Test Your Microbiology Skills - Quiz

An organism that is completely dependent on atmospheric O2 for growth is classified as an obligate aerobe. This means that it requires oxygen to carry out its metabolic processes and cannot survive in the absence of oxygen. Obligate aerobes have adapted to utilize oxygen as their terminal electron acceptor in respiration, which is essential for generating energy. Without oxygen, these organisms are unable to produce enough energy to sustain their growth and survival.

A facultative anaerobe is an organism that has the ability to survive and grow in both the presence and absence of oxygen. This means that when oxygen is available, it can use it for its metabolic processes, but it can also switch to alternative pathways to generate energy in the absence of oxygen. Therefore, a facultative anaerobe can adapt its metabolism based on the oxygen availability in its environment.

Psychrophiles are organisms that thrive in cold temperatures. They have adapted to survive and reproduce in environments with low temperatures, such as polar regions or deep ocean waters. These organisms have specific physiological and biochemical adaptations that allow them to function in cold conditions, such as producing antifreeze proteins to prevent ice formation in their cells. Psychrophiles are able to carry out essential biological processes and maintain their metabolism at low temperatures, making them well-suited for cold environments.

Based on the information provided, the student observed that the culture broth tube was turbid at the surface but clear throughout the rest of the tube. This suggests that the organism requires oxygen to grow, as it is concentrated at the surface where oxygen is available. Therefore, the correct conclusion is that the organism is an aerobe, which means it can only grow in the presence of oxygen.

The addition of salt to a culture medium creates a selective environment where only salt-tolerant bacteria can thrive and grow. This is because the high salt concentration inhibits the growth of salt-sensitive bacteria, allowing only the salt-tolerant ones to survive. Selective media is used to selectively promote the growth of specific types of microorganisms while inhibiting the growth of others, making it the correct answer in this case.

Koch is the correct answer because he played a significant role in proving that microorganisms cause disease. He developed several techniques and principles, known as Koch's postulates, which are still used today to identify the causative agents of infectious diseases. Koch's work on tuberculosis and cholera specifically demonstrated the link between specific microorganisms and the diseases they cause. His contributions to the field of microbiology greatly advanced our understanding of infectious diseases and paved the way for the development of effective treatments and preventive measures.

The plate in the figure would be a differential media because it allows most bacteria to grow, but it also distinguishes between colonies of one organism from another. Differential media contains specific ingredients that cause different bacteria to exhibit different visible characteristics, such as color changes or formation of specific patterns, allowing for differentiation between different types of bacteria.

Plates should be incubated agar side up because this allows for proper air circulation and prevents condensation from accumulating on the agar surface. Incubating the plates agar side down could result in the growth of microorganisms on the lid, which can contaminate the agar surface and affect the results of the experiment. Therefore, incubating the plates agar side up is the correct and recommended method.

When streaking a plate, the loop should be flamed at the beginning and end and between each zone. Flaming the loop ensures that any microorganisms present on the loop are killed, preventing contamination of the next zone or the original culture. Flaming also helps to sterilize the loop before and after use, reducing the risk of cross-contamination between different samples. By flaming at the beginning and end and between each zone, the loop is effectively sterilized throughout the streaking process, maintaining the integrity of the culture and preventing unwanted contamination.

Streak plating is a procedure commonly used to isolate a pure culture of a bacterium from a mixture. In this method, a small amount of the bacterial mixture is streaked onto a solid agar plate using an inoculating loop. As the loop is dragged across the surface of the agar, the bacteria are spread out and diluted. This allows for individual bacterial cells to grow into separate colonies. By picking a single colony and transferring it to a new plate, a pure culture of the bacterium can be obtained. Dilution plating and enrichment culture are also valid methods for isolating pure cultures, but the question specifically asks for procedures that can be used, so the correct answer is that all of the above methods can be used.

During the log phase, bacteria are dividing at the fastest possible rate. This phase is characterized by a rapid increase in the number of bacterial cells as they undergo binary fission, where one cell divides into two identical daughter cells. The conditions during this phase are optimal for growth, with abundant nutrients and favorable environmental factors. As a result, the bacteria are able to divide quickly and efficiently, leading to exponential growth and an increase in population size.

Fusobacterium and Clostridium are considered strict anaerobic anaerobes because they cannot survive in the presence of oxygen. They are adapted to environments with low or no oxygen levels and have specific metabolic pathways that allow them to generate energy without the need for oxygen. These organisms are commonly found in the gastrointestinal tract and can cause various infections in humans.

The addition of blood to a culture medium allows for the differentiation of bacteria based on their ability to cause hemolysis, or the breakdown of red blood cells. This is because certain bacteria have the ability to produce enzymes that can lyse red blood cells, resulting in a clear zone around the bacterial colony on the plate. By using blood as a component of the culture medium, only the hemolytic bacteria can be distinguished and picked out, making it an example of differential media.

Endospore staining is the correct answer because it is a specific staining technique used to visualize endospores, which are dormant forms of bacteria. This technique involves the use of heat and specific dyes to differentiate between endospores and other cellular structures. Gram staining is used to classify bacteria into Gram-positive and Gram-negative based on cell wall characteristics. Acid-fast staining is used to identify acid-fast bacteria, such as Mycobacterium tuberculosis. Simple staining is a basic staining technique used to visualize overall cell morphology and size.

When streaking a plate, it is important to place the lid on the bench top with the inside surface facing up. This is because the inside surface of the lid is sterile, while the outside surface may come into contact with potential contaminants on the bench top. Placing the lid with the inside surface up helps to maintain the sterility of the lid and minimize the risk of introducing contaminants to the plate.

Excessive washing should only be a problem if you had not heat fixed your slide; in which case you would have problems anyway.

Besides the three options listed earlier (Sample thickness, bacterial age and reagent quality), excessive rinsing with alcohol and overheating the bacteria will also affect your Gram result.