the microbial growth control

A microorganism, especially a bacterium that causes disease, is referred to as a microbe. The term “microbial growth regulation” applies to the process of inhibiting or inhibiting and blocking the growth of these microorganisms. Controlling microbial development is critical in the medical sector, pharmaceutical and biotechnology sectors, university research, agriculture, and food manufacturing. There are two types of microbial growth management techniques: physical methods and chemical methods. Heating, autoclaving, filtration, low-temperature treatment, desiccation, adjusting Osmotic Pressure, and the use of radiation are all physical processes. The chemical methods include the use of disinfectants like phenols, alcohols, halogens heavy metals aldehydes, and pyroxygens. Agents which kill cells are called cidal agents; agents which inhibit the growth of cells (without killing them) are referred to as static agents (Davis, 2010). Thus, the term bactericidal refers to killing bacteria, and bacteriostatic refers to inhibiting the growth of bacterial cells. A bactericide kills bacteria, a fungicide kills fungi, and so on.
Control by Heat and UV Light
Heat is the most widely used agent for reducing the number of bacteria in a particular environment. The effect of temperature often reflects the normal habitat of the organisms in nature. Bacterial ecologists categorize the temperature, requirements of bacteria as follows:
Ultraviolet light (UV) is electromagnetic radiation that has a wavelength from 100 to 300 nm. UV light is antimicrobial because it damages DNA molecules and the genetic information (Harrison, 2011). When high dosages of UV light are absorbed, damage to the DNA is severe enough to kill the cell.
Per group of 4 students:
Broth culture of each of the following bacteria:
Serratiamarcescens, Bacillus subtilis, Escherichia coli
5 –Trypticase Soy Agar (TSA)plates, 8 –Trypticase Soy Broth (TSB) tubes , Sterile swabs , Water baths at indicated temperatures, Wire Inoculating loop, Bunsen burner, Striker
Effect of temperature on microbial growth
Serratia marcescens
Bacillus subtilis
Take 3 TSA plates and draw a line across the diameter of the plate and label eachside indicating the bacteria to be inoculated. Each plate should have a name and a label showing its lab time and temperature.
Incubate plates containing after making a zig-zag streak of the organisms on each plate in a 35 °C incubator, at room temperature and in a refrigerator at ~10°C.
Indicate growth at the different incubation temperatures while making note of the morphology of the colony. Characteristics to consider in colony morphology include size, shape, color, amount of growth and the colony form, margin and elevation.
Control by UV Light
Escherichia coli
Bacillus subtilis
Take 2 TSA plates. Inoculate each plate with a different organism and label appropriately. Draw a line along the diameter of each plate and label the various sides as plate control and plate exposed to UV light.
Inoculate each plate with a sterile swab. Plate organisms in three zig-zag patterns each pattern at a 45◦ angle from the other as shown below.

Expose the half of each plate to UV lighting while covering the plate control for 5 minutes. Incubate for 48 hours at 35◦C.
Indicate presence of growth by assessing both the control side of the plate and that exposed to UV lighting. Which bacteria showed growth in UV lighting? What might be the reason for this?
Control by Heat
Aim: study and examine the use of temperature as a method of microbial growth control. Determine the Thermal Death Time and Thermal Death Point.
Thermal Death Point: Lowest temperature needed to kill of all bacteria present in 10 minutes.
Thermal Death Time: Minimal length of time inwhich all bacteria will be killed at a given temperature (Witter, 2012)
Escherichia coli
Bacillus subtilis
Each student to take 2 Trypticase Soy Broth (TSB) tubes
Label your tube indicating the temperature, time, start time, microorganism and name
Make sure water baths at temperatures of 400C, 600C, 800C and 1000C are available
Inoculate each tube with the appropriate organism and expose each tube to heat for varying durations as indicated below while vortexing the tubes every 10 minutes.
10 minutes
20 minutes
30 minutes
40 minutes
Each group will work on different tubes at varying temperatures and times as indicated in the table below
Team 1 Team 2 Team 3 Team 4 Team 5 Team 6 40°C for 10 minutes
55°C for 40 minutes
80°C for 30 minutes
100°C for 20 minutes 40°C for 20 minutes
55°C for 30 minutes
80°C for 40 minutes
100°C for 10 minutes 40°C for 30 minutes
55°C for 40 minutes
80°C for 20 minutes
100°C for 10 minutes 40°C for 40 minutes
55°C for 20 minutes
80°C for 10 minutes
100°C for 30 minutes 40°C for 30 minutes
55°C for 20 minutes
80°C for 10 minutes
100°C for 40 minutes 40°C for 40 minutes
55°C for 10 minutes
80°C for 30 minutes
100°C for 20 minutes
Each tube should be assessed for growth, lack of growth and recorded appropriately.
Determine thermal time of death for each temperature
Determine thermal death point.
Davis, B. “Microorganisms.” Microorganisms vs. Temperature. N.p., 5 Apr. 2008. Web. 27 Mar. 2010.
Harrison, P. G. (2011). Control of microbial growth and of amphipod grazing by water-soluble compounds from leaves of Zostera marina. Marine Biology, 67(2), 225-230.
Witter, L. D. (2012). Psychrophilic bacteria—a review. Journal of Dairy Science, 44(6), 983-1015.

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