Day 1

Pathogenic bacteria might hide in our daily environment and can cause infectious diseases and outbreaks. The trays used by different canteen are often not well cleaned due to the large size of students in the canteen. Bacteria might thrive on the surface of the trays in the canteen due to the warm climate in Singapore.

Learn how to isolate and cultivate bacteria from everyday environment.

Theoretical Background
In this experiment, students will collect samples from surface of food trays from different NTU canteens and cultivate them in liquid nutrient medium and then transfer to petri dish. Culture medium is defined as a solid or liquid preparation used for the growth, transport, and storage of microorganisms. The effective culture medium must contain all the nutrients required for the growth of the microorganism. Specialized media are widely employed for the isolation and identification of microorganisms. Selective media allows the growth of certain type of organisms, while inhibiting the growth of other organisms. This selectivity is achieved in several ways. For example, organisms that have the ability to utilize a given sugar are screened easily by making that particular sugar the only carbon source in the medium for the growth of the microorganism. Like-wise, the selective inhibition of some types of microorganisms can be studied by adding certain dyes, antibiotics, salts or specific inhibitors that will affect the metabolism or enzymatic systems of the organisms. For example, media containing potassium tellurite, sodium azide or thallium acetate at different concentrations of 0.1 - 0.5 g/l will inhibit the growth of all Gram-negative bacteria. Media supplemented with the antibiotic penicillin concentration 5-50 units/ml or crystal violet 2 mg/l inhibit the growth of Gram-positive bacteria. Tellurite agar, is used to select for Gram-positive organisms, and nutrient agar supplemented with the antibiotic penicillin can be used to select for the growth of Gram negative organisms.
Eg., Mannitol salt agar, Hektoen enteric agar (HE), Phenylethyl alcohol agar

Differential media are widely used for differentiating closely related organisms or groups of organisms. Because of the presence of certain dyes or chemicals in the media, the organisms will produce certain characteristic changes or growth patterns that are used for identification or differentiation of microorganism.

Eg., Mac Conkey (MCK) agar, Eosin Methylene Blue (EMB) agar

What did we do today?
We had to use the samples of the collected bacteria and transfer them to the petri dishes. Then, we set out to find samples on our own. I had collected my sample from the glass outside the building.

What did we learn today?
Bacteria is all over, and there is probably no way you can get rid of it completely. Some types of bacteria can survive in the harshest conditions, including in ice and lava. They can also be beneficial to humans, when used properly. They are used industrially, as well as in the production of many things.

How do I feel about today's activities?
I felt excited and nervous when I saw the lab. It was my first time being in an actual laboratory, with all the equipment. Before this, I had experienced working with antibiotics, I think, as part of our school program. I had to go through many rounds of mistakes, including spilling the solution on my lab partner's paper. It was truly tough, and I think that it was worth it in the end.

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