The Benefits of Alternate Agar Types on the Growth of Bacteria
by Misha Silverman


INTRODUCTION
    For the first few weeks of streaking plates, we only used one type of agar: nutrient agar. All seven types of bacteria were always streaked on this one agar. After a couple of weeks of this single agar streaking, we were introduced to the wonderful work of broth cultures. There were three types of broth: nutrient, lactose, and glucose. This got me thinking. If there are three types of broth media, then there should be three types of agar media. I referred back to my trusty experimental biology manual and, lo and behold, there was my answer. There are three types of agar, nutrient, lactose, and glucose, and possibilities for many more types, depending on what is added to the agar during preparations.

    The bacteria grew well on the nutrient agar which other than peptone contains a little bit of beef broth. If other nutrient were added to the agar then maybe the bacteria will grow more. My hypothesis was that upon the addition of more łnourishing˛ food the bacteria would grow better. More nutrients allow for better growth.

METHODS and MATERIALS
    My original design was to divide my agar dishes into four sections and streak a selected bacteria, E. coli, and streak in each section. I soon realized that this was not going to work. It wasnąt going to accomplish anything because there was no way to compare the streaks to a constant. My next design was to divide my dishes into three sections and then streak each section after dipping my inoculator in one section. After further thought, I realized that this too would not accomplish anything. I racked my brains for the whole weekend and came up with what I thought was the solution. I would change my experiment slightly. My experiment would now be a comparison. I would divide my dishes in half and in each half, I would streak four traces of two bacteria, E. coli and B. meg. After allowing a full day of growth in the incubator (30°), I measured the width of the bacteria at their widest parts. Each half was clearly labeled, so as not to confuse me. I chose these bacteria because they are easily differentiable. They do not look alike which is important in terms of indentification.. E. coli is more of a spotty, granular bacteria of a light yellow hue, whereas B. meg is creamy, with a light red hue.
RESULTS
    Each dish represents a day and the numbers are all in millimeters and are the averages of the four streaks. I measured the widths with a centimeter ruler .E. coli Dish 1 Dish 2 Dish 3 Dish 4 Dish 5 AVERAGE Nutrient Agar 5.25 mm 5 mm 6.25 mm 0 mm 5 mm 4.3 mm Lactose Agar 4 mm 6.25 mm 5.5 mm 4.5 mm 4 mm 4.85 mm Glucose Agar 5 mm 5.5 mm 5.25 mm 4.75 mm 5.125 mm 5.125 mm B. meg Dish 1 Dish 2 Dish 3 Dish 4 Dish 5 AVERAGE Nutrient Agar 5 mm 7.25 mm 6.5 mm 0 mm 7 mm 5.15 mm Lactose Agar 6 mm 11. 25 mm 9.5 mm 7.5 mm 8 mm 8.45 mm Glucose Agar 8.25 mm 9.5 mm 8 mm 11 mm 9.5 mm 9.25 mm

DISCUSSION
    As my results show the Glucose agar is better source of nutrition for the bacteria than the the other two. The most commonly used agar, the nutrient agar, is the worst (relatively speaking) source of nutrition. The B. meg. as a whole grew better than the E. coli, averaging 1 to 5 millimeters more in width. This means that the glucose agar is a better medium for B. meg. and B. meg. grows better than E. coli on any type of agar. I proved that there are better media that can be used other than regular nutrient agar. The above results prove my hypothesis right. More nutrients in the agar allow for better growth.

    This experiment, though good and worthwhile, but I wish I had had more time to be able to streak more differences and maybe streak two other bacteria types. That way the experiment would have been more thorough.

    Also, I found that the agar was particularly soft. I ruined countless dishes of agar by tearing into the surface. Maybe if less water were added while making it, this wouldnąt happen. Maybe less water would minimize condensation, because there was quite a lot of moisture in my dishes. I put them in the incubator upside down and they still were filled with water. This caused problems for one of my dishes, dish 4. There was so much water in the dish that it washed away the streaks. This caused the two ł0mm˛ readings. So much water had condensed that the streaks that had grown smeared away and all my data was lost.

CONCLUSION
    The more nutrients in the agar, the better the bacteria will grow. Since food and nutrients are needed to grow well, the more nutrients fill the agar, lactose and glucose, the more growth can be seen. This completely expected, being logical. Bacteria grow everywhere and on anything, but obviously bacteria have preferences of food.
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