Biology Microbiology assignment

Food Safety HOL #12:

Maricel Perez Torres

08/23/2025

Microbiology Lab: Wounds and Digestive System Infections

Unit 4 Week 12

Abstract

One paragraph that summarizes the report

· One paragraph that summarizes the report (no longer than a paragraph)

· Belongs at the very beginning of the paper, but should be written last

· Concise description of the experimental objectives, results, and conclusions

· Includes why the experiment was performed; what problems were addressed; what major conclusions were found; and what major conclusions were drawn.

· Does not include general background information.

· Uses proper terminology for your course (examples include: pH, dominant, nucleotide, contamination, X or Y-linked, etc.)

Introduction and Background

This study is being conducted to emphasize the importance of food safety and its impact on public health. Foodborne illnesses remain a leading cause of sickness and death worldwide, yet many cases are preventable through proper food handling, storage, and preparation. Understanding how pathogens contaminate food and learning effective prevention measures are essential for maintaining health in our households. Furthermore, educating individuals about safe practices at home and in food service settings helps reduce the risk of outbreaks and lowers healthcare costs. Ultimately, this study aims to enhance knowledge of food safety and promote its practical application in daily life to prevent foodborne diseases and protect overall well-being.

In this experiment, we will analyze the types of pathogens present on unwashed lettuce compared to lettuce that has been properly washed. Additionally, we will investigate the microbial growth in milk after the container has been opened and stored in the refrigerator for 7 days, compared to a sealed container that has been refrigerated for the same period. This study aims to demonstrate the effects of washing and exposure on food safety and the potential for microbial contamination.

We aimed to prove that washing lettuce and keeping milk containers sealed will reduce microbial contamination compared to unwashed lettuce and opened milk.

Milk consumption is widespread in many areas of society, making it a common source of infection, especially when not handled, stored, or processed adequately. Prevention of transmission of milk contaminants is a reasonably easy task and can be achieved with minimal effort.  Some milk-related diseases are endemic in certain underdeveloped countries. As is the case with Brucellosis (Kapoor et al., 2023). 

Microbes found in raw milk can be part of beneficial flora. An example of this is the type of beneficial organism, Lactobacillus. Also, we may discover spoilage organisms such as Pseudomonas. The third type of organisms found on milk are pathogenic. These include, among many others, Brucella melitensis, the causative organism of Brucellosis (Kapoor et al., 2023).

Raw milk can cause 840 times more illnesses and 45 times hospitalizations than pasteurized milk. However, pasteurized milk has also been implicated in contamination outbreaks. Listeria monocytogenes is commonly found in contaminated pasteurized milk due to its ability to survive pasteurization. To maintain public safety, the population must be educated  about common milk-borne diseases, their potential hazards, and strategies to prevent contamination. Keeping the milk refrigerated between 2–8 degrees Celsius will minimize pathogen growth (Kapoor et al., 2023). 

Consumption of fresh produce exposes individuals to a higher risk of food-borne illnesses. Popular products that come labeled as “washed and ready to eat have been associated with contamination outbreaks. Common microbes found in contaminated produce are Escherichia coli, Salmonella, Listeria, Norovirus, and Hepatitis A virus. Standardization of food Handling protocols and education to business operators improves public safety in this regard (Machado-Moreira et al., 2019).

Every year, nearly 9 million people are affected by foodborne illnesses caused by contaminated food. Leafy green vegetables account for a significant portion of these cases. Research shows that certain microorganisms can survive and even grow on produce after it has been washed and packaged under strict safety standards. Household handling practices—such as storage conditions, temperature, and the length of time produce is kept—play a major role in determining microbial growth and the risk of foodborne illness. Studies indicate that the longer produce is stored, the higher the microbial load becomes. Notably, pathogenic strains like E. coli are capable of multiplying even under refrigeration (Uhlig et al., 2022 ).

In this experiment we start by culturing samples from two containers of milk stored in the refrigerator for 7 days, ne opened and one sealed since purchase. We also collected two lettuce samples, one before washing and one after washing. The goal was to compare microbial growth across these samples to evaluate how household food handling practices, such as washing and storage, influence food safety and whether these measures effectively reduce microbial contamination and the risk of foodborne illness.

We used aseptic techniques to collect and analyze microbial samples from milk and lettuce. Sterile swabs were used to transfer samples from each food item to pre-poured TSA agar plates, which were divided into labeled sections for comparison. The plates were then incubated inverted for 48–72 hours to allow microbial growth. After incubation, we observed the plates without removing the lids, counted the number of colony types and total colonies in each section, and recorded the results in a data table. Personal protective equipment (PPE) such as gloves, goggles, masks, and aprons, along with 10% bleach, was used throughout to maintain safety and prevent contamination.

Photos and graphic illustrations in this section with graphics in .jpg, .tif, or .gif format to minimize electronic file size.

Materials and Methods

Materials:

· Bottle of bleach

· Bottle of distilled water

· Camera

· Coffee cup

· Hand soap

· Isopropyl (rubbing) alcohol

· Large cooking pot

· Leaf lettuce-fresh, unwashed

· Oven mitt

· Roll of paper towels

· Small container of milk

· Source of tap water

· Stove or hotplate

· Apron

· Face mask with ear loops

· Pair of gloves

· Pair of safety goggles

· Permanent marker

· Petri dish, 90 mm

· Sterile swab, 2 per pack

· Test Tube rack, 6 x 21 mm

· Test tube clamp

· Tryptic soy agar (TSA), 18 mL tube

Methods

In this experiment, two samples of milk and two samples of lettuce were collected to analyze microbial growth. We used Sterile cotton swabs to collect the samples and employed aseptic techniques to prevent contamination. Two TSA agar plates were prepared and divided into labeled sections: “Milk Fresh” and “Milk Opened” on one plate, and “Lettuce Washed” and “Lettuce Unwashed” on the other. Samples from the unwashed lettuce were transferred onto the corresponding section of the agar plate, and the swabs were disposed of in undiluted bleach. The lettuce was then washed, dried, and swabbed again for the “Lettuce Washed” section. Similarly, an opened milk sample stored for seven days and a fresh unopened milk sample were swabbed and inoculated onto their respective sections of the agar plate. All plates were inverted and incubated at room temperature for 48 hours. After incubation, microbial growth was observed without removing the lids, counting both the number of colony types and total colonies for each section. Photos of the plates were taken, and all reusable and disposable materials were disinfected or disposed of using a 10% bleach solution to maintain aseptic conditions. Personal protective equipment (PPE), including gloves, goggles, masks, and aprons, was worn throughout the experiment. At the end, pictures were taken to document the plates for visual analysis and record-keeping.

Results

Summary of the results

· Fresh milk plate → few colonies, often sparse and uniform.

· 7-day open milk plate → many colonies, high diversity (rods, cocci, sometimes fungi), showing spoilage organisms have multiplied.

Unwashed lettuce

· High microbial load:

· Soil bacteria (Pseudomonas, Bacillus, Clostridium spores).

· Enteric bacteria (possible E. coli, Salmonella).

· Lactic acid bacteria and yeasts.

· Agar plate results:

· Dense growth, often too numerous to count (TNTC).

· Colonies vary widely in shape, color, and texture (smooth, rough, white, yellow, opaque, etc.).

· Possible presence of fungi (fluffy mold colonies).

🥬 Washed lettuce (rinsed in water)

· Reduced microbial load, but not sterile:

· Many surface bacteria are rinsed off, lowering colony counts.

· Some microbes remain because they stick tightly to leaf crevices or biofilms.

· Agar plate results:

· Fewer colonies than unwashed lettuce.

· Still shows a mix of bacteria and yeasts, but less diversity and density compared to unwashed.

🥬 Key Difference

· Unwashed lettuce → much higher microbial diversity and numbers.

· Washed lettuce → reduced colony counts, but washing alone does not eliminate all microbes.

Results

· Results section is written in paragraph form and is one or two pages long

· Do not offer any explanation for the results in this section

· Presents the results in text and graphic form (figures, tables, graphs)

· Describes the general trends seen in the data in narrative form (paragraphs).

· All figures and tables should be referenced in the narrative.

Do not redraw the graph in words; let it do the work for you. For example, Temperature had a pronounced effect on seedling growth rate (Figure

Discussion

· The discussion is the meat of the lab report.

· Tries to answer the question "Why?" Explains what was expected and what was found.

· Do the data support the original hypothesis? Why or why not?

· This section presents reasons for the results obtained in the experiment and references related studies.

· What trends were noticed; why did they occur?

· What is the theory or model behind the experiment and is it substantiated by your results?

· This section also includes potential sources of error. What recommendations might improve the procedure and results?

Consideration is given to:

· What is the connection between the experimental measurements taken and the final results and conclusions? How do your results relate to the real world?

· What were the results of observations and calculations?

· What trends were noticed?

· What is the theory or model behind the experiment?

· Do the experimental results substantiate or refute the theory? Why? Be sure to refer specifically to the results you obtained.

· Were the results consistent with your original predictions of outcomes or were you forced to revise your thinking?

· Did errors occur (for example, environmental changes or unplanned interference in the procedure)? If so, how did these errors affect the experiment?

· Did any errors occur due to the equipment used (for example, contamination due to a lack of aseptic technique)?

What recommendations might improve the procedures and results?

Conclusion

· Consists of a single paragraph.

· Restates the objective, the results, and important discussion findings; Does NOT introduce new material.

· Conclusion should be supported by at least 3 reasons and/or pieces of data obtained from the experiment.

Citations

Kapoor, Sunandini et al. “Milk-borne diseases through the lens of one health.”  Frontiers in microbiology vol. 14 1041051. 6 Apr. 2023, doi:10.3389/fmicb.2023.1041051

Machado-Moreira, Bernardino et al. “Microbial Contamination of Fresh Produce: What, Where, and How?.”  Comprehensive reviews in food science and food safety vol. 18,6 (2019): 1727-1750. doi:10.1111/1541-4337.12487

Uhlig, E et al. “The live bacterial load and microbiota composition of prepacked "ready-to-eat" leafy greens during household conditions, with special reference to E. coli.”  International journal of food microbiology vol. 377 (2022): 109786. doi:10.1016/j.ijfoodmicro.2022.109786