(The slide shouldn’t get too hot to touch, and it should never stop as it passes through the flame.)Ĥ. Let the specimen on the slide air dry, and then heat fix it by passing the slide through a candle flame 3-4 times. Take another slide and use its edge to scrape or ‘smear’ the specimen into a very thin film of material.ģ. Make a specimen smear by placing a small amount of bacteria from one of the cultures on a clean glass slide with the inoculating needle. Sterilize your inoculating needle by placing it in a candle flame. After you have tried that, stain each of your live bacteria cultures using the following procedure:ġ. If the Gram staining procedure is done correctly, your slide should have a mixture of gram-negative and gram-positive cells as well as some neutrophils (white blood cells) with pink nuclei. Try collecting some bacteria from between your teeth (using a toothpick) and placing it on a slide with a drop of water. To practice, it is a good idea to make a ‘control’ slide. Some of the steps of the gram stain process are hard to carry out perfectly. Gram stain kit (contains crystal violet stain, Gram iodine stain, ethyl alcohol solvent, Safranin O counterstain, plain microscope slides, medicine dropper, coverslips). ![]() (You could also grow your own cultures with agar and petri dishes) Live bacteria cultures – Bacillus Cereus and Rodospirillum Rubrum.Cover accidental breaks or spills with bleach or alcohol for 10 minutes, then carefully sweep up, seal in a plastic bag, and discard. When finished experimenting, seal dishes in a plastic bag and dispose. Even then, remove the petri dish only enough to insert your implement or cover medium with bleach or 70% isopropyl alcohol. Keep petri dishes with cultured mediums closed-preferably taped shut-unless sampling or disinfecting. Work in a draft-free room and reduce airflow as much as possible. Never eat or drink during bacteria studies, nor inhale or ingest growing cultures. To minimize risk, wear disposable gloves while handling bacteria, and thoroughly wash your hands before and after. While most environmental bacteria are not harmful to healthy individuals, once concentrated in colonies, they can be hazardous. Always keep chemical bottles tightly capped. Work in a clean, well ventilated, uncluttered area where you can quickly wipe up spills. Basic safety equipment that you should wear include safety goggles (splash type), chemically resistant gloves, and a chemically resistant lab apron. The stains used for the gram stain process will discolor clothing and skin. Be sure you understand the hazards involved, the proper safety equipment to wear, and what you will do in case of a spill or contact with your skin. Always carefully read the entire label before using a chemical. Often the chemicals used to prepare slides may be toxic, corrosive or have other related hazards. Before you start, read the following safety note. Working with chemicals and bacteria can be hazardous. In part two, set up a controlled experiment to measure the effect of each type of antibiotic on each type of bacteria. In part one, perform a gram stain on bacteria cultures to determine which are gram-negative and which are gram-positive. Hypothesis: Based on your research, write a detailed hypothesis predicting the answer to the question.Įxperiment: An experiment to test your hypothesis will need two parts. ![]() Observe/Gather Data: Do some research to find information about antibiotics and gram staining, so that you can make an informed hypothesis. ![]() Question: Will four common antibiotics (Penicillin, Ampicillin, Neomycin, and Erythromycin) have the same effect on both gram-negative and gram-positive bacteria? Gram staining helps doctors make a diagnosis, but can it also help suggest a cure? What is the relationship between gram classification and antibiotic use? Do common antibiotics interact differently with gram-positive and gram-negative bacteria? Answer these questions through experimentation. For example, the bacteria that causes scarlet fever is gram-positive, while that which causes typhoid or cholera is gram-negative. Even the simple determination that a bacteria specimen is gram-positive or gram- negative can direct a doctor in diagnosis, as different bacteria cause different diseases. In the process, he discovered that bacteria could be divided into two different groups - one that retained a stain, called ‘gram-positive,’ and one that didn’t, called ‘gram-negative.’ His unique method for identifying these two groups became the first step in any bacterial identification process. In 1884 Hans Christian Gram, a Danish bacteriologist, attempted to find a universal stain that would work with all bacteria. Ever heard about gram staining and antibiotics? Here’s how it started.
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