1. Introduction

1. Introduction

1.1 Background Research

Salmonella infection, the number one bacteria in food that leads to hospitalization and deaths (Centres for disease control and prevention, 2016) and cause an intestinal infection known as Salmonellosis. The typical symptoms include fever and diarrhea. It can be caused by Salmonella in poultry such as meat and eggs. Though Salmonella is often unknown to the public; it has caused many incidents (Food Poison Journal, 2015). Even though regular checks are conducted by the Ministry of Health or governments, Salmonella cases in Singapore are rising by 30%. In 2016, an estimate of 1042 people in Singapore was affected by Salmonella contamination. This includes a mass food poisoning case affecting 231 affected people (Qi, 2016).

Before our experiment, we conducted a survey involving 70 people, some of which are students and parents. From the results, we can infer that 70% of the respondents do not know what is Salmonella or have heard before but are unsure.
Based on background research conducted, we found out that eggs have a natural protective layer called a cuticle, otherwise known as bloom. This cuticle is removed during washing, allowing the shell to become permeable which allows bacteria on the egg or in the water to enter (Steele, L., 2015). Having known this, one of the research questions that comes to our mind is whether washing increases the chances of Salmonellosis.

Department of Poultry Science, The University of British Columbia (1969)  wrote in a chapter of the report “Bacterial Infection of Washed and Unwashed Eggs with Reference to Salmonellae” on how they soaked 1 set of eggs in a 10% solution of Formalin and dried it for 30-60 minute intervals for four hours while another set of eggs was unwashed. The bacteria on the eggshells were counted the next day. Although their experiment was different from ours, their experiment also involved the the testing of eggs after one day. They found that the proportion of the samples contaminated with bacteria beyond an average of 5-million organisms per egg was the washed eggs with 21.8% bacteria while with the unwashed eggs with 8.0% bacteria. However, as mentioned before, this experiment is different from the one we conducted and this research paper was written a long time ago.

“Statistical analysis indicated that, at a dose of 105 CFU/mL, the penetration of S. typhimurium strain 2 into washed eggs was significantly higher (p = 0.04) compared to unwashed eggs” as quoted from Axel, C (2014), editor of effect of washing and correlation between eggshell characteristics and egg penetration by various Salmonella strains. From this, we can tell that washed eggs have notably higher bacterial count than unwashed eggs. As this experiment is different from ours as they not only wash the eggs but also penetrate S. typhimurium strain into the eggs; this results can be confirmed by our experiment of washing, storing and testing the eggs with a one day incubation period.


1.2 Research Questions

The following are our research questions for the experiment:
  1. Does washing increase the chances of salmonellosis (salmonella contamination)?
  2. Does washing time affect the growth of bacteria?


     1.3 Hypothesis

Our first hypothesis is that the unwashed eggs will have a lesser amount of bacteria on the shells as compared to all the other eggs which were washed. In our research, we found information about washing eggs removing the protective layer on the shell, hence allowing more bacterial growth, therefore we have come up with this hypothesis.

Our second hypothesis is that the longer we wash the eggs under running water, the greater the number of bacteria growing on the eggshells. Therefore, the amount of washing time for each egg will differ.

Many people do not know of the effect of washing eggs on the bacterial growth, hence consume washed eggs with possibly more harmful bacteria. Our aim is that through our experiment, we can investigate the effect of washing eggs on the bacterial growth and educate people on this topic.

Our independent variable is the amount of washing. In figure 2.3 we have included data table for easy reference. We will be washing the two eggs for 10, 20 and 50 seconds each, and leaving 2 eggs unwashed.

The dependent variable is bacterial growth. Depending on the time of washing, there will be different rates of bacterial growth. This variable is also very important to our end results.

The controlled variables in our experiment can be divided into two categories: the washing and drying of eggs and the storage and incubation period.

For the washing and drying of eggs, we must first ensure the type of eggs are the same. Secondly, the type of liquid used to wash the egg, which will be tap water for all, must have the same flow rate. The environment we are washing the eggs in is also very crucial, and all washing will be done in the lab, using the lab sink. Lastly, the method of drying will be the same for eggs, which is natural drying.

For the storage and incubation period, dependant variables include the amount of time eggs are placed in the lab fridge. Thereafter, we must ensure that the amount of time the cotton swab is in contact with the egg and the agar plate is the same for each egg. Lastly, the amount of time each agar plate is in the incubator must be the same for every agar plate.

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