Lactose Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Lactose and links to relevant pages within the course.
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| The colonies shown in the blood (BAP) agar (upper) and MacConkey (MAC) agar (lower) biplate are a 24 hour growth from an aerobic blood culture bottle that became positive at 12 hours after inoculation. The appearance of the colonies on MAC agar rules out the following two bacterial species: | View Page |
| Clostridium Quad Plate Key reactions for the identification of Clostridium septicum are demonstrated in the two quadrant plates shown in the images to the right. Included in the upper image are reactions for milk (casein) proteolysis (12 o'clock quadrant), glucose fermentation, DNAse hydrolysis, and starch hydrolysis respectively reading clockwise. The media in the quadrant plate shown in the lower image include gelatin hydrolysis (2 o'clock quadrant) and fermentation of each of mannitol, lactose, and rhamnose respectively, reading clockwise. Milk (casein) hydrolysis and glucose fermentation are key reactions for the identification in the upper plate, including no proteolysis of milk, fermentation of glucose (yellow red color along the inoculation streak), positive DNAse (reddish clearing around the streak) ,and a negative reaction for starch. Key reactions in the lower plate include hydrolysis of gelatin, fermentation of lactose (yellow pigment), and negative reactions for mannitol and rhamnose (no pigment). Most strains of C. perfringens hydrolyze starch and produce proteolysins of milk, the key reactions that distinguish C. septicum (negative). Reactions to the other tests do not distinguish between the two. | View Page |
| Urine Glucose Analysis The analysis for glucose on a chemical reagent strip is a double-sequential enzyme reaction, utilizing the glucose-oxidase/peroxidase method. In the first reaction, glucose oxidase catalyzes the oxidation of glucose to gluconic acid and hydrogen peroxide. Then, the peroxidase catalyzes the oxidation of a chromogen by the hydrogen peroxide to form a colored product. The chemical reagent strip glucose pad is then analyzed and recorded at the set interval stated by the manufacturer.This method does not react with lactose, fructose or galactose. Study the dipstick color chart in your laboratory to become familiar with the range of color changes. NOTE: The urine specimen should be analyzed while at room temperature for these enzyme reactions to occur properly. | View Page |
| Glucose Test The test for glucose is a double sequential enzyme reaction, utilizing the glucose-oxidase/peroxidase method. In the first reaction, glucose oxidase catalyzes the oxidation of glucose to gluconic acid and hydrogen peroxide. Then, the peroxidase catalyzes the oxidation of a chromogen by the hydrogen peroxide to form a colored product. This method does not react with lactose, fructose or galactose. Study the dipstick color chart to become familiar with the range of color changes. The urine specimen should be at room temperature for these enzyme reactions to occur properly. | View Page |
| Reducing Sugars Although glucose is the sugar most commonly tested for in urine, normal human urine can contain small amounts of galactose, lactose, fructose, xylose, and other pentoses. Galactosuria, an abnormal amount of galactose in the urine, occurs in infants with a congenital metabolic defect. Lactose may be found in the urine of nursing women and during late pregnancy. All of these sugars, including glucose, are reducing substances. | View Page |
| Which of the following is used as the indicator in the rapid carbohydrate utilization tests: | View Page |
| Match the differential/ selective enteric medium with its characteristic indicator, fermentable, and bacteriostatic. | View Page |
| MacConkey agar contains all of the following except : | View Page |
| The red/pink color of the colonies (E. coli) seen on this MacConkey Agar Plate is an indication of: | View Page |
| The selective medium XLD is seen in this illustration. What is the significance of the black colonies observable on this plate: | View Page |
