Microbiology with Lab: A Fundamental Approach (D311)

Correct Answer

A. Inoculum

Explanation

In microbiology, an inoculum refers to the sample of microorganisms that is introduced into a culture medium to initiate growth. It is the starting point for cultivating microorganisms, typically a small amount of bacteria, fungi, or viruses, which will multiply and form colonies or cultures over time.

Why other options are wrong

B. Culture

A culture refers to the microorganisms that are grown from an inoculum. It is the result of introducing the inoculum into the culture medium, not the sample itself.

C. Specimen

A specimen refers to the sample taken from an organism or environment for examination or testing. It may or may not be used as an inoculum in microbiological procedures.

D. Colony

A colony is a visible cluster of microorganisms growing on a solid medium, often originating from a single cell. It is the result of microbial growth from an inoculum, not the inoculum itself.

Correct Answer

A. Inoculating loop and incinerator

Explanation

The inoculating loop and incinerator are key tools used to maintain asepsis in a microbiology lab. The inoculating loop is used for transferring microorganisms without contaminating the sample, and the incinerator (or Bunsen burner) is used to sterilize the loop before and after use to avoid cross-contamination. These tools help to ensure that the lab environment remains free of unwanted microorganisms, preventing contamination of cultures.

Why other options are wrong

B. Petri dish and microscope

Petri dishes and microscopes are essential for culturing and analyzing microorganisms, but they are not directly involved in maintaining asepsis. They are used in the observation and growth of microbial samples, not in preventing contamination.

C. Pipette and centrifuge

Pipettes and centrifuges are used for transferring liquids and separating components, respectively. While they are useful in microbiological procedures, they do not specifically serve to maintain asepsis during routine microbial culture handling.

D. Autoclave and incubator

Autoclaves and incubators are critical for sterilization and growing microbial cultures, respectively. However, while the autoclave is used for sterilization (maintaining asepsis in the lab), the incubator is used for growing cultures rather than directly maintaining asepsis during procedures.

Correct Answer

B. To reduce the refraction of light

Explanation

Immersion oil is used with the 100X objective lens to reduce the refraction of light as it passes from the specimen to the lens. Air between the slide and the objective lens causes light to bend, leading to a loss of resolution and clarity. Immersion oil has a similar refractive index to glass, which minimizes light bending and improves the resolution and clarity of the image.

Why other options are wrong

A. To enhance color contrast

Immersion oil does not directly enhance color contrast. Its primary function is to improve resolution by reducing refraction, not altering the color of the image.

C. To increase the magnification

Immersion oil does not increase magnification. The 100X objective lens itself provides the magnification. The oil helps to enhance the image quality by improving resolution, but it does not change the magnification power.

D. To prevent lens fogging

Immersion oil is not used to prevent lens fogging. Fogging is typically caused by condensation or environmental factors, while immersion oil addresses issues related to light refraction to enhance clarity.

Correct Answer A. Fully down

Explanation

When storing a microscope, it is recommended to leave the stage fully down to prevent any damage to the lenses and the stage itself. This ensures that the objective lenses are safely away from any potential contact with the slide or stage, reducing the risk of scratching or damaging the lenses. Additionally, lowering the stage when not in use helps protect the microscope and extends its lifespan.

Why other options are wrong

B. Middle

This is incorrect because leaving the stage in the middle position may still expose the objective lenses to potential damage or misalignment. It is safest to lower the stage fully when storing the microscope.

C. Central

This is incorrect because the "central" position is not a standard term for positioning the stage and does not specifically help in preventing damage to the microscope. The stage should be in the fully down position to ensure safe storage.

D. Fully up

This is incorrect because leaving the stage fully up increases the risk of the objective lenses coming into contact with a slide or the stage, which could lead to scratching or damaging the lenses. The stage should be fully down to avoid these risks.

Correct Answer A. To identify the presence of the enzyme catalase in bacteria

Explanation

The catalase test is primarily used to identify the presence of the enzyme catalase in bacteria. Catalase breaks down hydrogen peroxide into water and oxygen, which results in the production of bubbles. This test is important for distinguishing between different bacterial species, such as differentiating Staphylococci (catalase-positive) from Streptococci (catalase-negative).

Why other options are wrong

B. To determine the antibiotic susceptibility of bacteria

The catalase test is not related to antibiotic susceptibility. Antibiotic susceptibility is typically determined through methods like the disk diffusion test or broth dilution, not catalase testing.

C. To differentiate between Gram-positive and Gram-negative bacteria

The catalase test does not differentiate between Gram-positive and Gram-negative bacteria. It is used to identify whether a bacterium produces catalase, which is more relevant to species identification, not Gram staining.

D. To assess the fermentation capabilities of bacteria

Fermentation capabilities are assessed through different biochemical tests, such as carbohydrate fermentation tests, not through the catalase test. The catalase test focuses solely on the breakdown of hydrogen peroxide.

Correct Answer

B. It isolates a single type of microorganism for further study

Explanation

Subculturing an isolated colony is an effective way to ensure that the culture is pure because it allows the growth of a single type of microorganism. When a colony is isolated on an agar plate, it ideally represents a population of one species. By transferring the colony to a fresh medium, we can determine whether the isolated species grows independently, which confirms that no other species are contaminating the culture. This method is essential for obtaining pure cultures for further study and accurate experimental results.

Why other options are wrong

A. It allows for the growth of multiple species

This is incorrect because the goal of subculturing an isolated colony is to isolate a single species, not to encourage the growth of multiple species. If multiple species are growing, the culture is not pure.

C. It speeds up the growth process

Subculturing does not necessarily speed up growth; it is primarily used to obtain a pure culture. The speed of growth is dependent on the organism and environmental factors, not the subculturing process itself.

D. It reduces the need for staining techniques

Subculturing does not eliminate the need for staining techniques. Staining is often still required to observe the morphology and characteristics of the microorganisms, especially under a microscope. Subculturing helps ensure purity, but it does not replace the need for staining.

Correct Answer B. It is used to initiate microbial growth in a culture

Explanation

An inoculum refers to a small sample of microorganisms, such as bacteria or fungi, that is transferred to a culture medium to initiate microbial growth. The inoculum serves as the starting point for growing cultures and is critical for microbiological experiments. It can be obtained from a variety of sources, including environmental samples, clinical specimens, or laboratory cultures, and is used to establish the conditions under which the microorganisms can grow and be studied.

Why other options are wrong

A. It serves as a control sample

This is incorrect because the inoculum is not a control sample. A control sample is used in experiments to compare results with experimental groups and assess the effect of various variables, whereas the inoculum is used to introduce microorganisms to a culture.

C. It prevents contamination of cultures

This is incorrect because the inoculum does not serve to prevent contamination; it is used to introduce microorganisms into a sterile medium. To prevent contamination, proper aseptic techniques are used when handling the inoculum and culturing microorganisms.

D. It is a method for staining microorganisms

This is incorrect because an inoculum is not a method for staining microorganisms. Staining techniques are separate procedures used to make microorganisms more visible under a microscope, whereas an inoculum is the sample of microorganisms introduced into a culture for growth.

Correct Answer B. Accidental contamination leading to unreliable results

Explanation

If a microbiologist fails to recognize the ubiquity of microorganisms, they might not take adequate precautions to avoid contamination. This could lead to the introduction of unwanted microorganisms into the culture, which would compromise the experiment and lead to unreliable results. Proper aseptic techniques are crucial to maintaining pure cultures and obtaining valid experimental outcomes.

Why other options are wrong

A. Increased growth of desired bacteria

Failing to appreciate the ubiquity of microorganisms typically results in contamination, not in increased growth of the desired bacteria. Contamination could overshadow the growth of the target bacteria.

C. Enhanced immune response in the culture

The immune response would only be relevant if an organism's immune system were involved in the experiment, which is not typically the case in microbiological culture work. The main issue in failing to control microorganism ubiquity is contamination.

D. Improved visualization under the microscope

Improper handling of cultures is unlikely to improve visualization; it may, in fact, hinder clarity by introducing unwanted organisms into the specimen.

Correct Answer

A. An inanimate object upon which pathogens can be conveyed

Explanation

A fomite is any non-living object or surface that can carry and transfer infectious agents. Examples include doorknobs, medical instruments, clothing, and countertops. While fomites do not cause disease directly, they can act as a vehicle for pathogens, contributing to disease transmission in hospitals, labs, and everyday environments.

Why other options are wrong

B. Any microbe that causes disease.

A disease-causing microbe is called a "pathogen," not a fomite. A fomite is the surface or object that carries the pathogen.

C. A substance that kills bacteria.

A substance that kills bacteria is called a "disinfectant" or "antibiotic," not a fomite. Fomites, in contrast, are objects that can harbor bacteria rather than eliminate them.

D. A living carrier that transmits disease.

A living carrier that spreads disease (such as a mosquito or tick) is called a "vector," not a fomite. Fomites are always non-living objects.