Microbiology MCQs with Answer and Explnation | Chapter 8

Answer: Drying

Drying, as a method of sterilization, does not effectively eliminate spores. While it can reduce microbial growth by removing moisture, it doesn’t destroy spores entirely. Spores are highly resilient structures and require specific methods like autoclaving or other forms of high heat, pressure, or chemical treatments to ensure their destruction.

Incorrect options:

1. Hot air oven: This method uses high temperatures for sterilization and can effectively eliminate most microbes, including spores, given the right temperature and duration.
2. Autoclave: Autoclaving involves high-pressure steam to sterilize materials and is highly effective against spores. It’s one of the most reliable methods for complete sterilization.

Answer: Chilling

Chilling refers to the process of preserving food materials at a temperature just above freezing. It’s a method used to slow down microbial growth and enzymatic reactions in food by keeping it at a low but not freezing temperature.

Incorrect options:

1. Freezing: Freezing involves lowering the temperature of food below its freezing point, typically to preserve it for longer periods by stopping microbial growth and enzymatic activity completely.
2. Pasteurization: This process involves heating food to a specific temperature to kill pathogens and extend shelf life. It’s not specifically related to preserving food at temperatures just above freezing.
3. Frosting: Frosting refers to the formation of ice crystals on the surface of food due to freezing, but it’s not a preservation method itself; rather, it’s a consequence of freezing.

Answer: U.V. rays

UV rays have the capability to induce dimerization of thymine bases within DNA molecules. Specifically, UV radiation can cause adjacent thymine molecules to form covalent bonds between their bases, resulting in the creation of thymine dimers. These dimers can distort the DNA structure and interfere with normal cellular processes like replication and transcription.

Incorrect options:

1. X-rays: While X-rays can cause damage to DNA, they do not induce dimerization specifically in thymine bases.
2. Gamma (ã)-rays: Gamma rays are high-energy electromagnetic radiation that can cause various types of DNA damage, but they do not induce thymine dimerization as their primary effect.

Answer: γ-rays

Ionizing radiation refers to radiation that carries enough energy to remove tightly bound electrons from atoms, thus ionizing them. Gamma (γ)-rays are a type of electromagnetic radiation that possesses high energy and can ionize atoms, causing damage to biological tissues by breaking chemical bonds and causing cellular damage.

Incorrect options:

1. U.V. rays: Ultraviolet (UV) rays have less energy compared to ionizing radiation and do not have the ability to ionize atoms.
2. IR (Infrared): Infrared radiation also lacks the energy required to ionize atoms and is not considered ionizing radiation. It has lower energy than visible light and is commonly associated with heat rather than ionization.

Answer: Isolation

When a single bacterial colony is separated from a mixed population and grown independently, it’s termed as isolation. This process allows for the cultivation of a pure culture derived from a single organism.

Incorrect options:

1. Separation: While separation is involved in the process of isolating a bacterial colony, the specific term used for this action is “isolation” in microbiology.
2. Pure culturing: Pure culturing involves growing a microorganism in a culture medium, often derived from a single cell or colony, but it doesn’t specifically refer to the initial separation of a single colony.

Answer: Corynebacterium glutamicum

L-Lysine, an essential amino acid, is commonly produced through fermentation processes involving Corynebacterium glutamicum. This bacterium has been extensively used in industry for the large-scale production of amino acids, including L-lysine, due to its ability to efficiently synthesize these compounds.

Incorrect options:

1. Clostridium botulinum: This bacterium is not known for L-lysine production but is associated with producing botulinum toxin, which causes botulism.
2. Mycobacterium sps: Mycobacterium species are not commonly associated with the large-scale industrial production of L-lysine.
3. Pseudomonas: While Pseudomonas species have industrial applications, they are not typically employed in the production of L-lysine.

Answer: All of these

Algae are incredibly diverse organisms and can be rich sources of carbohydrates, proteins, and various vitamins. Different species of algae can contain varying proportions of these nutrients, making them valuable for various purposes, including food, supplements, and biofuel production.

Incorrect options:

1. Carbohydrates: While algae can be rich in carbohydrates, they are not exclusively abundant in this nutrient. They also contain other essential compounds like proteins and vitamins.
2. Proteins: Algae can indeed be rich in proteins, but they are not solely abundant in proteins. They contain a variety of nutrients, including carbohydrates and vitamins.
3. Vitamins: Algae can be a source of various vitamins, but they do not exclusively contain vitamins. They also contain carbohydrates, proteins, and other essential nutrients.

Answer: Inoculum

Inoculum refers to the small amount of microorganisms introduced into a culture medium to initiate growth and establish a bacterial culture. In pure culture methods, a specific, isolated microorganism or a single colony is used as the inoculum to start a culture that contains only that particular microbe.

Incorrect options:

1. Suspension: A suspension refers to a mixture of particles or cells dispersed in a liquid medium. While a bacterial culture could be present in suspension, the term used specifically for the culture prepared by pure culture methods is “inoculum.”
2. Dilution: Dilution involves reducing the concentration of a substance by adding more solvent. It’s a process commonly used in laboratories but is not directly related to the bacterial culture prepared by pure culture methods.

Answer: 62.8°C

Pasteurization involves heating food or beverages to specific temperatures for a set duration to kill pathogens and reduce the microbial load while preserving the product’s quality. The most common method, known as high-temperature short-time (HTST) pasteurization, typically employs a temperature of 62.8°C (145°F) for about 15 seconds.

Incorrect options:

1. 35.7°C: This temperature is much lower than the standard pasteurization temperature and is insufficient for effectively reducing microbial content in food or beverages.
2. 68.2°C: While closer to the pasteurization temperature, this temperature doesn’t align with the standard temperature used in the pasteurization process.
3. 60.8°C: Similar to the previous incorrect options, this temperature is not the standard temperature used for pasteurization and does not effectively achieve the purpose of reducing pathogens while preserving product quality.

Answer: Dark field microscope

Dark field microscopy is specifically well-suited for visualizing Treponema pallidum, the bacterium responsible for syphilis. This technique involves illuminating the specimen with oblique or angled light, causing the organisms to appear bright against a dark background, making them easier to observe and identify.

Incorrect options:

1. Fluorescence microscope: While fluorescence microscopy is a powerful tool for visualizing certain structures or organisms tagged with fluorescent dyes, it’s not the primary method used for identifying Treponema pallidum.
2. Bright field microscope: A bright field microscope is a standard microscope that uses a bright background and requires staining to visualize specimens clearly. It is not the most effective method for visualizing Treponema pallidum due to its thin, spiral shape.
3. Flourescence microscope: This option is a misspelling of “Fluorescence microscope” and is a duplicate of the first incorrect option. Fluorescence microscopy is not the most suitable method for identifying Treponema pallidum.

Answer: Separation of a single colony

Isolation is the process of separating a single bacterial colony from a mixed culture. This can be done using a variety of methods, such as streak plating, micromanipulation, or dilution plating. The purpose of isolation is to obtain a pure culture of a single strain of bacteria.

The other options are not correct answers:

• Purification of culture is the process of removing contaminating organisms from a culture. This is not the same as isolation.
• Introduction of inoculum is the process of adding a sample of microorganisms to a culture medium. This is not the same as isolation.
• Grow microorganisms on surfaces is the process of culturing microorganisms on a solid surface, such as an agar plate. This is not the same as isolation.

Answer: Tindalisation

Tindalisation, also known as fractional sterilization, is a method of sterilization that involves heating a substance to a specific temperature for a short period of time, allowing it to cool down, and then repeating the process several times. This process is typically used to sterilize heat-labile substances, such as milk and food.

The other options are not correct answers:

• Pasteurization is a method of sterilization that involves heating a substance to a specific temperature for a short period of time. However, pasteurization does not involve multiple heating cycles.
• Sterilization is the complete removal of all microorganisms from a substance. There are several methods of sterilization, but none of them involve discontinuous heating.
• Fermentation is a metabolic process that occurs in the absence of oxygen. It is not a method of sterilization.

Answer: -15°C to -3°C for 10 min.

Slow freezing is a method of food preservation that involves reducing the temperature of food gradually. This helps to preserve the quality of food by minimizing damage to cells and tissues.

The other options are not correct answers:

• 0°C to 15°C for 15 minutes: This is too fast of a freezing rate for slow freezing.
• 6°C to -10°C for 10 minutes: This is also too fast of a freezing rate for slow freezing.

Answer: 2.0

Theobacillus thiooxidans is an acidophile, meaning it grows best in acidic conditions. The optimal pH for its growth is between 1.0 and 3.0. It can survive in a pH range of 0.0 to 9.0, but it will not grow at pH values above 5.0.

The other options are not correct answers:

• 7.0: This is a neutral pH, and Theobacillus thiooxidans cannot grow at neutral pH.
• 6.0: This is a slightly acidic pH, but it is still too high for Theobacillus thiooxidans to grow optimally.
• 9.5: This is an alkaline pH, and Theobacillus thiooxidans cannot grow at alkaline pH.

Answer: Growth

Growth is the orderly increase in the quantity of all of the cellular components. It is a fundamental process that is essential for all living organisms. Growth allows organisms to increase in size and complexity, and it is also essential for reproduction.

The other options are not correct answers:

• Reproduction is the process of producing offspring. It is a specific type of growth that involves the creation of new cells.
• Binary fission is a type of asexual reproduction that is commonly used by bacteria. It involves the division of a single cell into two identical cells.

Answer: Gram positive bacteria

Lysozyme, an enzyme found in various bodily secretions like tears, saliva, and mucus, is particularly effective against Gram-positive bacteria. It works by breaking down the peptidoglycan cell wall structure found in Gram-positive bacteria, weakening their integrity and leading to bacterial cell lysis. While it has some effect on Gram-negative bacteria, their outer membrane makes them less susceptible to lysozyme compared to Gram-positive bacteria. Lysozyme’s effectiveness against protozoa or helminths is relatively limited compared to its impact on bacterial cell walls.

Answer: Differential medium

Blood agar contains blood, typically sheep or horse blood, added to a nutrient agar base. It’s used to differentiate bacteria based on their ability to hemolyze red blood cells. The presence or absence of hemolysis around bacterial colonies on blood agar helps distinguish different types of bacteria.

Incorrect options:

1. Enrichment medium: Enrichment media contain specific nutrients to encourage the growth of particular microorganisms while inhibiting others. Blood agar, on the other hand, is not primarily used to enrich specific microorganisms.
2. Enriched medium: Enriched media, like blood agar, contain additional nutrients (in this case, blood) to support the growth of a wide variety of microorganisms, but they are specifically utilized for their differential properties.
3. Selective medium: Selective media favor the growth of certain microorganisms while inhibiting others. Blood agar, while it can distinguish different bacteria based on their hemolytic abilities, is not primarily designed to selectively promote the growth of specific microorganisms.

Answer: Dry heat

Infrared radiation employs dry heat to sterilize objects or surfaces. It generates heat energy in the form of electromagnetic waves, which, when directed at the target, can raise the temperature sufficiently to kill microorganisms and achieve sterilization.

Incorrect options:

1. Moist heat: Infrared radiation does not use moisture; instead, it employs dry heat for sterilization.
2. Chemical method: Infrared radiation is not a chemical method of sterilization. It relies on heat energy rather than chemical agents to achieve sterilization.
3. Mechanical method: Infrared radiation is not a mechanical method of sterilization. It does not involve physical mechanisms or moving parts to achieve the sterilization process.

Answer: Red algae

Agar, a gelatinous substance used as a solidifying agent in culture media for microbiological work, is derived from various species of red algae, specifically from the cell walls of these algae.

Incorrect options:

1. Brown algae: Although brown algae also contain certain polysaccharides and components used in various industries, agar is not obtained from brown algae.
2. Green algae: Green algae, despite being a source of many useful compounds, do not produce agar.
3. Blue-green algae: Blue-green algae, also known as cyanobacteria, are not the source of agar. They are a different group of organisms and do not contain agar in their cell walls.

Answer: Standard Plate Count (SPC)

The Standard Plate Count method, often referred to as the Total Viable Count (TVC), is commonly used to estimate the number of viable bacteria present in a sample, such as milk. In this method, diluted samples are spread onto agar plates and then incubated under specific conditions to allow visible colonies to form, which are then counted to estimate the number of viable bacteria present in the original sample.

Incorrect options:

1. Spread plate: The spread plate method involves spreading a known volume of a diluted sample on the surface of an agar plate. While it’s used in microbiology, it may not be the primary method for estimating bacterial counts in milk.
2. Lawn culture: Lawn culture is a technique used to create a dense, uniform growth of bacteria covering the entire agar surface. It’s not specifically used for estimating bacterial counts in milk.
3. Roll tube method: The roll tube method involves rolling a diluted sample onto the surface of a solidified agar medium within a tube. While it’s a technique used in microbiology, it’s not the commonly used method for estimating bacterial counts in milk compared to the Standard Plate Count method.

Answer: Efficiency of a disinfectant

The phenol coefficient is a measure used to compare the effectiveness of a disinfectant against that of phenol (also known as carbolic acid). It indicates the relative disinfecting power of a disinfectant compared to phenol. A phenol coefficient of 1.0 means the disinfectant is as effective as phenol, while values greater than 1.0 suggest higher effectiveness and values less than 1.0 indicate lower effectiveness compared to phenol.

Incorrect options:

1. Dilution of a disinfectant: The phenol coefficient doesn’t measure the dilution of a disinfectant but rather its comparative effectiveness.
2. Purity of a disinfectant: Phenol coefficient doesn’t directly assess the purity of a disinfectant; it’s about how well the disinfectant performs compared to phenol.
3. Quantity of a disinfectant: This term refers to the amount or volume of a disinfectant used, but the phenol coefficient does not measure the quantity of the disinfectant.

Answer: 160°C for 1 hour

A hot air oven is used for sterilization in laboratories and industries. It operates at a temperature of 160°C for a duration of 1 hour to achieve effective sterilization of equipment and materials by denaturing proteins and destroying microbial life.

Incorrect options:

1. 100°C for 1 hour: While 100°C is the boiling point of water and can effectively kill most vegetative forms of bacteria, it may not be sufficient for complete sterilization.
2. 120°C for 1 hour: This temperature is higher than 100°C but still might not guarantee complete sterilization, especially for some heat-resistant microbes and spores.
3. 60°C for 1 hour: 60°C is generally considered within the range of moderate heat and is insufficient for sterilization. It is more suitable for incubation or warming purposes rather than sterilization.

Answer: Freeze-drying

Lyophilization, commonly known as freeze-drying, is a process used to preserve perishable materials or make them more convenient for transport. It involves freezing the material and then reducing the surrounding pressure, allowing the frozen water (ice) to sublimate directly from solid to gas, leaving behind a dried product with minimal damage to its structure.

Incorrect options:

1. Sterilization: Lyophilization is not primarily a sterilization method; its primary purpose is preservation and moisture removal.
2. Burning to ashes: Lyophilization does not involve burning; it’s a gentle process of freeze-drying to remove moisture from materials while preserving their structure.
3. Exposure to formation: This option doesn’t accurately describe lyophilization. The process involves freezing and drying rather than exposure to formation.

Answer: Autoclaving and Hot air over

• Autoclaving is a process that uses steam to destroy microorganisms. It is the most common method of sterilizing glassware because it is effective and reliable. Glassware is typically autoclaved at 121°C (250°F) for 15-20 minutes.
• Hot air oven is a method of sterilizing glassware using dry heat. It is typically used for glassware that cannot withstand the high temperatures of autoclaving. Glassware is typically sterilized in a hot air oven at 160°C (320°F) for 1-2 hours.
• Incineration is a process of burning a substance to ashes. It is not a method of sterilizing glassware.

Answer: Both Glutaraldehyde and Autoclaving

Spores, which are resilient and heat-resistant structures produced by certain bacteria, can be destroyed by high heat and certain chemical agents. Autoclaving, a method that uses high-pressure steam at elevated temperatures, is highly effective in killing spores by denaturing their proteins and disrupting their structures. Glutaraldehyde, a chemical disinfectant, is also capable of killing spores when used at appropriate concentrations and exposure times.

Incorrect options:

1. 70% alcohol: While alcohol-based solutions are effective against many bacteria and some viruses, they might not effectively kill bacterial spores. Spores are generally resistant to the effects of alcohol.
2. Glutaraldehyde: Glutaraldehyde, in fact, is effective against spores. The statement indicating it’s incorrect was a mistake, as it is indeed capable of spore destruction, as mentioned in the correct option.
3. Autoclaving: Autoclaving is indeed effective against spores. The statement indicating it’s incorrect was a mistake, as autoclaving is one of the most reliable methods for spore destruction.

Answer: 120°C

Autoclaves use high-pressure steam to achieve sterilization. The standard temperature required for effective sterilization in an autoclave is around 120°C (250°F) at high pressure. This combination of high temperature and pressure is crucial for destroying microorganisms, including spores, ensuring thorough sterilization of equipment, and materials.

Incorrect options:

1. 50°C: This temperature is too low for effective sterilization. Autoclaves operate at higher temperatures to ensure the destruction of microbes.
2. 100°C: While 100°C is the boiling point of water, it might not be sufficient for complete sterilization, especially for heat-resistant microbes and spores.
3. 180°C: This temperature is higher than the standard requirement for autoclave sterilization. While higher temperatures might be used in specific instances, the standard effective temperature is around 120°C.

Answer: Exaltation

Exaltation refers to the increase or enhancement of virulence in bacteria. It signifies a rise in the ability of a microorganism to cause disease or harm in a host. This can occur through various mechanisms such as mutations, acquisition of new genetic elements, or changes in the bacterial environment that favor increased pathogenicity.

Incorrect options:

1. Pathogenicity: Pathogenicity refers to the capacity of an organism to cause disease, but it doesn’t specifically indicate an increase in virulence; it’s a general term for an organism’s ability to cause harm.
2. Attenuation: Attenuation is the opposite of exaltation; it refers to the weakening or reduction of virulence in a microorganism. It’s often used in vaccine development where a pathogen is deliberately weakened to induce an immune response without causing disease.
3. Toxigenicity: Toxigenicity refers to the ability of a microorganism to produce toxins. While toxins can contribute to virulence, toxigenicity doesn’t necessarily imply an increase in overall virulence of the organism.

Answer: Proteus

Proteus species, notably Proteus mirabilis, are gram-negative bacteria known for their ability to swarm on culture plates. This swarming behavior involves rapid and collective movement of bacteria across the surface of the agar plate, leading to concentric rings and a characteristic appearance.

Incorrect options:

1. Salmonella: Salmonella species are gram-negative bacteria, and they typically do not exhibit swarming behavior on culture plates.
2. Clostridium: Clostridium species are mostly gram-positive bacteria known for their ability to produce endospores. They do not commonly display swarming behavior on culture plates.
3. Staphylococci: Staphylococci are gram-positive bacteria, and while they might exhibit various growth patterns on culture media, swarming is not a typical characteristic associated with this genus.

Answer: Enrichment medium

An enrichment medium is a type of culture medium designed to favor the growth of certain microorganisms by providing specific nutrients or conditions that encourage their growth. When a medium contains an excess of a particular substance other than nutrients to encourage the growth of specific microorganisms, it’s referred to as an enrichment medium.

Incorrect options:

1. Enriched medium: An enriched medium contains additional nutrients, such as blood or serum, to support the growth of fastidious microorganisms. It doesn’t necessarily mean an excess of a specific substance other than nutrients.
2. Special medium: This term is quite general and doesn’t specifically denote the use of excess substances other than nutrients in a culture medium.

Answer: Below 100°C

Pasteurization involves heating a liquid or food product to a temperature below the boiling point of water (100°C) to kill harmful pathogens while retaining the product’s quality. The exact temperature and duration vary depending on the type of pasteurization used (e.g., high-temperature short-time, low-temperature long-time).

Incorrect options:

1. Above 100°C: Pasteurization involves heating below the boiling point of water to preserve the quality of the product. Heating above 100°C would involve boiling, which is not the process used in pasteurization.
2. 100°C: While 100°C is the boiling point of water, pasteurization involves heating below this temperature to maintain the taste and nutritional value of the product while still eliminating harmful microorganisms.

Answer: Only pathogenic forms can be removed

Pasteurization involves heating a liquid or food product to a specific temperature for a defined period to reduce the number of pathogenic microorganisms present, minimizing the risk of foodborne illnesses. It doesn’t guarantee the removal of all microorganisms but aims to target and eliminate or reduce harmful pathogens while preserving the quality of the product.

Incorrect options:

1. All the microorganisms can be removed: Pasteurization does reduce the microbial load, but it doesn’t eliminate all microorganisms. Some heat-resistant or heat-tolerant microbes might survive the process.
2. Only non-pathogenic forms can be removed: Pasteurization primarily targets pathogenic or disease-causing microorganisms while aiming to retain non-pathogenic forms to maintain the product’s taste and quality.

Answer: Living cells

Viruses require living host cells to replicate and propagate. In laboratory settings, viruses are often cultivated using living cells, such as cell cultures or specific host organisms, where the viruses can infect and replicate within these living cells.

Incorrect options:

1. Lab media: While some laboratory media can support the growth of certain viruses for a limited time, viruses generally require living cells for replication, making lab media insufficient for long-term cultivation.
2. Broth: Broth or liquid culture media may support the growth of bacteria or some eukaryotic cells but are not sufficient for culturing viruses, as viruses rely on host cells for replication.

Answer: Tyndall

John Tyndall, a 19th-century physicist and microbiologist, proposed the method of tyndallisation. It involves intermittent boiling of a substance or medium over several days to destroy vegetative bacteria, followed by incubation periods to allow any surviving spores to germinate into vegetative forms, which are then killed by subsequent boiling.

Incorrect options:

1. Pasteur: Louis Pasteur is renowned for his contributions to microbiology, including pasteurization and advancements in germ theory, but he did not propose tyndallisation.
2. Koch: Robert Koch, another influential figure in microbiology, formulated Koch’s postulates for determining the cause of infectious diseases but was not associated with the development of tyndallisation.
3. Jenner: Edward Jenner is famous for developing the smallpox vaccine, a significant advancement in immunology, but he did not propose the method of tyndallisation.

Answer: Inoculation loop

An inoculation loop, typically made of metal wire, is a tool used in laboratories to transfer and streak cultures onto agar plates or slants. It allows for precise and controlled transfer of microorganisms from one location to another for culturing or experimental purposes.

Incorrect options:

1. Slant: A slant is a type of culture medium typically contained in a test tube that is inclined to provide a larger surface area for cultivating microorganisms. It is not a device used for the physical transfer of cultures.
2. Needle: Needles may be used in microbiology for various purposes, including drawing samples or injecting substances, but they are not primarily used to transfer cultures.
3. Autoclave: An autoclave is a device used for sterilization by applying high-pressure steam at elevated temperatures. It is not used for the physical transfer of cultures but rather for sterilizing equipment.

Answer: Streak-plate

Streak-plating involves spreading a mixed culture in a sequential pattern over the surface of an agar plate. Through subsequent streaking, the microbial cells get progressively diluted, leading to isolated colonies that originate from a single microbial cell. This method allows for the isolation and growth of pure cultures.

Incorrect options:

1. Agar slant: While agar slants are used for culturing and maintaining microbial cultures, they may not yield pure cultures as effectively as streak-plating does. Agar slants provide a larger surface area for culturing, but they do not inherently isolate individual colonies.
2. Both Streak-plate & Agar slant: While both streak-plating and agar slants are used in microbiology, streak-plating is specifically designed to obtain pure cultures by isolating individual colonies. Agar slants are primarily used for maintenance and storage of cultures.

Answer: Mac-Conkey’s Agar

MacConkey’s Agar is a selective and differential culture medium primarily used in microbiology to differentiate between lactose fermenting and non-lactose fermenting gram-negative bacteria. Lactose fermenters produce acid during lactose fermentation, which causes a pH change in the agar, turning it pink or red due to the neutral red pH indicator. Non-lactose fermenters do not produce acid and retain the color of the medium.

Incorrect options:

1. Wilson & Lair: This medium isn’t widely recognized in microbiology for differentiating lactose and non-lactose fermenters.
2. Blood Agar: Blood Agar is used to cultivate fastidious microorganisms and to differentiate bacteria based on hemolytic activity but doesn’t specifically differentiate lactose fermentation.
3. Tetra thionate broth: Tetra thionate broth is used for the enrichment and isolation of Salmonella species from clinical specimens but is not utilized for differentiating lactose fermenters.

Answer: Robertson cooked-meat medium

Robertson cooked-meat medium is a type of culture medium specifically designed for the growth of anaerobic bacteria. It consists of pieces of cooked meat suspended in a semisolid gel, creating an environment suitable for the growth of anaerobic organisms by providing nutrients while minimizing exposure to oxygen.

Incorrect options:

1. Nutrient agar: Nutrient agar is a general-purpose medium used for cultivating a wide range of microorganisms, but it does not specifically support the growth of anaerobic bacteria.
2. Nutrient broth: Similar to nutrient agar, nutrient broth is a general-purpose liquid medium used to cultivate a variety of microorganisms, including both aerobic and anaerobic bacteria.
3. MacConkey’s agar: MacConkey’s agar is a selective and differential medium primarily used to differentiate between lactose fermenters and non-fermenters among Gram-negative bacteria but is not specifically designed for anaerobic growth.

Answer: Wilson and Blair

Indicator media contain substances that reveal particular metabolic activities or characteristics of microorganisms by producing visible changes in the medium. Wilson and Blair medium is used to differentiate between sulfate reducers and non-sulfate reducers in microbiology. It contains ferrous sulfate as an indicator, and the formation of black precipitates indicates the reduction of sulfate.

Incorrect options:

1. Nutrient Agar: Nutrient agar is a general-purpose medium containing nutrients for the growth of various microorganisms but does not contain indicators for specific metabolic activities.
2. Nutrient broth: Similar to nutrient agar, nutrient broth is a liquid medium used for the cultivation of microorganisms but does not contain indicators for specific metabolic activities.
3. Czapeck-dox medium: Czapeck-dox medium is used for the cultivation of fungi and contains specific nutrients suitable for fungal growth but is not an indicator medium.

Answer: Both Moist heat and Steam under pressure

Moist heat is more effective at killing microorganisms than dry heat because it can penetrate cells more easily. The steam also helps to break down the cell walls of microorganisms, making them more susceptible to destruction.

The pressure in an autoclave helps to kill microorganisms by increasing the temperature of the steam. This is because the boiling point of water increases with pressure. At 15 psi, the boiling point of water is 121°C, which is hot enough to kill all microorganisms.

Therefore, the principle involved in an autoclave is both moist heat and steam under pressure.

The other option is incorrect:

• Dry heat is not as effective as moist heat for sterilization, and it cannot reach the same high temperatures.

Answer: Hot air oven

heir spores. Complete sterilization can be achieved using either moist heat or dry heat.

• Moist heat is typically used in autoclaves, which use steam under pressure to kill microorganisms. Autoclaves are typically used to sterilize liquids and heat-sensitive materials.
• Dry heat is typically used in hot air ovens, which use high temperatures to kill microorganisms. Hot air ovens are typically used to sterilize dry materials, such as glassware and instruments.

At the temperature of 160°C (320°F) for one hour, complete sterilization can be achieved in a hot air oven. This is because the high temperature will kill all microorganisms, including spores.

List of incorrect options with heading and short brief explanations:

Answer: Incubation

Incubation is the phase in microbiology where cultures are placed in a controlled environment, often at a specific temperature, to allow microorganisms to grow and multiply. During this period, favorable conditions such as temperature, humidity, and nutrients are provided to support the growth of the cultured microorganisms.

Incorrect options:

1. Inoculation: Inoculation refers to introducing a sample into a culture medium or host to initiate growth. It’s the initial step where the sample is introduced into the culture medium for growth.
2. Incineration: Incineration involves burning materials at extremely high temperatures until reduced to ashes. It’s a method used for sterilization or disposal of laboratory waste, not for the growth period of cultures.
3. Isolation: Isolation is the process of obtaining a pure culture by separating individual microbial cells or colonies from a mixed population. It’s not specifically the growth period but rather a step in obtaining a pure culture.

Answer: Both Pure-culturing and Isolation

Pure-culturing is the process of isolating a single type of bacteria from a mixed culture. This is done by transferring a small amount of the culture to a new sterile medium and then incubating it under the appropriate conditions. If the bacteria are able to grow on the new medium, then they are considered to be pure.

Isolation is the process of separating a single colony of bacteria from a mixed culture. This is typically done by using a sterile loop to transfer a small amount of the culture to a new sterile plate. The plate is then incubated under the appropriate conditions and the colonies are allowed to grow. Once the colonies have grown, they can be identified and isolated for further study.

The other option is incorrect:

• Separation is not a specific term in microbiology.

Answer: Inoculum

An inoculum is a suspension of microorganisms that is used to start a new culture. Pure culture inoculum is prepared by isolating a single colony of bacteria and growing it in a culture medium. This ensures that the resulting culture is composed of only one type of bacteria.

Incorrect options:

• Suspension: A suspension is a general term that refers to a mixture of solid particles in a liquid. It is not specific to microorganisms.
• Dilution: Dilution is a process of reducing the concentration of a solution. It is not specific to microorganisms.

Answer: Ethelene oxide

Ethylene oxide is a highly effective sterilizing agent commonly used in healthcare settings and industries for sterilizing heat-sensitive equipment and materials. It works by damaging the DNA and proteins of microorganisms, thereby rendering them unable to multiply or survive.

Incorrect options:

1. Oxygen: Oxygen is not a sterilizing agent. While oxygen is vital for life, it does not possess sterilizing properties.
2. Nitrogen: Nitrogen, like oxygen, is not a sterilizing agent. It is an inert gas and does not have the capability to kill microorganisms.
3. Carbon tetrachloride: Carbon tetrachloride is not used as a sterilizing agent. It’s a chemical compound that was once used in various applications but has been largely phased out due to its toxic and harmful effects on health and the environment.

Answer: Gram positive

Acridine dyes, such as acriflavine and acridine orange, are chemicals used as antimicrobial agents. They are particularly effective against Gram-positive bacteria due to their mode of action, which involves binding to DNA and interfering with its replication and function. Gram-positive bacteria, with their thicker peptidoglycan layer in the cell wall, are more susceptible to these dyes compared to Gram-negative bacteria.

Incorrect options:

1. Gram-negative: Acridine dyes are generally less effective against Gram-negative bacteria due to their outer membrane structure, which acts as a barrier, making it harder for these dyes to penetrate and target the bacterial DNA.
2. Mycoplasmas: Mycoplasmas are bacteria that lack a cell wall. Acridine dyes might have variable effectiveness against Mycoplasmas due to their unique cell structure, but they are generally more effective against bacteria with cell walls like Gram-positives.
3. Rickettsiae: Rickettsiae are intracellular bacteria that cause diseases like typhus and spotted fever. Acridine dyes are not commonly used as treatments for rickettsial infections.

Answer: Both Formaldehyde and Glutamal aldehyde

Both formaldehyde and glutaraldehyde are aldehydes commonly used as powerful disinfectants and sterilizing agents in healthcare settings. They are highly effective against a wide range of microorganisms, including bacteria, viruses, fungi, and spores.

Incorrect options:

1. Formaldehyde: Formaldehyde is indeed a powerful disinfectant, especially in gaseous or liquid form. However, while it’s potent, glutaraldehyde is often considered even more effective against certain microorganisms.
2. Acetaldehyde: Acetaldehyde, while an aldehyde compound, is not typically used as a disinfectant or sterilizing agent to the extent of formaldehyde or glutaraldehyde. It’s more commonly used in chemical processes and as a raw material in certain industries.

Answer: All of the above

The effectiveness or disinfectivity of a disinfectant is influenced by multiple factors, including the concentration of the disinfectant used, the duration or time of action, and the environmental conditions such as the pH of the medium and the temperature at which the disinfectant is applied. Each of these factors can significantly impact the ability of the disinfectant to kill or inhibit the growth of microorganisms.

1. Concentration of the substance: This factor is indeed critical in determining the disinfectant’s effectiveness. However, the disinfectivity also relies on other factors in addition to concentration.
2. Time of action: The duration for which the disinfectant is in contact with the microorganisms is crucial. However, disinfectivity also depends on other aspects beyond just the duration of exposure.
3. pH of the medium and temperature suitable for the chemical: While pH and temperature are vital environmental factors influencing disinfectivity, there are other critical factors that contribute to the effectiveness of a disinfectant as well.

Answer: Bacillus stearothermophilus

Bacillus stearothermophilus is a spore-forming bacterium known for its ability to resist the effects of moist heat. It’s commonly used in sterilization validation processes, especially for evaluating the effectiveness of autoclaves and other equipment that use moist heat for sterilization.

Incorrect options:

1. Bacillus subtilis: While Bacillus subtilis can form spores, it is generally more susceptible to the effects of moist heat compared to Bacillus stearothermophilus.
2. Coxiella burnetii: Coxiella burnetii is the bacterium responsible for Q fever. While it has some resistance to heat, it is not primarily recognized for its resistance to moist heat compared to Bacillus stearothermophilus.
3. Pseudomonas: Pseudomonas is a genus of bacteria known for its diverse characteristics, but it is not particularly known for its resistance to the effects of moist heat like Bacillus stearothermophilus.

Answer: All of these

Thiomersal, Phenyl mercury nitrate, and Mercurochrome are all examples of disinfectants that contain salts of heavy metals. These compounds, containing mercury, are known for their antimicrobial properties and have been used historically as disinfectants or antiseptics. However, their use has been limited or discontinued due to concerns about their potential toxicity.

1. Thiomersal: Thiomersal contains organic mercury and has been used as a preservative in some vaccines and other medical products. Its use has been reduced due to concerns about mercury exposure.
2. Phenyl mercury nitrate: This compound is another example of a disinfectant containing mercury. Its use has also been limited due to concerns about mercury toxicity.
3. Mercurochrome: Mercurochrome is an antiseptic compound containing mercury that was used topically on minor cuts and scrapes. However, its use has been discontinued or restricted due to health concerns associated with mercury exposure.

Answer: Stabcultures

Stab cultures involve inoculating a solid medium by inserting an inoculation loop containing the microbial suspension into the medium, allowing for deep penetration. This method is commonly used for cultivating anaerobic bacteria or for observing motility and growth patterns within the medium.

Incorrect options:

1. Stock cultures: Stock cultures typically refer to a collection of microorganisms maintained for long-term storage and future use, often stored in a preserved or frozen state. Stab cultures are a specific technique for inoculating solid media, not synonymous with stock cultures.
2. Sub-cultures: Sub-cultures refer to the transfer of microorganisms from one medium or culture to another to propagate or maintain the culture. Stab cultures involve a specific method of inoculation rather than being synonymous with sub-cultures.