Food Cultures

Introduction: This experiment is performed to find any pathogens that is in produce in which people consume every day. We are attempting to determine the most effective way to wash produce so that there is the fewest amount of pathogens on it. In this case, we will be looking at pathogens that is on strawberries.

Depending on the pathogens, it can be harmful for human; therefore, it is important to know what is contained in our food. A pathogen “is a biological agent that causes disease or illness to its host.” (www.sciencedaily.com/terms/pathogen.htlm)

There are many ways foods can be in contact with pathogens. First of all, the air and soil has many pathogens and bacteria floating in it that can easily come in contact with our food. If the food is packaged, there may be pathogens from the packaged materials. Also pesticides used to preserve foods is very commonly used.

Materials and Methods: First I chose to use a strawberry to determine the possible pathogens that could be on this piece of fruit. With a sterile swab that was dipped in distilled water, I swabbed a small section towards the top of the strawberry. I then took the swab and transferred it to my already sectioned agar plate that is labeled H2O. Next I used another sterile swab dipped in vinegar and swabbed a lower section of the fruit and transferred it to the appropriate section on my agar plate. Lastly I swabbed an even lower section of the strawberry with another sterile swab with lemon and transferred it to the appropriate section on my agar plate. After transferring all three washes to the agar plate, I placed the plate in incubation at 37 degrees until the next class.

During the next class several colonies have grown. Many of the colonies were white, circular and of all different sizes. Some of the colonies contained were yellow and circular. Taking one of the larger white, smooth colonies I transferred it to a slide by using the heat sterilized loop and distilled water. Once the sample is on the slide, I poured crystal violet on the sample and let it sit for one minute, then rinsing the sample with water. Next I poured the sample with iodine and let it sit for one minute then rinsing it off with water. Next I poured acetone on the sample and letting it sit for ten seconds then rinsing it with water. Lastly, I used the counterstain safranin on the sample and letting it sit for 45 seconds then rinsing it with water. To get rid of excessive water, I blotted the slide with bibulous paper. Lastly the slide needs to be heat fixed by passing the slide through the flame of a Bunsen burner several times. To be able to see the pathogen close up, the slide needs to be under oil immersion magnification.

Data: After 48 hours of the plate in inoculation, I found that vinegar cleaned my sample the best. The section in which only water is used had too many colonies to count. Most of the colonies were circular in size, white/clear in color. One colonies had some yellow coloring within it. The section where lemon is used had four small, yellow, circular colonies. The rest included 22 small circular white/clear colonies. The vinegar only contained six colonies. All of them were white, circular, and medium in shape.

| # of colonies | Edge | Color | Shape | H2O | Too many to count | Irregular | White/clear, few yellow | Circular | Lemon | 26 | Irregular | White/clear, few yellow | Circular | Vinegar | 6 | Irregular | White/clear | Circular |

Conclusion: In my hypothesis I thought that the acidity of the vinegar would be one of the key factors to help the fruit become pathogen free. I know that vinegar is used as a cleaning agent. I also know that lemon is also used as a cleaning agent but vinegar seems to be the more acidic of the two substances.

As a result of the experiment, my hypothesis is correct. It appears that vinegar portion of the agar plate contained the least amount of colonies by a landslide from the other washes.

I do not think that I would change too much from the first experiment. I felt that I maintained a sterile technique and was diligent in my execution. Perhaps I could have used a large area of the strawberry with each wash to pick up more pathogens or I could have used more than one strawberry because the strawberries were packaged closely together.P