium to hydrolyze bright pink in medium and basic pH is positive negative test is no color change urea is broken down into carbon dioxide and ammonium

Fat Hydrolysis Test

to determine the ability of a bacterium to hydrolyze a triglyceride, a type of lipid to use triglycerides for food and energy, bacteria must secrete enzymes called lipases; zone of clearance is positive

Amino Acid Decarboxylase Test

to determine the ability of a bacterium to remove the carboxyl group from an amino acid (decarboxylation) positive is purple, negative is yellow

Phenylalanine Deamination Test

to determine the ability of a baterium to remove the amino group from the amino acid phenylalanine. a dark green color appears in a positive test. If no phenylpyruvic acid is present, the medium appears yellow, the color of FeCl3 (ferric chloride) detection agent reacts with phenylpyruvic

Gelatin Hydrolysis Test

to determine the ability of bacteria to hydrolyze gelatin, gelatinase is the enzymed used; breaks gelatin down into amino acids and peptides; positive is liquid, negative is solid

Fermentation of Carbohydrates

to determine the ability of some bacteria to ferment a particular carbohyrate in this test acid production is identified by a change in the color of the phenol red; yellow is a positive test, red is negative stayed the same

Voges-Proskauer Test

to determine the ability of some bacteria to ferment glucose via butanediol fermentation] VP reagents react with acetoin in the presence of oxygen to form a red product-positive test. No color change after addition of the VP reagent is a negative test.

Methyl Red Test

to determine the ability of some bacteria to ferment glucose via mixed-acid fermentation when methyl red is added to the medium and pH is 4.5 and below(more acidic due fermentation of glucose producing acids, alcohols and gases) the methyl red reagent remains red in color-positive result. At higher pH the color may be orange or yellow-negative test

Indole Test (Tryptophan Degradation)

to determine the ability of some bacteria to split the amino acid tryptophan into indole and pyruvic acid. some bacteria can use tryptophan as a source of energy by degrading the amino acid to get pyruvate. indole is a byproduct not used by the bacteria. appearance of a red layer at the top of the tube-positive test absence of red layer-negative test: tryptophan was not hydrolized use kovacs reagent

Kirby-Bauer Technique

to determine the sensitivity of a bacterium to several antibacterial medicines. A zone of growth inhibition may appear around the disk. The diameter of this zone indicates susceptibility or resistance(small zone of growth) of the tested bacterium to the antibacterial medicine.

Litmus Milk Reaction

to differentiate among bacteria as to their ability to utilize lactose, protein, and litmus in litmus milk. Bacteria that ferment lactose form organic acids. Presence of Curds formed when more acidic. The resulting acid pH turns litmus pink. Negative test is no change in color.

Triple Sugar Iron (TSI) Agar Test

to differentiate among the gram-negative enteric bacilli as to their ability to ferment glucose, lactose, and sucrose and to produce H2S; acidic is yellow, basic pH is red

Catalase Test

to direct the presence of catalase, an enzyme that degrades hydrogen peroxide separates hydrogen peroxide into water and oxygen; presence of bubbles is a positive test

Starch Hydrolysis Test

to distinguish among bacteria in terms of their ability to hydrolyze (digest) starch grams iodine shows whether the bacteria digested starch or not by showing a black(no digestion) or white(digestion) color

Casein Hydrolysis Test

to distinguish among bacteria in terms of their ability to hydrolyze casein, the major protein in milk caesinase enzyme is being digested. clear zone around bacteria is a positive test

Acid fast Stain

to distinguish two groups of bacteria based on the lipid content in their cell walls: acid-fast and non-acid-fast acid fast is red and non acid fast is blue- carbylfusion is used

Gram Stain

to identify most bacteria by dividing them into two groups: gram-negative and gram-positive observe under microscope for cell shape, arrangement, and size grams iodine: fixes stain into bacteria safranin: counter stain, gram negative is pink, gram positive is purple crystal violet: stains (primary stain) acid alcohol: decolorizing agent

Eosin Methylene Blue (EMB) Agar

to isolate and differentiate gram-negative enteric bacilli significant acid results in dark blue colonies with a greenish metallic sheen. lower acid production from fermentation of the sugars by some bacteria unable to ferment these disaccharides are colorless or take on the color of the medium.

Blood Agar Plate

to isolate and support the growth of fastidious bacteria to differentiate among bacteria based on their ability to lyse(swell/burst) red blood cells. In B-hemolysis bacteria secrete enzymes that completely dismantle the RBC's . In a-hemolysis partial disruption of the RBC's by the bacteria results in a greenish hue around a colony Nonhemolytic bacteria do not damage RBC's and are sometimes called y-hemolytic.(gamma)

Mannitol Salt Agar

to isolate bacteria based on their salt tolerance and differentiate among these isolates for mannitol fermentation. Acid-produced from fermentation of mannitol turns the pH indicatior phenol red from red to yellow. non-pathogenic staphylococci do not have yellow zones around their colonies.

Phenylethyl Alcohol (PEA) Agar

to isolate gram-positive bacteria from a specimen containing a mixture of gram-positive and -negative bacteria. PEA inhibits or slows the growth of gram-negative bacteria by interfering with DNA synthesis. Gram-positive bacteria will grow in presence of PEA.

Simple Stain

to stain bacteria so they can be seen more clearly under the microscope determine the shape, arrangement and size of bacteria

Negative Stain

to view bacteria by creating a dark background to view bacterial cells that are difficult to stain with basic dyes to view bacteria that are fragile and easily distorted by heat-fixation nigrosin stain is used

Capsule Stain

to view bacterial capsules or slime layers use nigrosin let dry before safranin or crystal violet

Endospore Stain

to view bacterial endospores under the microscope to observe the location of an endospore in a sporulating cell Staining reagents: malachite green, safranin endospores are formed in mostly gram positive bacteria