When in doubt, be sure to clearly read the instructions and ask for help if needed either consult a teacher or call the technical help line of the agar kit supplier. The formulation for LB Luria Bertani agar is: 9.
If using tablets, dissolve 10 tablets per ml of water. For agar powders, dissolve by microwaving, 6. Stack agar plates upside down in the refrigerator. Do Not Freeze! The purpose of placing the plates upside down is to prevent condensation from dripping down onto the agar surface which could then facilitate movement of organisms between colonies. Place each Petri dish inside a zip lock bag to prevent drying out and to control odors. Turn the plates upside down and put them in a warm place.
Bacterial growth should start to become visible in days. For those growing bacteria at home for example, investigating bacteria growth at various places around the house , you may use a homemade "light bulb incubator" in place of a laboratory incubator.
Once the Petri dishes have been taped shut, they should not be opened again. All microorganisms grown during the experiment should be killed before discarding. The best way to dispose of bacterial cultures is to pressure sterilize them in a heat stable biohazard bag. If autoclaves or pressure cookers are not available or large enough to make this convenient, an alternative is to bleach the plates.
Let them sit and soak overnight in the bleach solution before disposing of them. Please note that the bleach solution is corrosive and needs to be thoroughly removed afterwards. In addition, the plates can be incinerated if access to an incinerator is available. Dorland, W. Dorland's Medical Dictionary. Please follow the item description at the bottom, next to the catalog number, and not the picture caption, which says non-nutrient agar. Menu Science Projects. Project Guides.
View Site Map. Science Projects. Grade Levels. Examples of standard general purpose media that will support the growth of a wide variety of bacteria include nutrient agar, tryptic soy agar, and brain heart infusion agar. A medium may be enriched , by the addition of blood or serum.
Examples of enriched media include sheep blood agar and chocolate heated blood agar. Selective media contain ingredients that inhibit the growth of some organisms but allow others to grow.
For example, mannitol salt agar contains a high concentration of sodium chloride that inhibits the growth of most organisms but permits staphylococci to grow. Differential media contain compounds that allow groups of microorganisms to be visually distinguished by the appearance of the colony or the surrounding media, usually on the basis of some biochemical difference between the two groups. Blood agar is one type of differential medium, allowing bacteria to be distinguished by the type of hemolysis produced.
Some differential media are also selective, for example, standard enteric agars such as MacConkey and EMB agars, which are selective for gram-negative coliforms and can differentiate lactose-fermenting and non-lactose-fermenting bacteria. Several examples of commonly used bacteriological media, as well as examples with one or more types of bacteria cultured on them are shown below. Carefully examine the plates and observe the colony morphology, colors, and patterns of growth or no growth that occurs.
This information can be valuable in the preliminary identification of pathogens in case studies. Observation of the hemolytic reactions on sheep blood agar is a very useful tool in the preliminary identification of bacteria, particularly streptococci. The types of hemolysis are defined as follows:. Streptococcus pyogenes , S. Tryptic Soy Agar - uninoculated. Tryptic Soy Agar - Escherichia coli. Tryptic Soy Agar - Pseudomonas aeruginosa Note the blue-green color due to pyocin production by the bacteria.
There are many other types of agar plates that can select for or differentiate between specific species of bacteria or other microorganism. Mannitol salt agar MSA selects for organisms that ferment mannitol by turning the plate yellow through a pH change. MSA also differentiates between the pathogenic and non pathogenic type of Staphylococci. Sabouraud dextrose agar SDA allows growth of fungi, yeasts and mold and has a low pH, preventing growth of bacteria.
Sarah Quinlan has experience writing for various websites on science, biology, veterinary science, health and medicine. For over seven years she has worked as a scientist in various biological fields where she has written and contributed to multiple manuscripts that have been published in scientific journals.
The Chemical Composition of Nutrient Agar. Five Steps to Prepare Agar Slants. What Are Agar Slants? Agar volume dispensed into plates is reproducible and contamination rate is low compared to hand-pouring of agar in open laboratory. When possible, use laminar air flow hood along with automated dispenser. Pour same quantity of agar into all plates so that same height of agar will be presented to spiral plater stylus tip to maintain contact angle.
Agar plates should be level during cooling. Let agar solidify on level surface with poured plates stacked no higher than 10 dishes. Place solidified agar plates in polyethylene bags, close with ties or heat-sealer, and store inverted at Bring prepoured plates to room temperature before inoculation. As described in Chapter 1, select that part of sample with smallest amount of connective tissues or fat globules.
Spiral plater inoculates surface of prepared agar plate to permit enumeration of microorganisms in solutions containing between and , microorganisms per ml. Operator with minimum training can inoculate 50 plates per h. Within range stated, dilution bottles or pipets and other auxiliary equipment are not required. Required bench space is minimal, and time to check instrument alignment is less than 2 min. Plater deposits decreasing amount of sample in Archimedean spiral on surface of prepoured agar plate.
Volume of sample on any portion of plate is known. After incubation, colonies appear along line of spiral. If colonies on a portion of plate are sufficiently spaced from each other, count them on special grid which associates a calibrated volume with each area. Estimate number of microorganisms in sample by dividing number of colonies in a defined area by volume contained in same area.
Studies have shown the method to be proficient not only with milk 4 but also with other foods 7, Check stylus tip angle daily and adjust if necessary. Use vacuum to hold microscope cover slip against face of stylus tip; if cover slip plane is parallel at about l mm from surface of platform, tip is properly oriented.
Liquids are moved through system by vacuum. Clean stylus tip by rinsing for 1 s with sodium hypochlorite solution followed by sterile dilution water for 1 s before sample introduction. This rinse procedure between processing of each sample minimizes cross-contamination. After rinsing, draw sample into tip of Teflon tubing by vacuum applied to 2-way valve. When tubing and syringe are filled with sample, close valve attached to syringe.
Place agar plate on platform, place stylus tip on agar surface, and start motor. During inoculation, label petri plate lid. After agar has been inoculated, stylus lifts from agar surface and spiral plater automatically stops. Remove inoculated plate from platform and cover it. Move stylus back to starting position. Vacuum-rinse system with hypochlorite and water, and then introduce new sample.
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