Culturing Bacteria Lab

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When culturing bacteria in a lab, the cells must be grown on media. The purpose of the 3.1 lab was to make the media that would be required for the subsequent microbiology labs. The two major categories of media are liquid and solid mediums. Commonly, the liquid medium used for culturing E. coli, a type of bacteria, is Luria-Bertani or commonly abbreviated as LB broth. LB broth consists of water, 1% tryptone, .5% yeast extract, and .5-1% NaCl depending on the bacteria. Typically 20 grams of LB Lennox powder makes 1L of broth and 25g of LB Miller powder yields the same amount of broth. If cultured on a solid medium, E. coli is grown on LB agar. The formula to make LB agar is exactly the same as that for LB broth with the exception of an additional …show more content…
One common practice used to keep media as sterile as possible is called aseptic technique. Aseptic technique involves avoiding contact between sterile and non-sterile items, wiping down and sterilizing all surfaces, wearing latex gloves and frequently changing them, shielding a Petri plate with its lid to prevent the introduction of unwanted microbes from the surrounding air, sterilizing containers and liquid with an autoclave, using only sterile equipment and tools, and finally never putting sterile objects down on non-sterile surfaces while conducting an experiment. Aseptic technique can apply to a variety of experiments ranging from making media to culturing …show more content…
This type of media is called selective media which allows the growth of only some types of organisms and inhibits the growth of other undesired organisms. Sucrose containing agar or LBS agar (1% sucrose) helps yogurt bacteria grow. The presence of ampicillin in agar (at a concentration of 50-100 µg/mL) also known as LB/amp selects for bacteria that produce the specific ᵝ-lactamase enzyme which breaks down ampicillin. The presence of arabinose makes a protein produce a specific plasmid and is added with a final concentration of 2mg/mL to make LB/ara. Both ampicillin and arabinose must be added after autoclaving media solutions because they will break down with heat and stock solutions should be stored at -20°C for use within a year. When adding penicillin or crystal violet, the growth of Gram-positive bacteria (bacteria with high peptidoglycan content in their cell walls that pick up the Gram stain) is inhibited. If potassium tellurite or thallium acetate is added to agar, the growth of Gram negative bacteria (bacteria that do not pick up the Gram stain) is
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