Chapter 13

What is the effect of ionizing radiation on microbes?

Ionizing radiation, such as gamma rays and X-rays, causes extensive DNA damage, leading to cell death.

What is sonication, and what is its mode of action?

Sonication involves exposure to ultrasonic waves that create cavitation, disrupting and lysing microbial cells.

Describe the pasteurization process and its effectiveness.

Pasteurization involves brief heat treatment to reduce harmful pathogens, generally not achieving complete sterilization.

What is the role of surgical scrubbing compared to regular handwashing?

Surgical scrubbing is more extensive and includes scrubbing from fingertips to beyond the elbows to ensure thorough decontamination.

What is autoclaving, and why is it considered the 'gold standard' for sterilization?

Autoclaving is a method that uses steam under pressure at 121°C for ≥ 20 minutes, effectively sterilizing most microbes, including endospores.

What are the four biosafety levels (BSL) of containment?

BSL-4 is for dangerous pathogens with no treatments; BSL-3 is for serious diseases; BSL-2 is for moderate risk microbes; BSL-1 is for nonpathogenic microbes.

What are the five factors that complicate the selection of an antimicrobial procedure?

The five factors are type of microbes, number of microbes, environmental conditions, risk of infection, and composition of the infected item.

What is the significance of the zone of inhibition in a disk diffusion assay?

The zone of inhibition indicates the effectiveness of an antimicrobial agent against a specific microbe, with larger zones reflecting greater efficacy.

What are the common uses of membrane filtration in laboratories?

Membrane filtration is used for removing bacteria from heat-sensitive solutions like vitamins and antibiotics.

What is the function of HEPA filters in air filtration?

HEPA filters remove microbes, endospores, and viruses from the air as it passes through the filter system.

How does lyophilization preserve food?

Lyophilization removes water through freeze-drying, creating a hypertonic environment that inhibits microbial growth.

What is the significance of the center console in cars regarding microbial contamination?

The center console harbors the most microbes (506 CFUs) due to its role as a common area for placing and spilling drinks.

Identify the two common methods of pasteurization and their specific temperatures.

High Temperature Short Time (HTST) heats milk to 72°C for 15 seconds; Ultra-High Temperature (UHT) heats it to higher temperatures for a shorter time.

What is the importance of handwashing in microbial control?

Handwashing is a simple yet effective method for reducing microbial load and preventing infections.

What is the impact of high temperature short time (HTST) pasteurization on food safety?

HTST pasteurization effectively reduces the number of harmful pathogens in food without achieving complete sterilization.

How does incineration control microbial populations?

Incineration destroys microbes by burning them, effectively eliminating biological materials.

What is the effect of cold storage on microbial cultures?

Cold storage at ultra-low temperatures can preserve microbial cultures and medical specimens for extended periods.

Define '-static' and '-cide' in the context of microbial control.

'-static' refers to methods that inhibit microbial growth, while '-cide' refers to methods that kill or inactivate microbes.

Explain the process and effectiveness of autoclaving.

Autoclaving denatures proteins and alters membranes, effectively killing most microbes, including endospores, under high pressure and temperature.

What is the role of cold temperatures in microbial growth control?

Cold temperatures inhibit microbial metabolism and slow growth, with refrigeration (4°C) and freezing (-20°C) used to delay food spoilage.

Explain the concept of the decimal reduction time (D-value).

The D-value is the time required to kill 90% of a microbial population under specific conditions.

How does the addition of solutes affect food preservation through desiccation?

The addition of solutes creates a hypertonic environment, drawing water out of microbial cells and inhibiting their growth.

What are the effects of boiling in microbial control?

Boiling at 100°C is an old method that kills many microbes but does not achieve complete sterilization.

What is the purpose of membrane filtration, and what size filter is typically used?

Membrane filtration uses filters with pore sizes of 0.2 μm or smaller to physically remove microbes from liquid solutions.

How does HEPA filtration work in controlling microbial growth?

HEPA filtration uses high-efficiency particulate air filters with 0.3 μm pore size to physically remove microbes from the air.

How does high-pressure processing contribute to food safety?

High-pressure processing kills bacteria, yeast, and viruses by denaturing proteins, maintaining food quality and extending shelf life.

How does UV radiation affect microbial DNA?

UV radiation causes the formation of thymine dimers in DNA, which can lead to lethal mutations in exposed microbes.

What is a disk diffusion assay?

A disk diffusion assay tests the effectiveness of chemical agents against specific microbes by measuring the zone of inhibition around antimicrobial discs.

What is the significance of using pressure cookers at home in relation to autoclaving?

Pressure cookers function similarly to autoclaves by raising the temperature of water above boiling, effectively killing endospores.

Define desiccation in microbial control.

Desiccation is the removal of water from microbes, which inhibits their growth and can be achieved through methods like lyophilization.

What is the purpose of gamma irradiation in food treatment?

Gamma irradiation is used to sterilize food and must be labeled with the irradiation symbol, known as the 'radura'.

What is the primary action of bactericides compared to bacteriostatic agents?

Bactericides kill bacteria, while bacteriostatic agents inhibit their growth without killing them.

What are the common uses of autoclaving in microbial control?

Autoclaving is used for sterilizing laboratory equipment and medical instruments by using steam under pressure.

What are the effects of desiccation on microbial viability?

Desiccation removes water essential for microbial metabolism, leading to reduced viability and growth.

What is the role of UV radiation in microbial control?

UV radiation causes DNA damage by forming thymine dimers, leading to mutations and potentially lethal effects in exposed microbes.

What is the importance of labeling gamma-irradiated foods?

Labeling indicates that the food has undergone irradiation treatment, ensuring transparency and safety for consumers.

How do environmental conditions affect antimicrobial procedures?

Environmental conditions such as temperature, pH, and presence of organic matter can influence the effectiveness of antimicrobial treatments.

What is the function of germicidal chemicals in microbial control?

Germicidal chemicals are designed to kill or inactivate microbes, reducing their populations significantly.

What is the significance of antimicrobial agents showing different effectiveness against various microbes?

Different microbes have varying susceptibilities to antimicrobial agents, which is crucial for selecting appropriate treatments.

What is the difference between bactericidal and bacteriostatic agents?

Bactericidal agents kill bacteria, while bacteriostatic agents inhibit their growth.

What is the significance of the disk diffusion assay in antimicrobial testing?

The disk diffusion assay evaluates the effectiveness of antimicrobial agents against specific microbial species.

What is the relationship between microbial death and time as shown in the microbial death curve?

The microbial death curve illustrates a logarithmic decrease in the number of live bacterial cells over time.

What is the significance of cold temperatures in microbial growth control?

Cold temperatures inhibit microbial metabolism, slowing growth and extending the shelf life of food.

What is the process of pasteurization and its primary goal?

Pasteurization involves brief heat treatment to reduce harmful pathogens in food without sterilizing it completely.

What does the CDC recommend for effective handwashing?

The CDC recommends a five-step handwashing process to effectively reduce microbial presence on hands.

What is the primary action of sonication in microbial control?

Sonication uses ultrasonic waves to create cavitation, leading to cell disruption and lysis.

What is the impact of boiling on microbial populations?

Boiling kills many vegetative cells and some viruses, but may not eliminate all endospores.

What is the primary purpose of surgical scrubbing?

Surgical scrubbing is intended to reduce microbial load on the hands and forearms prior to surgery.

What is the role of solutes in food preservation through desiccation?

Solutes create a hypertonic environment that draws water out of microbial cells, inhibiting their growth.

What factors influence the size of the zone of inhibition in antimicrobial testing?

Factors include the effectiveness of the antimicrobial, its concentration, molecular weight, and stability.

What does lyophilization involve in food preservation?

Lyophilization, or freeze-drying, removes water from food, preserving it by creating a hypertonic environment.

How does membrane filtration function in microbial control?

Membrane filtration physically removes microbes from liquids using filters with pore sizes typically of 0.2 μm or smaller.

How is the zone of inhibition measured in a disk diffusion assay?

The zone of inhibition is measured as the clear area around an antimicrobial disk on an agar plate, indicating the effectiveness of the antimicrobial.

What is the effect of ionizing radiation on microbial DNA?

Ionizing radiation causes extensive DNA damage, leading to cell death through breaks in the sugar-phosphate backbone and changes in nucleotide structure.

What is the primary goal of using high-temperature short-time (HTST) pasteurization?

HTST pasteurization aims to eliminate harmful pathogens while preserving the quality of food products.

What does the D-value represent in microbial control?

The D-value is the time required to kill 90% of a microbial population under a specific treatment.

What are the four biosafety levels and their corresponding descriptions?

BSL-1: Minimal risk; BSL-2: Moderate risk; BSL-3: Serious risk; BSL-4: High risk with no treatments available.

How does the concentration of an antimicrobial agent affect its efficacy?

Higher concentrations of antimicrobial agents generally increase their effectiveness against microbial populations.

How does incineration contribute to microbial control?

Incineration destroys microbes by burning them, effectively eliminating all forms of microbial life.

How does high-pressure processing affect microbial populations in food?

High-pressure processing kills bacteria, yeast, mold, parasites, and viruses by denaturing proteins, while maintaining food quality.

What is the importance of measuring the decimal reduction time (DRT)?

The DRT provides a quantitative measure of the effectiveness of a microbial control method over time.

What is the primary mode of action of HEPA filters?

HEPA filters physically remove microbes and particles from the air as it passes through the filter.