Microbiology Lab Exam #1

The function of the iris diaphragm is to adjust the amount of light coming through the abbe condenser. Ideally, it should be set in the middle so that when looking through the lens, the light is not blinding. It helps control the amount of light that reaches the specimen, allowing for better visibility and clarity during microscopy.

Oil immersion is a technique used in microscopy to increase the resolving power and clarity of the image. It involves placing a drop of oil between the specimen and the objective lens. The oil has a refractive index similar to that of glass, which reduces the loss of light due to refraction. The total magnification for oil immersion is typically higher than other types of microscopy, such as dry lenses, because the oil allows for higher numerical aperture. Therefore, the correct answer of 1000 indicates that the total magnification for oil immersion is 1000x.

Normal flora refers to the microorganisms that naturally reside on various mucosal surfaces of the body, such as the skin, respiratory tract, gastrointestinal tract, and urogenital tract. These microorganisms, including bacteria, fungi, and viruses, coexist with the human body in a symbiotic relationship. They provide benefits such as aiding in digestion, producing vitamins, and preventing the colonization of harmful pathogens. Therefore, the correct answer is that normal flora grows on different mucosal surfaces of the body.

The purpose of oil immersion is to use oil to replace air and prevent refraction at a glass-air interface. When examining specimens under a microscope, using oil immersion helps to increase the resolution and clarity of the image. By replacing the air between the glass slide and the objective lens with oil, the light rays can pass through without any refraction or distortion, resulting in a sharper image. This technique is commonly used in high-power microscopy, especially in fields like microbiology and pathology.

Serratia is a type of bacteria that is commonly red in color at room temperature. This color is due to the production of a red pigment called prodigiosin, which gives the bacteria its distinctive red appearance. Therefore, the correct answer is red.

Inverting plates during incubation helps to prevent the buildup of condensation that could potentially ruin the culture. By placing the agar side on top, any condensation that forms will fall away from the bacterial colonies, reducing the risk of contamination or interference with the growth of the culture. This method also helps to ensure that the agar remains intact and that the bacteria do not dissolve into the agar or clump together unnecessarily.

Parfocal lenses are designed to maintain focus when switching between objectives, meaning that little adjustment of the fine focus knob is necessary. This allows for smooth and efficient transitions between different magnifications without losing focus on the specimen. The iris diaphragm and Abbe condenser are not directly related to the ability to maintain focus when switching objectives.

The red colored objective is called scanning.

The correct answer is oil immersion. Oil immersion is the real name of the white-rimmed objective. This type of objective lens is used in microscopy to achieve higher magnification and resolution by immersing the lens in a special oil with a refractive index similar to that of glass. This allows for better light transmission and minimizes the loss of light due to refraction.

The total magnification of a microscope is calculated by multiplying the magnification of the objective lens with the magnification of the eyepiece. In this case, the question specifically asks for the magnification of the scanning objective. Since the answer provided is 40, it can be inferred that the scanning objective has a magnification of 40.

The total magnification for high-dry is 400. This means that the image seen through the high-dry objective lens appears 400 times larger than the actual size of the specimen.

The correct answer is "high-dry" because it refers to a type of objective lens used in microscopy. High-dry objectives have a blue rim around them, which helps to distinguish them from other types of objectives. They are designed for use with a coverslip and a thin layer of immersion oil, allowing for higher magnification and resolution compared to low-dry objectives. Scanning objectives, on the other hand, are used for low magnification and are not characterized by a blue rim.

Mycobacterium is a group of organisms that are considered acid-fast. Acid-fast organisms have a unique cell wall structure that allows them to retain a stain even when exposed to acid. This property is mainly due to the presence of a waxy substance called mycolic acid in their cell walls. Mycobacterium includes important pathogens such as Mycobacterium tuberculosis, which causes tuberculosis, and Mycobacterium leprae, which causes leprosy. These organisms are difficult to stain and are resistant to many disinfectants, making them challenging to treat and control.

The correct answer is low-dry because it refers to a type of objective lens commonly used in microscopy. Low-dry objectives have a lower magnification power compared to high-dry or oil immersion objectives. They are designed for viewing specimens that do not require high levels of magnification and are often used for initial scanning or locating specific areas of interest on a slide. The term "low-dry" comes from the fact that these objectives are typically used with a lower amount of immersion oil or no oil at all.

If there is no growth observed after 48 hours of incubation, it suggests that the subcultures were not properly inoculated with bacteria. Forgetting to inoculate means that no bacteria were added to the plate, resulting in no growth. Another possible error could be the use of an un-cooled needle to transfer the bacteria, which could have killed the bacteria due to the heat.

First, the ocular lenses should be cleaned with an alcohol swab and then wiped with a lens paper to polish them (step 2). Next, the yellow, blue, and white objectives should be cleaned (step 3). Finally, the stage should be cleaned using a used alcohol swab (step 1). This order ensures that the lenses are properly cleaned and polished before moving on to clean the objectives and stage.

The total magnification for low-dry is 100.

To enhance isolation of bacteria, two important steps should be followed. Firstly, after the primary inoculum, it is necessary to flame and cool the needle. This helps to sterilize the needle and prevent any contamination. Secondly, it is important to have a firm touch while handling the bacteria and avoid scooping. This ensures that the bacteria are properly isolated and prevents cross-contamination.

Lysogeny is a fascinating example of viral reproduction where the bacteriophage, a virus that infects bacteria, doesn't immediately kill its host. Instead, it inserts its DNA into the bacterium's chromosome, becoming a prophage. This prophage replicates along with the bacterial DNA, remaining dormant for generations. Certain environmental triggers can cause the prophage to activate, leading to the production of new phages and the lysis (destruction) of the bacterial cell. This complex relationship between virus and bacteria highlights the intricate interactions in the microbial world.

The five characteristics of bacterial colonial morphologies are differences in size, shape, color or pigment, texture, and density. These characteristics describe the physical appearance of bacterial colonies and can vary greatly depending on the species and conditions in which they grow. Size refers to the overall dimensions of the colony, shape describes the form or outline of the colony, color or pigment refers to the pigmentation or lack thereof in the colony, texture describes the surface or consistency of the colony, and density refers to the compactness or thickness of the colony. These characteristics are important for identifying and classifying different bacterial species.

Leaving a petri dish open for an extended period of time can lead to air contamination. This is because the open dish allows airborne particles, such as dust, bacteria, or fungi, to settle on the agar surface. These contaminants can interfere with the growth of the desired microorganisms and introduce unwanted organisms into the culture. To maintain a controlled environment and prevent contamination, petri dishes should be covered and sealed properly after inoculation.

The correct answer is broth or agar based. Media refers to the substance used to cultivate and grow bacteria in a laboratory setting. It provides the necessary nutrients and environment for bacterial growth. In this case, the "base" refers to the medium on which bacteria are added. It can either be a broth or agar-based medium, both of which are commonly used in microbiology for bacterial culture.

Agar is a substance that is commonly used in laboratories as a solid form of media. It provides a solid surface for the growth of microorganisms. Agar is derived from seaweed, specifically red algae. It is extracted from the cell walls of these algae and then processed into a gel-like substance. Agar is preferred over other types of media because it is inert, meaning it does not react with the microorganisms being cultured. It also has a high melting point, allowing it to remain solid at higher temperatures, making it suitable for a wide range of experiments.

Culture tubes are held at an angle to prevent air contamination because when the tube is tilted, the risk of airborne particles entering the tube is reduced. By keeping the opening of the tube facing downwards, gravity helps to prevent any contaminants from falling into the culture. This is particularly important in microbiology, where maintaining a sterile environment is crucial for the growth and study of microorganisms. Holding the culture tube at an angle is a simple yet effective measure to minimize the risk of air contamination and maintain the integrity of the culture.

Sheep's blood is used as a media for fastidious bacteria because it provides the necessary nutrients that these bacteria require for growth. Fastidious bacteria are unable to synthesize certain essential nutrients on their own and therefore rely on external sources. Sheep's blood contains a variety of nutrients, such as vitamins, minerals, and amino acids, that can support the growth and metabolism of these bacteria. By using sheep's blood as a media, it ensures that the fastidious bacteria have access to the extra nutrients they need to survive and thrive.

The correct answer includes four places where normal flora exists: the GI tract, vagina, throat, mouth, and sinuses. Normal flora refers to the microorganisms that naturally inhabit these areas of the body without causing harm. The GI tract is home to a diverse range of bacteria that aid in digestion. The vagina has a unique microbial community that helps maintain a healthy pH balance. The throat, mouth, and sinuses also have their own populations of bacteria that play a role in oral and respiratory health.

The Abbe condenser is a device used in microscopy to enhance the illumination of the specimen. It collects light from the light source and focuses it onto the specimen, increasing the intensity and uniformity of the light. By condensing the light, it improves the resolution and contrast of the image. Additionally, the Abbe condenser can also serve as an alternate light source when the primary light source is not available or not suitable for the specific observation.

The ways to determine if media is sterile are by running controls, observing no floaters in agar, and observing no growth in broth. Running controls involves using a sample of the media without any bacteria to ensure that the media itself is not contaminated. If there are no floaters in the agar, it indicates that there are no visible contaminants present. Similarly, if there is no growth in the broth, it suggests that there are no viable microorganisms present in the media. These methods help to confirm the sterility of the media.

The total magnification is calculated by multiplying the magnification of the objective lens with the magnification of the ocular lens. This equation is used to determine the overall magnification of a microscope. The objective lens is responsible for magnifying the image of the specimen, while the ocular lens further magnifies the image for the observer. By multiplying these two magnifications together, the total magnification of the microscope can be determined.

The Gram stain is a crucial differential staining technique used in microbiology to classify bacteria into two major groups: Gram-positive and Gram-negative. This classification is based on the differences in cell wall compositions of the bacteria, which affect how they retain the crystal violet dye during the staining process. Gram-positive bacteria retain the dye and appear purple, whereas Gram-negative bacteria do not and appear pink after a counterstain. This technique helps in determining appropriate treatment strategies and understanding bacterial structure.

The question is asking for the four microscopic morphologies of bacteria. The correct answer includes four different shapes: cocci, coccobacilli, bacilli, and spirals. Cocci are spherical-shaped bacteria, coccobacilli are oval-shaped bacteria, bacilli are rod-shaped bacteria, and spirals are spiral-shaped bacteria. These different morphologies are important for classifying and identifying different types of bacteria.

Streaking for isolation refers to a technique used in microbiology to separate and obtain pure colonies of bacteria or other microorganisms. It involves streaking a sample onto a solid growth medium in a pattern that gradually dilutes the cells, leading to the formation of isolated colonies. In the context of the given answer, streaking for isolation is used to break up colonies from two different species, allowing for the separation and identification of individual species present in a mixed sample.

The three optical parts of a microscope are the eyepiece, abbe condenser, and objective lens. The eyepiece is the part that you look through to view the specimen, while the abbe condenser is responsible for focusing and directing light onto the specimen. The objective lens is the part that is closest to the specimen and magnifies the image. Together, these three parts work in conjunction to provide a clear and magnified view of the specimen under the microscope.

A positive acid-fast stain appears as fuscia/pink clusters of rods and blue cocci. This staining technique is used to identify bacteria that have a waxy cell wall, such as Mycobacterium tuberculosis. The waxy cell wall prevents the stain from being washed out, resulting in the bacteria retaining the pink color. The blue cocci mentioned in the answer might be unrelated to the acid-fast stain, as cocci are typically round-shaped bacteria and not commonly stained using this technique.