Bacterial Quantification by Culture

SCI/250 v5

Bacterial Quantification by Culture Lab Reporting Worksheet TITLE: Microbiology What was the title of the lab you completed?

Bacterial Quantification by Culture PROBLEM: What was the problem you were trying to resolve in the Lab? To determine the impact of serial dilutions on bacterial colonies HYPOTHESIS: What information from the textbook and classroom is relevant for the problem you were trying to resolve in the lab? Identify the concepts and explain how they are related to the lab problem.

Serial dilution is a systematic approach to determine the impact of a certain compound of bacterial growth. This process involves systematic reduction in the concentration of an antibacterial solution. The fixed volume of the liquid diluent is successively re-suspended to facilitate the logarithmic decrease in the quantity of the sample organism (Goldman & Green, 2021). At high concentrations, the bacterial growth agent facilitates bacterial growth whereas at low concentration the agent loses its effectiveness in supporting bacterial growth.

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Bacterial Quantification by Culture Lab Reporting Worksheet SCI/250 v5 Page 2 of 5 During the lab, what information from the THEORY section provided additional background information about the problem? (To review the theory section, launch the Lab and click the “Theory” tab on the top of the data pad). Identify the concepts and explain how they are related to the lab problem.

Serial dilution process is applied in microbiology to estimate the concentration of bacterial organisms in a sample.

This process helps obtain incubated plates containing colonies that are easier to count.

Most scientific experimentation involves examining variables and their relationships. A variable is a construct that can be changed and studied. Examples of variables are a condition or measurable quantity. What are the variables you examined in the lab? Which one were you controlling and changing? Which one were you observing was impacted by your change?

The dependent variable in this experiment was bacterial growth.

The independent variable was the nutrient concentration. The concentration of nutrients was controlled to influence bacterial growth

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Bacterial Quantification by Culture Lab Reporting Worksheet SCI/250 v5 Page 3 of 5

Developing a hypothesis requires understanding relevant background knowledge. Now that you have described relevant background information, it is time to develop a hypothesis.

Hypothesis 1: The number of colonies will decrease with each dilution Hypothesis 2: The first dilution will have the largest number of bacteria while the last dilution will have the least number of bacteria METHOD: You have already, identified the variables that you studied in the lab in the previous section. Now, take some time to fully define and describe what each variable is and how it was changed throughout the lab.

Serial dilutions serve as the independent variables in this experiment whereas bacteria colonies are the dependent variables. The serial dilutions influenced the concentration of the nutrient broth thus affecting the number of bacterial colonies.

In 3-5 sentences summarize what you did during the lab not including your process of logging into the system.

This section would be much more robust for a non-virtual lab. For this virtual lab, a short, high-level summary will suffice.

The first step was to gather the relevant materials including the nutrient broth, agar plates, and bacterial broth culture. Six tubes containing the liquid broth were labelled 1A, 1B, 1C, 1D, 1E, and 1F. Serial dilutions were prepared with the bacterial culture. Three nutrient agar plates were labelled 1D, 1E, and 1F were prepared and bacterial cultures spread on each using sterile spreaders. The plates were then incubated for 24 hours at 370C. The colonies on the agar plates were counted.

Describe some of the observations you made. What numbers did you write down or keep track of? What did each of your senses observe during the lab process? What did you see (ex: changes in colors, movement, shapes, sizes, patterns)? What did you hear (ex: sounds from reactions, collisions, error messages)? What did you lab character touch? Did you notice anything that seemed unexpected? Did you notice anything that you did expect to observe?

Bacterial growth was easily identifiable in the agar dishes. The surface of the agar turned white indicating bacterial growth.

Which parts of the lab required you to think more than others and required more time? Which parts were simple and completed easily?

Serial dilution was the most challenging part of the experiment. This step required concentration to eliminate inaccuracies which contribute to less precise dispensing and inaccurate results. Streaking is the easiest part of the experiment. It involves spreading bacterial culture on agar dishes and incubating at 370C. DATA & RESULTS: Many lessons learned because of scientific experiment come from the reporting and analysis of data. This part of scientific reporting requires detailed descriptions of technical information and quantities as well as high-level synthesis of information. High-level synthesis requires a mastery of foundational content in the related scientific field and a complimentary mastery in some field of quantitative and/or qualitative analysis.

For this report, let’s focus on big picture patterns. What relationships did you notice between the variables you examined? When you changed the variable(s), how did the other(s) change?

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Bacterial Quantification by Culture Lab Reporting Worksheet SCI/250 v5 Page 4 of 5

The number of colonies in dilution D, E, and F were 376, 23 and 4 respectively. The agar plates were subdivided into equal sections to facilitate counting. A high dilution contributed to a few bacterial colonies while a lower dilution led to largest number of bacterial colonies Did you notice any patterns in your data? Any patterns between the variables?

The experiment generated unique patterns between variables. . In serial dilution, the highest dilutions have more accurate results than least dilutions. These findings become inaccurate if errors occur during dilution.

DISCUSSION: The discussion section is used to explain why things might have happened the way that they did in your experiment. Here, scientists describe any potential anomalies or mistakes and why they think they may have occurred. During your lab, what happened that might have impacted the accuracy of your data? Did the simulation alert you that an error was occurring? If so, how did you resolve it?

The least number of bacterial colonies were observed in the more dilute original culture. Many streaks also reduced the number of bacterial colonies. However, the numbers of bacteria colonies were not consistent with the dilution.

This problem might have occurred due to air bubbles in the pipette during dilution. Air bubbles decreased the quantity of pipetted solution.

CONCLUSION: The conclusion section of a lab report describes how the learnings from the lab experimentation fit in to prior scientific knowledge. This is done by comparing new information to previously known information that was identified in the section of your report that discusses background information. Review the hypothesis section of your report from above and describe how the results of your lab compare to the background information that you discussed before.

The results confirmed the hypothesis indicating that the number of bacterial cells decreased significantly with each dilution. The experiment shows that serial dilution of nutrient broth affects bacterial colony formation.

Once scientists have identified how the new knowledge fits into the old knowledge, they discuss the implications of the new information for moving forward. In this class, the purpose of study is to learn some foundational science ideas represented by the course student learning outcomes. Review the course student learning outcome aligned to this lab in the assignment directions in Blackboard. How is the information from this lab related to the course student learning outcome? What knowledge has the lab supported you with learning that is related to this course student learning outcome?

This experiment increases knowledge on colony streaking skills, serial dilution, and ascetic technique.

Following scientific experimentation, scientists usually come up with new questions that result from what they learned. These new questions often end up leading to new experiments in the future. What additional scientific things do you wonder about after completing and writing about your lab experience?

The main question regarding serial dilution as a bacterial quantification method is whether this procedure could be used to identify or separate different bacteria or pathogenic organisms

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Bacterial Quantification by Culture Lab Reporting Worksheet SCI/250 v5 Page 5 of 5 References Goldman, E., & Green, L. H. (2021). Practical handbook of microbiology. CRC Press,

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