Free Essay: Effect of Refrigeration and Covering of Mayonnaise on the Growth of Bacteria

Abstract

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Growth is characteristic feature of life; this simply means the regulated and coordinated enlargement in biological mass over time. Bacterial growth involves division of one cell of the bacteria into two cells in a process known as binary fission. Specific conditions are required for the survival of bacteria. Most bacteria require environments that are moderate, suitable and assure optimum growth. The common conditions that need to be set include temperature, oxygen concentration, nutrients, salt concentration and pH. Different bacterial species have to be well examined to allow bacterial growth in an artificial lab condition. Optimum oxygen levels and aeration are necessary for bacteria growth as it acts as a primary electro acceptor in aerobic respiration processes. It is during these processes that oxygen is reduced to water (Koseki & Isobe, 2005).

Due to the need of bacteria to get oxygen and carbon dioxide from the atmosphere for their growth processes, we built an experiment with aim to invigilate two objectives. One of the objectives was to investigate the increase in microbial populations of mayonnaise due to lack of refrigeration and the other was to investigate if there would be more increase in microbial populations of mayonnaise if exposed to the atmosphere. The experiment was done in three different conditions, one of which was a control group. From the experiment we found out that the container with lid had a lot of colony forming units (166) though it was more dilute followed by the container without the lid (109) and finally the container that stayed in the refrigerator all through (64). But when it comes to the bacteria species, the container without the lid had the highest number of species (4) compared to the others followed by the container with the lid (2) and finally the control group had only one species. Thus we can conclude that bacteria growth is dependent on the state of being refrigerated or not and being covered or not (MacLeod, Smith & Gelinas, 1966).

Introduction

Bacteria are prokaryotic microorganisms that do not contain chlorophyll. They differ from eukaryotic organisms by not having nuclear membrane and cell organelles such as Golgi apparatus, endoplasmic reticulum, and mitochondria. They are unicellular and show no branching. Bacteria have a single circular chromosome.

Growth is characteristic feature of life; this simply means the regulated and coordinated enlargement in biological mass over time. Bacterial growth involves division of one cell of the bacteria into two cells in a process known as binary fission. Reproduction and bacterial growth are closely related.

Specific conditions are required for the survival of bacteria. As a human being, it is difficult to survive in a freezer, with no food or oxygen or sitting in stomach acid and so are the bacteria. Several parameters need to be set if growth of bacteria is to be realized. Most bacteria require environments that are moderate, suitable and assure optimum growth. The common conditions that need to be set include temperature, oxygen concentration, nutrients, salt concentration and pH. Different bacterial species have to be well examined to allow bacterial growth in an artificial lab condition (Laws, Pei & Bienfang, 2013).

Generally water is an essential factor that a lot of bacteria depend on in their environments for the survival, From search environments bacteria are able to absorb dissolved growth supporting factors and nutrients. The nutrients in search environments are usually in dissolved form in order to allow active and passive take up by the bacterial cell. Energy is another essential requirement for any bacteria to survive as no life can exist without it. Microorganisms like algae, diatoms, cycanobacteria require carbon dioxide in order to build more complex carbon molecules such as glucose with the presence of sunlight in a process called photosynthesis. These organisms are known as C-autotrophic because they require light with the supply of carbon dioxide in order to promote growth. Fungi, protists and bacteria are C-heterotrophs since they retrieve carbon and their macronutrients build up of cell material from organic nutrients.

Appropriate temperature should also be considered as different bacteria have different expectations of temperature in their environments for them to show maximum growth, for example enterobacteriaceae requires temperatures of between 20oc to 42oc for them to exhibit maximum growth. Most bacteria require a pH (concentration of free protons (H+) in a given medium) of around 7 (neutral pH) to exhibit optimum growth.

Concentration of nutritional resources is also a focal point in the growth of microbial bacteria. The study of bacterial growth kinetics by pioneer Jacques Monod demonstrated the relationship between bacterial growth and limiting nutrient concentrations. He demonstrated that bacterial growth is linearly dependent on initial concentration of the limiting nutrient. He also mathematically incorporated this relation in the exponential bacterial growth equation and was able to come up with a model similar to the Michaelis-Mention representation of enzyme kinetics for the relationship between concentration of the limiting nutrient and growth rate (2015).

Optimum oxygen levels and aeration are necessary for bacteria growth as it acts as a primary electro acceptor in aerobic respiration processes. It is during these processes that oxygen is reduced to water. Despite the ability of the cells to derive their oxygen from water and carbon dioxide, molecular oxygen in the air or dissolved in water is mostly the one used by cells take up via diffusible processes. Bacteria that need oxygen for survival are known as aerobic bacteria while those that do not require oxygen are known as anaerobic bacteria. Aerobic bacteria also may be facultative anaerobes (are aerobic but can do without oxygen) and obligate aerobes (can only grow in the presence of oxygen). Obligate anaerobes can die with exposure to oxygen while microaerophilic bacteria grow best only when there is low presence of oxygen tension (Willey et al., 2008).

Anaerobic bacteria use sulphates and nitrates as electron acceptor in the process of respiration and the process used in the anaerobic metabolism is fermentation (process by which glucose is broken down into simpler compounds by enzyme action in the absence of oxygen). Every bacterium needs some amount of carbon dioxide for optimum growth. It can either be obtained from cellular metabolism of the bacterial cell or from the atmosphere. Bacteria like Brucella abortus require more carbon dioxide for maximum growth and these are known as capnophilic (Koseki & Isobe, 2005).

A recent paper cited that mayonnaise has caused about 7% of the reported food poisoning in Brazil. Canned and bottled foods have a longer shelf life because of they are sterilized under high temperatures after packing. When canned foods are opened then their shelf life reduces.

Bacterial growth is exponential and under optimal conditions, the bacteria like E.coli can double in 20 minutes while Staph aureus can double in 30 minutes. So in two hours staph aureus has grown to 16 times while E.coli has grown 64 times thus if food is left over for longer time then there would enough contamination to make one ill (Laws, Pei & Bienfang, 2013).

Due to the need of bacteria to get oxygen and carbon dioxide from the atmosphere for their growth processes, we built an experiment with aim to invigilate two objectives. One of the objectives was to investigate the increase in microbial populations of mayonnaise due to lack of refrigeration and the other was to investigate if there would be more increase in microbial populations of mayonnaise if exposed to the atmosphere. To easily investigate our set objectives, we hypothesized that the microbial populations of the mayonnaise would increase from lack of refrigeration and that it would increase even further when exposed to open air given that temperature and time without refrigeration will remain constant (Willey et al., 2008).

Several reasons for our hypothesis were that we had the knowledge that microbial population growth could not be supported by extreme cold conditions like those exhibited in the refrigerator. Also we knew that since oxygen is an essential factor in acting as a primary electro acceptor in the respiration processes of some microorganisms, it would increase microbial population growth rate by far. We thought that keeping the temperature and time of being refrigerated at a constant level would not interrupt our decision since it would only be concentrated on the state of being covered or not covered and the state of being refrigerated or not.

In this experiment, the group that acted as a control (a group of the experiment that does not receive any kind of treatment and is always used as a benchmark for which other test results are measured against) was the mayonnaise in the refrigerator. The constant factors in the experiment included; temperature in the refrigerator remained unaltered and also the temperature in the room was allowed to remain constant. Other constant factors were: mayonnaise came from the same jar; the time that the mayonnaise was left unrefrigerated was the same and sample sizes of mayonnaise were measured. Our experimental group (group of any experiment that receives the treatments being tested, one treatment is tested at a time and the group is compared to the control group) was the one that was tested by changing the independent variable(s) for our case the refrigeration and cover or the lid of the jar. We made the group larger so as to arrive at definitive results. Our independent variables (variables whose variation does not depend on that of the other) in the entire experiment were the lid, the cover or the state of being covered and uncovered and the state of being refrigerated or not. From this simple design of our experiment we anticipated to see microbial growth first displayed from the lack of refrigeration as well as more increased growth by being exposed to the open air. The dependent variable (variable whose variation depends on that of the other variables) was the final state of the mayonnaise or the microbial population that it contained at the end of the experiment. We had stated that the microbial population of the mayo was dependent on the state of being covered or not covered and the state of being refrigerated or not (MacLeod, Smith & Gelinas, 1966).

Procedure used:

Two samples that contained mayonnaise from a jar in the fridge were taken and then placed into plastic storage containers. A jar was left in the fridge as the control group (a group of the experiment that does not receive any kind of treatment and is always used as a benchmark for which other test results are measured against). We covered one of the containers with a lid and the other container was left uncovered. Both the two containers one covered and the other uncovered were left outside of the patio for around three hours. There was a little bit of wind blowing outside and the temperature was about 70 degrees. After spending the three hours outside, the uncovered container was then covered with a lid and they were both placed back in the fridge together with the control group as they awaited preparation to be enumerated. We decided to use serial dilution (is a step by step dilution of a substance in solution and most usually the dilution factor at every step is constant thus forming a geometric progression of concentration in a logarithmic fashion) make pour plates using sterile technique (procedure where by cultures are manipulated without infecting the worker or contaminating the lab environment or the cultures themselves)....