Microbiology with Lab: A Fundamental Approach (D311)

Correct Answer B. Stains that are negatively charged and color the background around the cells

Explanation

Anionic stains are negatively charged dyes that are repelled by the negatively charged components of bacterial cells, such as the cell wall. Instead of coloring the cells themselves, these stains color the background surrounding the cells. This is useful in negative staining techniques, where the bacterial cells remain clear, and the background is stained, allowing for better contrast.

Why other options are wrong

A. Stains that are positively charged and color the cells themselves

This describes cationic stains, which are positively charged and bind to the negatively charged components of the cell, coloring the cells themselves. This is the opposite of what anionic stains do.

C. Stains that are neutral and do not affect the color of the cells

Neutral stains do not exist in the context of microbiological staining. Stains either have a positive or negative charge, affecting how they interact with the cells.

D. Stains that are used exclusively for gram staining

Anionic stains are not used exclusively for gram staining. Gram staining uses crystal violet (cationic) and iodine, along with decolorizer and counterstain (safranin), which are not anionic.

Correct Answer B. Wrapped in a paper towel and disposed into the biohazard bin

Explanation

Used slides, especially those that have been in contact with bacterial cultures or staining reagents, must be disposed of properly to prevent contamination or infection. The correct disposal method is to wrap the slide in a paper towel and place it in the biohazard bin, which is designated for items that may be contaminated with microorganisms or harmful substances.

Why other options are wrong

A. Placed in the regular trash

This is incorrect because disposing of contaminated slides in regular trash poses a health risk. They must be handled as bio hazardous materials to prevent potential exposure to harmful microorganisms.

C. Rinsed with water and reused

This is incorrect because reusing slides that have been contaminated with microorganisms or staining reagents can lead to cross-contamination and inaccurate results. Proper disposal is required to maintain safety and cleanliness.

D. Returned to the microscope cabinet

This is incorrect because used slides should not be returned to the microscope cabinet. Storing contaminated slides improperly could lead to contamination of other equipment or surfaces in the laboratory.

Correct Answer A. The capacity of bacteria to withstand the effects of a harmful agent

Explanation

Antibiotic resistance refers to the ability of bacteria to resist the effects of drugs that would normally kill or inhibit their growth. This resistance can occur through genetic mutations or acquiring resistance genes from other bacteria. Resistant bacteria are able to survive and proliferate even in the presence of antibiotics, making infections more difficult to treat.

Why other options are wrong

B. The inability of bacteria to grow in the presence of antibiotics

This is the opposite of resistance. If bacteria are unable to grow in the presence of antibiotics, they are considered susceptible, not resistant. Resistance means the bacteria can still grow despite the presence of the antibiotic.

C. The effectiveness of antibiotics in killing bacteria

This option refers to the activity of antibiotics, not resistance. Resistance means the bacteria can evade the antibiotic's effects, while this option is about how well the antibiotic works, which is unrelated to resistance.

D. The process by which antibiotics are absorbed by bacteria

This is not related to resistance. Antibiotic absorption by bacteria refers to how the drugs enter the bacteria, but resistance is about the bacteria’s ability to survive and grow despite the antibiotic's presence.

Correct Answer

C. To minimize the risk of injury to personnel

Explanation

Disposing of broken glass slides in a designated container helps minimize the risk of injury to personnel. Broken glass can cause cuts or puncture wounds, and when disposed of improperly, it may pose a significant hazard to those handling the trash. A designated broken glass container is typically made of durable material and has a safety mechanism to prevent injuries during handling and disposal.

Why other options are wrong

A. To prevent contamination of other waste

While broken glass could potentially contaminate other waste, the primary concern is preventing injury. Containment in a proper receptacle is crucial to minimize injury, even if it also prevents contamination.

B. To ensure the glass is recycled properly

The primary concern with broken glass is safety, rather than recycling. Though recycling might occur, the main reason for designated disposal is to prevent injury.

D. To comply with laboratory safety regulations

While complying with safety regulations is important, the primary reason for using a designated container is the direct prevention of injury from broken glass. Regulations are in place to support this safety measure.

Correct Answer A. By competing for nutrients and space

Explanation

Microbiota, or the normal flora of microorganisms, play a protective role in preventing pathogenic organisms from colonizing the human body. One of the primary mechanisms they use is competition for resources, such as nutrients and space. By occupying ecological niches in the body, normal microbiota can limit the ability of pathogens to establish themselves, essentially outcompeting harmful microbes for the available resources.

Why other options are wrong

B. By producing harmful toxins

This is incorrect. While some bacteria in the microbiota may produce toxins, this is not typically how microbiota prevent colonization of pathogens. The presence of microbiota mainly prevents pathogen colonization through competition, not by producing harmful substances.

C. By increasing the pH of the skin

This is incorrect. The pH of the skin may be influenced by the microbiota, but it is not the main mechanism by which they prevent pathogen colonization. The primary method of prevention is through competition for space and resources.

D. By directly attacking pathogens

This is incorrect. While some microbiota may produce antimicrobial compounds, their primary defense mechanism is through competition for resources, not direct attack of pathogens. The body’s immune system is more responsible for actively attacking pathogens.

Correct Answer A. Student name, date of inoculation, identity of organism or source, and the name of the nutrient media

Explanation

The minimum requirements for a label in a microbiology laboratory should include the student's name, the date of inoculation, the identity of the organism or its source, and the name of the nutrient media used. These details ensure proper tracking and identification of cultures, preventing contamination or misidentification during incubation or analysis. A thorough label helps maintain clear records and supports the reproducibility of experiments.

Why other options are wrong

B. Name of nutrient media, depth of petri plate, and a prediction of how many colonies will appear after incubation

This is incorrect because predicting the number of colonies and noting the depth of the petri plate are not minimum labeling requirements. While useful for certain experiments, they are not necessary for the basic identification and tracking of cultures.

C. Student name and temperature of incubation

This is incorrect because the temperature of incubation alone is insufficient. The label must also include essential details like the organism's identity and the date of inoculation to track the experiment properly.

D. Student name, date of inoculation, and name of organism or source

This is incomplete. While these elements are necessary, the name of the nutrient media used is also an important labeling detail. It ensures the correct media was used for the growth and analysis of the organism.

Correct Answer

A. Microbes in quadrant 3 have more space and nutrients

Explanation

In streak plate techniques, as the streaking progresses from quadrant 1 to quadrant 3, the bacteria are increasingly diluted, leading to fewer cells in quadrant 3. The cells in quadrant 3 thus have more space and nutrients, allowing them to grow into larger colonies compared to quadrant 1. In quadrant 1, the concentration of bacteria is higher, leading to smaller colonies because the available nutrients are being consumed quickly.

Why other options are wrong

B. Microbes in quadrant 1 are older

This is incorrect because the age of the microbes does not significantly impact the size of the colonies in the context of streaking. The size of the colonies is primarily determined by the available nutrients and space, not by the age of the microorganisms.

C. Quadrant 3 has a different temperature

This is incorrect because, in a typical streaking process, the temperature remains constant throughout the plate. Variations in temperature could affect colony growth, but this is not the primary reason for the size difference between the quadrants.

D. Quadrant 1 has more contaminants

This is not correct because quadrant 1 contains the initial inoculum, which typically has a higher density of bacteria. The colony size difference is due to the dilution of bacteria in subsequent quadrants, not because of contamination.

Correct Answer

B. 4 degrees Celsius

Explanation

The recommended temperature for storing microbial cultures for future observations is 4 degrees Celsius. This temperature slows down the growth of most microorganisms, allowing cultures to be preserved without significant metabolic activity. It helps maintain the viability of the organisms without allowing them to multiply excessively or die from heat exposure. Storing cultures at 4 degrees Celsius is commonly used for preserving bacterial strains and preventing contamination while keeping them stable for long-term observation.

Why other options are wrong

A. Room temperature

Storing microbial cultures at room temperature can lead to uncontrolled growth, which could alter the culture or lead to contamination. Room temperature is not ideal for long-term storage because it encourages microbial activity, leading to changes over time.

C. 20 degrees Celsius

While this temperature is cooler than room temperature, it is still too high for optimal preservation of microbial cultures. Many microorganisms could grow and alter their characteristics at 20 degrees Celsius, making it unsuitable for long-term storage.

D. 37 degrees Celsius

37 degrees Celsius is the optimal growth temperature for many human pathogens, but it is too high for storing microbial cultures. At this temperature, cultures would continue growing, which could lead to overgrowth, contamination, or other changes that make them unsuitable for future study.

Correct Answer B. A negatively charged dye

Explanation

An anionic chromagen is a dye that carries a negative charge. In microbiology, such dyes are used in certain staining techniques, such as negative staining, where the dye repels from the microorganism and stains the background, allowing the cells to stand out. These dyes interact with the positively charged structures on the bacterial cell surface, which helps to create a clear contrast during microscopic examination.

Why other options are wrong

A. A positively charged dye

This is incorrect because positively charged dyes are called cationic chromagens, not anionic. These dyes interact with negatively charged components on the surface of cells, which is the opposite of what is described for anionic chromagens.

C. A neutral dye

This is incorrect because a neutral dye does not carry a charge, whereas an anionic chromagen specifically carries a negative charge. The concept of a neutral dye does not align with the definition of an anionic chromagen.

D. A dye that changes color with pH

This is incorrect because a dye that changes color with pH is referred to as a pH indicator, not an anionic chromagen. Anionic chromogens do not rely on pH for their function but rather on their negative charge to create contrast in staining techniques.