Petri dishes are inverted during incubation to prevent condensation from falling into the microbes, thereby contaminating samples. Condensation in Petri dishes causes bacterial samples to spread and potentially mix with each other. Warm incubators tend to attract more condensation, so the dishes are inverted. Inversion allows water to drip down onto the lid, away from the agar, rather than onto bacteria.Continue Reading
Inversion also prevents contamination of other bacteria in the samples, in case Petri dishes were not thoroughly cleaned or other microbes happened to contaminate samples. Petri dishes can be stored up to three months in cold storage before use in an incubator.
Inverted Petri dishes also minimize the evaporation of water used to grow the samples sealed in the containers. Dishes are sealed with tape so that lids do not fall off when the inversion occurs, and the tape can be written on for labeling purposes. The apparatus can also be stacked for easy storage in an incubator.
Petri dishes were invented in 1887 by German physician Julius Petri. He improved upon the design of his mentor, Dr. Robert Koch, by inventing a small plate that has a slightly larger plate that fits over it to create smaller samples for bacterial growth. The plate allowed samples in growth media to be more easily observed under a microscope without cross-contamination from other samples. Previously, glass plates were kept under a bell jar.Learn more about Biology
Petri dishes have a variety of uses, but they are most commonly used for culturing bacteria. Petri dishes are small, clear, plastic or glass containers that can also securely contain small animals or germinating seeds. A growth medium is often placed in the bottom of a petri dish, which provides a food source for the bacteria, enabling them to reproduce rapidly.Full Answer >
Laboratories are typically stocked with frequently used equipment, such as beakers, graduated cylinders, Erlenmeyer flasks, Bunsen burners, rulers, thermometers, slides, test tubes and racks, microscopes, magnifying glasses, petri dishes, balances, clamps and ring stands. Lab users also need a handy supply of pipettes, tongs, eye droppers, stirring rods, test tube holders, clay triangles and other handling tools to reduce direct contact with chemicals and hot surfaces.Full Answer >
The advantages of agar slants include providing bacterial storage over extended periods with a minimal risk of contamination or desiccation while disadvantages involve the organisms being less observable and accessible than those in petri dishes. Agar slants also lend themselves to the identification of bacteria by characteristic patterns of movement.Full Answer >
Nonpathogens are usually harmless microbes that inhabit a living organism, such as Staphylococcus aureus and candida. Some nonpathogen microbes are bacteria that can be beneficiary for the human organism, such as lactic acid bacteria. Most nonpathogenic bacteria, lactococci and lactic acid bacteria, come from foods, such as dairy products, meat and some vegetables. These are also known as gram-positive bacteria and probiotics.Full Answer >