Research Paper on Microbiology

Introduction/Background Information

The growth of microorganisms differs widely with various factors such as temperature, Ph, water activity, and redox potential. However, the growth of microorganisms when subjected to very high temperatures or extremely moderate temperatures vary. Control of bacteria is essential in ensuring effective food preservation and also prevent disease-causing organisms ("Food Microbiology," 2014). Microbial control growth is done through two main ways which involve either killing of microorganisms or inhibiting the growth of microorganisms. Controlling the growth bacteria consists of the use of physical or chemical methods such as the use of bactericides or the sterilization process (Yoshida & Kobayashi, 2013). Sterilization involves complete distraction of the bacteria by application of heat and includes various methods such as incineration, use of dry heat, boiling, and autoclaving which consists of the use of steam under pressure.

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On the other hand, inhibiting the growth of bacteria involves various methods such as reduction of pH-reducing the water activity through dehydration and additional of solutes. Nonetheless, the modification of redox potential through the addition of additives such as nitrates that alter the redox potential and lastly through the use of temperatures by either increasing or reducing temperature depending on the type of bacteria (Black & Black, 2014). The organisms used are E. coli and B. subtilis since it is easy and cheap to grow and also the E. coli acts as an indicator organism, therefore, shows the presence of faecal coliform in a contaminated faecal matter to indicate the presence of the disease-causing organism. Research demonstrates that ultra-violet rays' radiation also affects microorganisms effectively since, on submission to the ultra-violet ray radiation, the E. coli attains a 100% mortality. Furthermore, the chances of survival of the E. coli decreases with the increase in radiation at a specific wavelength. Statistics indicate that the two bacterial species were exposed to auxins to determine the possible effect when it comes to tolerance also bacterial resistance to the Uv radiation. When the two species become exposed to UV rays and have been preheated with auxins, they tend to survive, unlike the untreated ones. Therefore, according to this previous research, auxins tend to enhance or reduce the tolerance of stressors such as heat or ultraviolet rays.

Purpose of the Study

The scope of this investigation is to circumscribe the thermal death time of the two species E. coli and B. subtilis, the control of bacterial using heat and how ultraviolet rays affect bacteria. Heat is the basis of the experimental as a different bacterial organism are exposed to heat factors and the reaction estimated.

Hypothesis

Moreover, it is hypothesized that the thermal death time of the two species is different and also an increase in the level of radiation dosage leads to the direct death of bacteria. The bacterial reaction to heat is a predetermined idea that bears the weight of the experiment.

Procedure

The initial bacterial count was determined through the preparation of dilutions of different labelled test tubes where the 1ml bacterial culture was transferred to a plate and became the undiluted sample. For the dilution preparation of the first test tube, 1ml from the broth culture is moved into the 9ml dilution bank and mixed effectively. For the second test tube dilution, 1ml from the dilution in the first test tube was obtained and combined with the fresh 9ml dilution blank. The procedure was therefore repeated using a fresh sterile pipette tip up to the last test tube. Finally, 1ml from each dilution prepared was obtained and transferred to a petri dish where agar was poured into each petri dish, mixed thoroughly and allowed to set. The bacterial culture was then immersed in a water bath at 80 degrees Celsius. After a minute, the 1ml sample was obtained and transferred into a petri dish. Another 1ml from the specimen was also collected and moved to a 9ml dilution to achieve a ten dilution and a series of dilutions made up to 10. The agar was then poured into the plates, mixed and allowed to set until the next session for observation.

Subsequently, a sterile cotton swab was immersed in broth culture S. marcescens to investigate the bactericidal effect of ultraviolet radiations. The agar was further inoculated wholly and evenly using a swab and one plate labelled to act as a control plate which was not exposed to UV light. The remaining four plates were exposed to UV light where the lids were replaced with square piece cardboard in which a design of the period of exposure was cut. Furthermore, the plates which were covered by cardboard lids were subjected to UV lamp for different periods of time. After the exhibition, the plates were removed from the lamp and tops replaced. One dish was exposed with its cover for 3 minutes and all plates incubated for 48 hours at room temperature.

Representation of Data

Table 1. Effects of heating at 800c on viable count (c.f.u. /ml)

Table 1 shows the effect of heat on E. coli and B. subtilis at 800C. At 5 minutes, the E. coli species die at a faster rate than the B. subtilis since the B. subtilis has high heat resistance than the E. coli.

Results

In the control of bacteria using heat experiment, the thermal effect on the organisms are different. The B. subtilis has more heat resistance than the E. coli furthermore, the E. coli thermal death time is at 5 minutes, but the B. subtilis can still survive. However, the difference in heat resistance is due to the formation of endospores by the B. subtilis which requires a temperature of 1000C for 20 minutes to be complete. The E. coli does not form endospores therefore only needs a temperature of 800C for 10 minutes.

In the bactericidal effect of ultraviolet rays experiment at one minute, the ultraviolet rays kill the colonies, but still, there is growth at the edge, in 30 seconds. Although not all colonies are exterminated after exposure to the ultraviolet, in three minutes, the colonies are killed. Consequently, after three minutes the plate with the lid starts the growth of colonies since the ultraviolet radiation is not intense enough to pass through the cover, therefore, the area that was exposed to the ultraviolet with the plastic lid had growth. When the extension on the control plate and that of the plate exposed with the top, there was growth on them at 3-minute exposure to the ultraviolet rays.

In previous studies, other methods of technology have been used to control microbial growth. Such as irradiation which involves radappertization, radicidation, and radurization. Irradiation occurs where microorganisms are destroyed in two ways directly through the use of rising in temperature and the one that does not involve temperature increase (Cain, 2012). The direct mode of action requires ejection of an electron from the DNA structure. Indirectly, it leads to the formation of free radicals which further react with the DNA ("International Journal of Food Microbiology," 2015). Radappertization involves the application of a dose of ionizing radiation to decrease the number and movement of viable microorganisms to such a degree that is not detectable. Radicidation is a form of food irradiation where the dose of ionization is applied to the food reduce the number of viable specific non-spore forming pathogenic to structures that are not traceable while radurization involves application using the dose of ionizing radiation by reducing the presence of spoilage microorganisms through enhancement of quality for future developments.

Conclusion

To sum up, the hypothesis was correct, and this investigation shows that the thermal effect of the species E. coli and B. subtilis are different and the increase in the level of radiation dosage leads to the direct death of bacteria.

References

Black, J., & Black, L. (2014). Microbiology. New York: Wiley.

Cain, R. (2012). Food, Inglorious Food: Food Safety, Food Libel, and Free Speech. American Business Law Journal, 49(2), 275-324. Doi: 10.1111/j.1744-1714.2012. 01133.x Doi: 10.1016/s0740-0020(14)00320-7

Food Microbiology. (2014). Food Microbiology, 40, I-II. doi: 10.1016/s0740-0020(14)00025-2

International Journal of Food Microbiology. (2015). Food Microbiology, 47, I.

Kolter, R., & Chimileski, S. (2018). The End of Microbiology. Environmental Microbiology.

Yoshida, R., & Kobayashi, H. (2013). Adverse Events with Low Temperature Hydrogen Peroxide Gas Plasma Sterilisation Reported by Certified Sterilisation Service Technicians and Certified Sterilisation Specialists in Japan. Iryou Kikigaku (The Japanese Journal of Medical Instrumentation), 83(1), 28-33. Doi: 10.4286/jjmi.83.28.