Lab 2A_ Sterilization and Disinfection

Answers for Lab 2 Sterilization and disinfection with grading rubrics (10 points total) 1. Review Chapter 6 slides and animation for bacterial growth curve. Q1.1. List the 4 phases of bacterial growth. - The four phases of bacterial growth are the Lag phase, Logarithmic phase, Stationary phase, and Death phase. Q1. 2. What is the reason for bacterial death in the cell culture? Will bacteria spontaneously die in human infection? - A combination of elements relating to nutrition availability, environmental conditions, waste product accumulation, and other stressors can result in bacterial death in a cell culture. The interplay of numerous variables, including the host's immune response, the characteristics of the bacteria, and the effectiveness of medical treatments, determines whether bacteria continue to grow or die within the human body during an infection. Bacteria can survive and adapt in some circumstances, resulting in chronic or recurrent infections, even while the immune system and medical therapies work to prevent or manage bacterial infections. 2. Review slides for Chapter 7 and the rate of bacterial death Q2.1. How does the rate of bacterial death change after treatment with antimicrobial chemicals? - Due to the direct bactericidal or bacteriostatic effects of antimicrobial substances, the rate of bacterial death increases following treatment. The type of antimicrobial agent, the type of bacteria, the quantity of the chemical, and the length of exposure are only a few examples of the variables that affect the effectiveness of treatment. Q2.2. How will the time of the treatment affect the number of dead bacteria? - The number of dead bacteria directly correlates with the duration of the antimicrobial treatment. A greater number of bacterial deaths and a more significant decline in the bacterial population are often the results of longer treatment times. However, depending on variables like the type of antimicrobial agent, bacterial sensitivity, and the existence of biofilms or resistant strains, the precise amount of time needed for effective treatment can change. Q2.3. Why do you have to treat 2,000,000 bacteria with 70% alcohol longer than 200,000 bacteria? - The size of the bacterial population that needs to be treated determines how long the disinfection process will take when using 70% alcohol. Smaller populations can be treated in a shorter amount of time, whereas larger populations need longer treatment times to achieve complete coverage, exposure, and effective bacteria inactivation.

Q2.4. What is the difference between sterilization and disinfection? - The main difference between sterilization and disinfection is in their objectives and level of microbial control; sterilization aims to completely eliminate all germs and achieves absolute microbial purity. Disinfection, on the other hand, seeks to remove certain pathogenic microorganisms but does not always do so. 3. Estimation of bacterial number by indirect method. Review chapter 6 lecture. Q3.1. How do you detect the growth of microorganisms in the culture media? - For tracking their growth and evaluating the efficacy of microbial cultivation, it is important to detect the growth of microorganisms in culture media. Microbial growth in culture media can be discovered using a number of techniques: Measurement of turbidity, colony growth on agar plates, gas production, pH indicator dyes, measurement of biomass, measurement of respiration and oxygen consumption, metabolic assays, and molecular methods. Q3.2. What is turbidity? - Turbidity is a term used to describe the cloudiness or opaqueness of a liquid brought on by the light being scattered by particles suspended in the liquid, such as microbial cells. It is frequently used in microbiological research and commercial processes as a useful tool for inferring the growth and density of bacteria in liquid cultures. Q3.3. How to measure turbidity? - A spectrophotometer or turbidimeter is a common scientific tool used to measure turbidity. These tools calculate the optical density (OD) or absorbance of a liquid sample by measuring the quantity of light scattered by the sample. Q3,4. In a scale of 0-4 give a rank to the level of turbidity in each tube on Figure 1 and explain why turbidity is different. - Tube 1: Rank 0 - Tube 2: Rank 1 - Tube 3: Rank 2 - Tube 4: Rank 4 A microbial culture's turbidity may alter for a number of reasons, and these fluctuations are frequently a sign of various growth phases, the presence of certain bacteria, or adjustments to the culture environment.

70% Alcohol (Tube #2): - Initial Count (Control Tube #6): 450 CFUs - Final Count (Treatment Tube #2): 245 CFUs Percent Reduction=(450−245450)×100% 3% Hydrogen Peroxide (Tube #3): - Initial Count (Control Tube #6): 450 CFUs - Final Count (Treatment Tube #3): 240 CFUs Percent Reduction=(450−240450)×100% Answer: Using Plates counts: 70% alcohol - 245 3% hydrogen peroxide - 240 Oral rinse – 265 Lysol – 250 Boil - 0 Q5.3. Which method of bacterial number estimation is more precise? - Direct count techniques, such as microscopic counts and flow cytometry, are often more accurate than indirect techniques, such as turbidity measures, if precision is the main consideration. Q5.4.Which of the treatments is the most effective method and which one is the least effective method for disinfection of medical instruments contaminated with S. aureus? - According to the data presented, boiling (Tube #1) appears to be the most efficient technique for disinfecting medical equipment infected with S. aureus because it completely eliminates the bacterium. Table 1 S. aureus Tube # Treatment Growth In The Tube Plate Counts 1 Boil 0 0 2 70% Alcohol 2 245 3 3% Hydrogen peroxide 2 240 4 Oral rinse 2 265 5 Lysol 2 250 6 Non-treated control 4 450