Question

Which of the following microbial control methods does not actually kill microbes or inhibit their growth but instead removes them physically from samples? a. filtration b. desiccation c. lyophilization d. nonionizing radiation

Short answer

The method that removes microbes physically without killing or inhibiting their growth is a. filtration.

Step-by-step solution

Understanding the Question

First, identify what each of the listed microbial control methods does. Filtration involves straining microbes from a solution or air. Desiccation is the process of drying out, which can kill or inhibit microbial growth. Lyophilization, or freeze-drying, preserves microbes by removing water and can inhibit their growth. Nonionizing radiation, such as ultraviolet light, can damage microbial DNA, thus killing or inhibiting microbial growth.

Identifying the Method of Physical Removal

Next, analyze which of the methods physically removes microbes without killing or inhibiting their growth. Filtration only removes microbes but does not kill them or stop their growth. Desiccation, lyophilization, and nonionizing radiation all work to either kill microbes or inhibit their growth.

Selecting the Correct Answer

Based on the analysis, the correct answer is the method that physically removes microbes without affecting their viability. Therefore, the correct answer is 'a. filtration' because it is the only method listed that physically removes microbes without killing or inhibiting their growth.

Key concepts

Filtration

Filtration is a method of microbial control that works by removing microorganisms from liquids or gases using physical barriers. This method can be particularly effective when it's necessary to sterilize substances that would be damaged by heat, such as certain pharmaceutical products, serums, and culture media.

There are different types of filters, including membrane filters and HEPA (High-Efficiency Particulate Air) filters. Membrane filters have pores that are small enough to trap bacteria, viruses, and even large proteins as liquids pass through. HEPA filters are used to clean the air of particulate contaminants, including microorganisms, in environments like hospitals and biological laboratories.

Filtration does not kill microbes but simply removes them, making it the correct answer to the textbook exercise question as it's the only method amongst the options that doesn't harm the microorganisms in any way but merely separates them from the sample.

Desiccation

Desiccation, or drying out, is a method of microbial control that involves removing water from microbes, which can result in the inhibition of growth or death of the organism. Water is essential for the metabolic processes of microbes; without it, many cannot reproduce or sustain biological functions.

While some more resilient microorganisms can withstand desiccation and enter a dormant state, many cannot survive extended periods of dryness. Desiccation has been used traditionally in food preservation, such as in the curing of meats or the drying of fruits, where the lack of moisture helps to prevent spoilage caused by microbial growth.

Lyophilization

Lyophilization, commonly known as freeze-drying, is a stabilization technique often used for the preservation of microbes, pharmaceuticals, and foods. During the lyophilization process, the material is first frozen and then subjected to a vacuum, which allows the frozen water in the material to sublimate directly from ice to vapor.

This method effectively preserves the structure and material integrity, including any microbes present, by removing water without causing heat damage. Although the microbes are not killed, their growth is inhibited due to the lack of water. This method is particularly useful in preserving microbial cultures for long-term storage, allowing them to be rehydrated and revived for later use.

Nonionizing Radiation

Nonionizing radiation refers to a range of wavelengths on the electromagnetic spectrum that do not have enough energy to ionize atoms but can still interact with biological material in a harmful way. Ultraviolet (UV) light, a common type of nonionizing radiation, is used in microbial control for its ability to damage microbial DNA.

Exposure to UV light can lead to the formation of thymine dimers in DNA molecules, which can cause mutations and ultimately cell death. This form of radiation is used for disinfection in various settings, including water treatment facilities and air purification systems. It's worth noting that while nonionizing radiation does not penetrate deeply, it's effective at sterilizing surfaces and transparent fluids exposed to the UV source.