MicroBiology MCQs with Answer and Explanations | Chapter 68

Answer: Mycobacterium bacilli

Mycobacterium bacilli are acid-fast bacilli, characterized by their ability to retain the stain even when treated with acid alcohol during staining procedures, such as the Ziehl-Neelsen stain. These bacteria include species like Mycobacterium tuberculosis and Mycobacterium leprae, which cause tuberculosis and leprosy, respectively.

The other options are incorrect:

• Treponema pallidum: This bacterium causes syphilis but is not acid-fast. It can be identified through different staining techniques.
• Neisseria gonorrhoeae: This bacterium causes gonorrhea, a sexually transmitted infection. It’s also not acid-fast and requires specific staining methods for detection.
• All of the above: Not all the listed bacteria are acid-fast. Only Mycobacterium tuberculosis exhibits this characteristic.

Answer: Rheumatic fever

Rheumatic fever is a potential complication following a group A beta-hemolytic streptococcal infection, particularly in the pharynx (strep throat). This autoimmune condition affects the heart, joints, skin, and nervous system. Early diagnosis and treatment of the streptococcal infection can help prevent rheumatic fever.

The other options are incorrect:

• Diphtheria: This is a respiratory illness caused by the bacterium Corynebacterium diphtheriae. While it can cause sore throat, it’s not a complication of streptococcal infection.
• Typhoid fever: This bacterial infection caused by Salmonella typhi primarily affects the intestines and doesn’t have a link to streptococcal pharyngitis.
• Syphilis: This sexually transmitted disease is caused by Treponema pallidum and doesn’t have any association with group A streptococcal infections.

Answer: Borrelia vincenti and fusobacterium fusiformis

Vincent’s angina, also known as acute necrotizing ulcerative gingivitis (ANUG), is primarily caused by a polymicrobial infection involving Borrelia vincenti (formerly known as Borrelia fusiformis) and Fusobacterium fusiformis. These bacteria contribute to the characteristic ulcerative lesions and inflammation seen in Vincent’s angina.

The other options are incorrect:

• Borrelia recurrentis and Bacteroides: Borrelia recurrentis is the causative agent of relapsing fever transmitted by lice and ticks. Bacteroides species are anaerobic bacteria commonly found in the human gastrointestinal tract. Neither of these is associated with Vincent’s angina.
• Borrelia burgdorferi and Lactobacillus: Borrelia burgdorferi is the causative agent of Lyme disease, transmitted by ticks. Lactobacillus species are typically found in the human digestive and genital tracts. Neither of these is implicated in Vincent’s angina.
• Leptospira and Treponema pallidum: Leptospira species cause leptospirosis, a zoonotic disease transmitted through water contaminated with animal urine.

Answer: Free of a cell wall and a capsule

A protoplast is a bacterial cell that has lost its cell wall. The cell wall provides rigidity and shape to the bacteria but is absent in a protoplast. Capsules, on the other hand, can still be present in some protoplasts depending on the creation process.

The other options are incorrect:

• With a cell wall but free of a capsule: This describes a typical bacterial cell. Protoplasts lack the defining characteristic – the cell wall.
• Containing a cell wall and a capsule: This is not possible for a true protoplast. The removal of the cell wall is its defining feature.
• Uniquely sensitive to penicillin: While some protoplasts might be more susceptible to antibiotics due to the weakened cell membrane, this isn’t the sole defining characteristic.

Answer: Mesophiles

Most pathogenic bacteria that cause human diseases are mesophiles. This means they thrive at moderate temperatures, typically around human body temperature (around 37°C or 98.6°F). This allows them to efficiently grow and replicate within the human host.

The other options are incorrect:

• Psychrophiles: These bacteria prefer cold environments and wouldn’t be well-suited for infecting humans.
• Cryophiles: Similar to psychrophiles, cryophiles thrive in extremely cold environments and are not suited for human pathogenesis.
• Thermophiles: These bacteria prefer high temperatures and wouldn’t be able to survive and multiply effectively in the human body.

Answer: Irregular clusters

Staphylococci are named for their grape-like clusters (coccus means “berry” and staphyle means “bunch of grapes”). These clusters are irregular in shape and size, unlike some other bacteria that form specific arrangements.

The other options are incorrect:

• Pairs: While some staphylococci might divide and appear in pairs temporarily, irregular clusters are their hallmark.
• Chains: Streptococci, another type of bacteria, typically form chains. Staphylococci do not.
• Tetrads: Tetrads are cube-shaped arrangements of four cells, more commonly seen with bacteria like Neisseria.

Answer: Blood culture

In a patient with typhoid fever, diagnosis after 15 days of onset of fever is best done by blood culture. Blood cultures can detect the presence of Salmonella typhi, the bacterium responsible for causing typhoid fever, in the bloodstream. Culturing blood samples allows for the identification and confirmation of the infection.

The other options are incorrect:

• Widal test: Though used sometimes, it’s less reliable than blood culture after 15 days of fever.
• Stool culture: While positive early on, its effectiveness decreases as the disease progresses.
• Urine culture: Salmonella Typhi is not typically found in urine.

Answer: M-Proteins

Neisseria gonorrhoeae, the bacterium causing gonorrhea, lacks M-proteins. M-proteins are virulence factors commonly found in some gram-positive bacteria like Streptococcus pyogenes (group A strep) and Group B Streptococcus.pen_spark

The other options are incorrect:

• Outer membrane proteins: These proteins play a crucial role in Neisseria gonorrhoeae’s virulence. Some outer membrane proteins help the bacteria adhere to host cells and evade the immune system.
• IgA Protease: This enzyme helps Neisseria gonorrhoeae cleave immunoglobulin A (IgA), an antibody in mucous membranes, which can hinder the bacteria’s ability to infect.
• Pili: These hair-like structures are essential virulence factors for Neisseria gonorrhoeae. They allow the bacteria to attach to and invade host cells.

Answer: Conjugation

Conjugation is a process of horizontal gene transfer in bacteria where genetic material is directly passed from a donor bacterium to a recipient bacterium through a physical connection. This allows the transfer of plasmids, which can carry genes for antibiotic resistance. In vivo refers to within a living organism, highlighting that this exchange happens inside a host (human, animal, etc.).

The other options are incorrect:

• Rarefaction: This term refers to a decrease in the number of species or populations within an environment. It’s not a mechanism for gene transfer.
• Transduction: In transduction, a virus carries bacterial DNA from one bacterium to another. While it can transfer antibiotic resistance genes, it doesn’t involve direct cell-to-cell contact like conjugation.
• Transformation: Transformation involves a bacterium taking up free-floating DNA fragments from the surrounding environment. While it can acquire antibiotic resistance genes, it doesn’t require another living bacterium as in conjugation.

Answer: Logarithmic phase

The logarithmic phase, also known as the exponential phase, is the phase of bacterial growth where cells are actively dividing and increasing in number at a constant rate. It is during this phase that bacterial cultures exhibit uniform staining reaction, consistent morphology, and optimal biochemical activity, making it advisable to study them at this stage.

The other options are incorrect:

• Lag phase: During the lag phase, bacteria are adapting to the new environment and not actively growing. This can lead to uneven staining and difficulty in studying their morphology and biochemical activity.
• Death phase: In the death phase, bacteria are dying or dead. This makes them unsuitable for any meaningful analysis.
• Stationary phase: In the stationary phase, bacterial growth has plateaued due to limitations in resources. Cells might be in various states, affecting staining and analysis.

Answer: Flagella

Flagella are hair-like appendages found in some bacteria that allow them to move. They rotate like a propeller, propelling the bacteria through liquid environments.

The other options are incorrect:

• Fimbriae: Fimbriae are short, hair-like structures on the surface of bacteria. Unlike flagella, they are not used for locomotion. Instead, they help bacteria adhere to surfaces and other cells.
• Capsule: A capsule is a gelatinous layer surrounding some bacteria. It provides protection but doesn’t contribute to movement.
• Cell wall: The cell wall is a rigid structure that gives bacteria their shape and protects them from the environment. It has no role in locomotion.

Answer: Produced by gram positive bacteria

Endotoxins are a specific type of toxin produced by gram-negative bacteria. They are part of the outer membrane of these bacteria and are released when the bacteria die or lyse (break open).

The other options are incorrect:

• Produced by gram negative bacteria: This is the defining characteristic of endotoxins. They are lipopolysaccharides (LPS) found in the outer membrane of gram-negative bacteria.
• Not secreted outside the cell: While endotoxins are not actively secreted by live gram-negative bacteria, they are released into the environment upon cell death or lysis.
• Cannot be toxoided: Toxoids are inactivated toxins that can still trigger an immune response but are not harmful. Endotoxins can be detoxified to varying degrees, depending on the method used.

Answer: Pyrogenic exotoxin

Toxic shock syndrome (TSS) is primarily caused by pyrogenic exotoxins, particularly staphylococcal enterotoxins and toxic shock syndrome toxin 1 (TSST-1) produced by Staphylococcus aureus bacteria. These exotoxins are potent toxins that trigger a massive inflammatory response in the body, leading to the characteristic symptoms of TSS.

The other options are incorrect:

• M protein: M protein is a virulence factor of Streptococcus pyogenes, a different bacterium associated with conditions like strep throat and rheumatic fever. It does not play a role in TSS caused by Staphylococcus aureus.
• Streptolysin O: Similar to M protein, Streptolysin O is another virulence factor of Streptococcus pyogenes and contributes to tissue damage in those infections. It’s not relevant to Staphylococcus aureus-induced TSS.
• Carbohydrate cell wall: While the cell wall of Staphylococcus aureus can interact with the immune system, it’s not the primary factor causing the severe immune response in TSS. Pyrogenic exotoxins are the specific virulence factors responsible for triggering the intense inflammatory cascade.

Answer: Schick test

The Schick test is the most common method used to detect carriers of diphtheria. It involves intradermal injection of diphtheria toxoid. If the individual is susceptible (not immune), they will develop a local reaction at the injection site. Lack of reaction indicates immunity, while a reaction suggests carrier status.

The other options are incorrect:

• Dick test: The Dick test is used to assess immunity to diphtheria and scarlet fever. It involves intradermal injection of small amounts of diphtheria toxin. However, it is not used for detecting carriers of diphtheria.
• Casoni’s test: Casoni’s test is used for the diagnosis of hydatid disease, caused by the tapeworm Echinococcus granulosus. It involves intradermal injection of a purified hydatid cyst fluid extract. It is not related to the detection of diphtheria carriers.
• Charles’ test: There is no commonly known medical test named Charles’ test in the context of diagnosing diphtheria carriers.

Answer: cell wall

The primary difference between gram-positive and gram-negative bacteria lies in the structure of their cell walls. Gram-positive bacteria have a thick layer of peptidoglycan in their cell wall, which retains the crystal violet stain during the Gram staining process, giving them a purple color.

The other options are incorrect:

• Cell membrane: Both gram-positive and gram-negative bacteria have cell membranes, which are essential for basic cellular functions. The cell wall lies outside the cell membrane and provides additional support and protection.
• Nuclear material: Neither gram-positive nor gram-negative bacteria have a true nucleus. They are prokaryotic organisms with their genetic material located in a single, circular chromosome within the cytoplasm.
• Mesosomes: Mesosomes are infoldings of the cell membrane found in some bacteria. While they play a role in some cellular processes, they are not the primary differentiating factor between gram-positive and gram-negative bacteria.

Answer: Most common is animals

Streptococcus is a very common genus of bacteria found widely in nature. While it can be present in animals, Streptococcus species are actually more prevalent in humans. They are part of the normal microbiota (flora) inhabiting various body surfaces like the skin, mouth, throat, and gut.

The other options are incorrect:

• It’s a group of lactic acid production bacteria: Many Streptococcus species are indeed lactic acid bacteria. They ferment sugars to produce lactic acid, contributing to processes like yogurt production and the natural microflora balance in the human body.
• Shows adherence to dental enamel: Streptococcus mutans, a specific species of Streptococcus, is known to adhere to tooth enamel and is a major culprit in dental caries (cavities).
• Most common in humans: This statement best reflects the current understanding of Streptococcus distribution. Streptococcus species are abundant colonizers of humans, playing various roles in health and disease.

Answer: Binary fission

Binary fission is the primary method of reproduction in bacteria. It is a process in which a single bacterial cell divides into two identical daughter cells, each inheriting a copy of the parent cell’s genetic material. This is the most common and efficient way bacteria proliferate.

The other options are incorrect:

• Budding: Budding is a reproduction method used by some yeasts (fungus) where a new organism grows as an outgrowth from the parent cell. It’s not a common mode of reproduction for bacteria.
• Sporing: While some bacteria can form spores for survival under harsh conditions, spore formation is not the primary mode of reproduction. Spores themselves don’t reproduce and germinate back into vegetative cells when conditions improve.
• Bacterial components produced by host cells: Bacteria are self-replicating organisms. They don’t rely on host cells to produce their components for reproduction.

Answer: Pseudomonas aeruginosa

Pseudomonas aeruginosa is an oxidase-positive, gram-negative rod-shaped bacterium known for producing a bluish-green pigment called pyocyanin. It is commonly associated with infections, particularly in burn wounds. In the scenario described, the organism is susceptible to gentamicin, ticarcillin, and tobramycin, but resistant to other antibiotics, which is characteristic of Pseudomonas aeruginosa.

The other options are incorrect:

• Escherichia coli: E. coli is typically oxidase-negative, gram-negative, and doesn’t produce a blue-green pigment.Klebsiella pneumoniae: Similar to E. coli, Klebsiella is usually oxidase-negative and doesn’t produce the characteristic pigment.Proteus mirabilis: Proteus is oxidase-negative, gram-negative, and doesn’t exhibit the blue-green coloration.

Answer: Treponema pallidum

Treponema pallidum is the bacterium responsible for causing syphilis, a sexually transmitted infection. It is a spirochete bacterium that can infect various tissues in the body and cause a wide range of symptoms if left untreated.

The other options are incorrect:

• Borrelia burgdorferi: This bacterium causes Lyme disease, which is transmitted through tick bites and has different symptoms and transmission routes compared to syphilis.
• Chlamydia trachomatis: This bacterium is the most common cause of bacterial sexually transmitted infections (STIs) and manifests differently than syphilis.
• Leptospira interrogans: This bacterium causes leptospirosis, a zoonotic disease spread through contact with infected animal urine. It doesn’t cause syphilis.

Answer: Endo agar

The membrane filter technique is a method used for enumerating and isolating bacteria from liquid samples. In this technique, a membrane filter with specific pore size is placed on a solid medium, usually Endo agar, which is selective for gram-negative bacteria. The bacteria in the liquid sample are filtered through the membrane and then incubated on the selective medium.

The other options are incorrect:

• EMB agar (Eosin Methylene Blue agar): EMB agar is a selective and differential medium commonly used for the isolation and differentiation of gram-negative bacteria, particularly members of the family Enterobacteriaceae. However, it is not typically used in the membrane filter technique.
• EMR-Vp medium: EMR-Vp medium is a differential medium used for the detection of indole production and Voges-Proskauer (VP) reaction in bacteria, particularly coliforms. It is not typically used in the membrane filter technique.
• Lactose broth: Lactose broth is a liquid medium used for the enrichment of lactose-fermenting bacteria. It is not used in the membrane filter technique, which requires a solid medium for bacterial growth and isolation.

Answer: Disinfectant

Disinfectants kill or inactivate a wide range of microorganisms (bacteria, viruses, fungi) on surfaces. Lysol products are designed to be used on surfaces to reduce the risk of infection.

The other options are incorrect:

• Sterilent: Sterilants are even more potent than disinfectants and aim to eliminate all microbial life, including spores. While some Lysol products may have some sporicidal activity, they are not generally classified as sterilants.
• Antiseptic: Antiseptics are typically used on living tissues (skin, wounds) to reduce the risk of infection. While some Lysol products might be suitable for limited topical use (e.g., on minor cuts), they are primarily intended for surface disinfection.
• Antifungal agent: Antifungal agents specifically target and kill fungi. While some Lysol products may have some antifungal activity, they are not primarily designed for this purpose.

Answer: Neutral red

A neutral stain has a minimal electrical charge, meaning it doesn’t readily bind with positively or negatively charged cellular components. This allows it to stain a wider variety of cellular structures without significant bias towards acidic or basic components.

The other options are incorrect:

• Picric acid: Picric acid is an acidic stain with a positive charge. It has an affinity for negatively charged structures like cytoplasm and certain proteins.
• Giemsa stain: Giemsa stain is a complex mixture of several dyes, including both acidic and basic components. It provides detailed staining of various cellular structures based on their charge.
• Malachite green: Malachite green is a cationic stain, meaning it has a positive charge. It primarily stains acidic components like nucleic acids (DNA and RNA) within the cell.

Answer: Semisynthetic medium

Peptone water medium is a type of semisynthetic medium. Semisynthetic media are prepared by mixing natural ingredients (such as peptone, beef extract, yeast extract) with defined chemical components (such as salts and carbohydrates). Peptone water medium contains peptone (partially digested protein), which provides a nitrogen source for bacterial growth, and water.

The other options are incorrect:

• Synthetic medium: As explained above, peptone water contains undefined components from the peptic digest.
• Differential medium: Peptone water doesn’t typically contain ingredients that differentiate bacterial growth. While it can be used as a base for some differential media with additional components, it’s not inherently differential itself.

Answer: Lypophilization

Lyophilization, also known as freeze-drying, is a method used to preserve perishable materials, including cells, by freezing them and then removing the ice by sublimation under vacuum. This process results in the removal of water from the cells without damaging their structure, allowing them to be stored for long periods without degradation.

The other options are incorrect:

• Pasteurization: This process involves heating a liquid to a specific temperature for a short time to kill harmful bacteria but doesn’t involve dehydration. It’s commonly used for milk and other beverages.
• Dessication: This is a general term for drying or removing water content. While it can be used in some cell preservation techniques, it doesn’t necessarily involve freezing.
• Disinfection: This refers to the process of destroying or inactivating microorganisms. While disinfection might be used in conjunction with cell preservation techniques, it’s not the primary method for dehydrating cells.

Answer: Sterlization

Sterilization is the process of completely eliminating all forms of microbial life, including bacteria, viruses, fungi, and spores, from an object or a surface. It ensures that the item is completely free of viable microorganisms, making it safe for use in sterile environments such as surgical procedures, pharmaceutical manufacturing, and food processing.

The other options are incorrect:

• Disinfection: Disinfection is the process of reducing the number of microorganisms on surfaces or objects to a level considered safe for public health.
• Surgical sterilization: Surgical sterilization typically refers to procedures such as vasectomy or tubal ligation, which are used to permanently prevent reproduction in humans. While these procedures involve sterilization of a specific area of the body.
• Disinfection Sterilization: It combines both disinfection and sterilization, which are distinct processes. Disinfection aims to reduce the number of microorganisms to a safe level, while sterilization aims to completely eliminate all microorganisms.

Answer: Time required to kill all cells at a given temperature

Thermal death time (TDT) refers to the specific amount of time needed to eliminate all viable cells of a particular microorganism at a constant temperature. It’s a crucial concept in various fields like food processing, sterilization procedures, and understanding microbial resistance to heat.

The other options are incorrect:

• Temperature that kills all cells in a given time: This reverses the concept. TDT focuses on the time required at a specific temperature, not the other way around.
• Time and temperature needed to kill all cells: While both time and temperature play a role, TDT specifically refers to the duration needed at a set temperature.
• All of the above: This isn’t entirely accurate. While temperature does influence TDT, TDT focuses on the time aspect at a fixed temperature.

Answer: Complex

Complex media, unlike defined media, have an unknown or undefined composition. They often contain natural ingredients like animal or plant extracts, blood products, or yeast extract. While the exact components might not be precisely known, these media provide a rich source of nutrients for various microorganisms to grow.

The other options are incorrect:

• Simple: Simple media, in contrast to complex media, have a known and defined chemical composition. Each ingredient and its concentration are precisely specified.
• Defined: Defined media is synonymous with simple media, where all the components and their quantities are clearly defined.
• Natural: Natural doesn’t necessarily imply unknown composition. While some natural materials might be used in complex media, the term “complex” specifically refers to the lack of a precisely defined list of ingredients.

Answer: Diophtheria toxin

Elek’s gel diffusion test is a specific immunological assay used to identify and differentiate between various bacterial toxins, particularly diphtheria toxin. The test relies on the principle of antigen-antibody reaction. In this case, the suspected toxin (antigen) diffuses through a gel containing diphtheria antitoxin (antibody).

The other options are incorrect:

• Tetani toxin: While Elek’s gel diffusion test can be adapted to detect other toxins, the standard application focuses on diphtheria toxin identification.
• Cholera toxin: Similar to tetani toxin, the test isn’t typically used for routine cholera toxin detection. There might be variations of the test for other toxins, but diphtheria toxin remains the primary target.
• Toxoid: Toxoids are inactivated toxins used in vaccinations. The Elek’s gel diffusion test aims to detect active toxins produced by bacteria, not the presence of inactivated toxoids.

Answer: Below 100oC

Pasteurization is a heat treatment process for food and beverages that utilizes temperatures below 100°C (212°F) to eliminate harmful bacteria and extend shelf life. It’s a critical step in ensuring food safety without significantly altering the taste or nutritional value of the product.

The other options are incorrect:

• Above 150oC: This temperature would be closer to sterilization, which is a more extreme process aiming to eliminate all microbial life, not just the targeted pathogens addressed by pasteurization.
• 110oC: While some variations of pasteurization might approach this temperature for very short durations, typically pasteurization occurs below 100°C.

Answer: Isolation

Isolation refers to the process of obtaining a single, pure culture of bacteria from a mixed population. This typically involves techniques like streak plating, where a diluted sample is spread across a nutrient agar plate to achieve well-separated colonies. Picking a single, well-isolated colony ensures that further analysis or experiments are conducted on a population derived from a single bacterial cell.

The other options are incorrect:

• Separation: While separation is a general term for dividing things, isolation in microbiology specifically refers to obtaining a pure culture, not just any kind of separation.
• Pure culturing: This is the desired outcome of isolation. Pure culturing refers to a population derived from a single bacterial cell, but it’s not the process itself.
• All of these: While isolation does involve separation and ultimately leads to a pure culture, it’s the specific term used for obtaining a single colony from a mixed population.

Answer: Drying

Drying, while effective in reducing microbial activity, doesn’t necessarily kill spores. Spores are dormant stages of bacteria that are highly resistant to harsh environmental conditions, including drying. They can remain viable for extended periods and germinate when favorable conditions return.

The other options are incorrect:

• Hot air oven: Hot air ovens utilizing high temperatures (typically above 160°C) can effectively kill most bacteria and spores with sufficient exposure time.
• Autoclave: Autoclaves are pressure cookers that use steam under high pressure and temperature (usually around 121°C) to achieve sterilization. This intense environment is highly effective in eliminating all forms of microbial life, including spores.

Answer: Dark field microscope

Treponema pallidum, the bacterium responsible for syphilis, is best identified using a dark field microscope. Dark field microscopy utilizes a special illumination technique where the specimen appears bright against a dark background. This technique enhances the visibility of thin, spiral-shaped organisms like Treponema pallidum, which are difficult to observe under conventional bright field microscopy.

The other options are incorrect:

• Bright field microscope: Bright-field microscopy uses direct light illumination, making it unsuitable for visualizing T. pallidum due to its pale and thin structure.
• Fluorescence microscope (listed twice): Fluorescence microscopy requires the specimen to be labeled with fluorescent dyes, which isn’t typically used for routine T. pallidum identification. While there might be some research applications using fluorescence, dark-field microscopy remains the standard method.

Answer: 120oC

Autoclaving is a sterilization method that involves heating materials or equipment with steam under pressure. Typically, autoclaving is carried out at a temperature of 120°C (250°F) or higher, depending on the specific requirements of the materials being sterilized. The combination of high temperature and pressure ensures effective sterilization by killing or inactivating microorganisms, including bacterial spores.

The other options are incorrect:

• Dry heat: Autoclaving involves the use of steam, rather than dry heat, for sterilization. Dry heat sterilization typically requires higher temperatures and longer exposure times compared to autoclaving.
• Atmospheric pressure: Autoclaving is carried out under pressure, typically at 15 psi (pounds per square inch) above atmospheric pressure. This elevated pressure helps to increase the boiling point of water and allows for the effective penetration of steam into materials, enhancing the sterilization process.
• All of these: While autoclaving involves the application of heat, pressure, and steam, it is not typically carried out at atmospheric pressure. Autoclaving requires elevated pressure to ensure effective sterilization.

Answer: 62.8oC

Pasteurization is a process of heat treatment used to reduce the number of pathogenic microorganisms in food and beverages. The most common temperature used in pasteurization is 62.8°C (145°F) for a specific time, which varies depending on the product and desired level of microbial reduction. This temperature is sufficient to kill many harmful bacteria while preserving the flavor and nutritional quality of the product.

The other options are incorrect:

• 35.7°C (96.3°F): This temperature is too low to be effective for pasteurization. Pasteurization temperatures need to be high enough to eliminate harmful bacteria.
• 60.8°C (141.4°F): This temperature might be on the lower end of the pasteurization range, but it’s possible that some LTL pasteurization processes might use temperatures close to this. It’s generally recommended to stay above 62.8°C for assured pasteurization.
• 68.2°C (155°F): This is within the typical pasteurization temperature range.

Answer: Inoculum

An inoculum refers to a small amount of a culture (containing microorganisms) that is introduced into a fresh, sterile medium to initiate its growth. In the context of a pure culture method, the inoculum would be a sample containing only the desired bacterial species, isolated from a potentially mixed population.

The other options are incorrect:

• Suspension: While a bacterial culture can be prepared as a suspension in a liquid medium, “suspension” is a more general term and doesn’t necessarily imply a pure culture.
• Dilution: Dilution often involves taking a small sample from a culture and mixing it with a larger volume of sterile diluent. This might be a step used to prepare the inoculum for a pure culture method, but dilution itself isn’t the final product (the inoculum).

Answer: All of these

Algae are a diverse group of photosynthetic organisms that offer a wealth of nutritional benefits. They are a concentrated source of various essential nutrients, including:

• Carbohydrates: Algae can store energy in the form of carbohydrates like starches and sugars. The specific type and amount of carbohydrates vary depending on the algae species.
• Proteins: Algae are a good source of high-quality protein, containing all the essential amino acids needed by the human body. Some algae species even have a higher protein content than meat.
• Vitamins: Algae are rich in a variety of vitamins, including vitamins A, B complex (especially B12), C, D, and E. This makes them a valuable dietary source of these essential micronutrients.

Answer: Corynebacterium glutamicum

Corynebacterium glutamicum is a non-pathogenic bacterium commonly used for industrial production of various amino acids, including L-lysine. This bacterium can efficiently ferment sugars and convert them into L-lysine through metabolic processes.

The other options are incorrect:

• Clostridium botulinum: This bacterium is known for producing a potent neurotoxin responsible for botulism. It’s not typically used for L-lysine production due to its safety concerns.
• Mycobacterium sps: Mycobacteria are a diverse group, some of which are pathogenic (causing diseases like tuberculosis). While some species might have metabolic pathways for L-lysine synthesis, they aren’t commonly used for industrial production.
• Pseudomonas: Similar to Mycobacterium sps, some Pseudomonas species might be able to synthesize L-lysine, but Corynebacterium glutamicum is the preferred choice for industrial production due to its efficiency and safety profile.

Answer: Growth

Growth refers to the orderly increase in size and mass of a cell. This involves the synthesis of new cellular components, including proteins, lipids, carbohydrates, and nucleic acids. As these components are produced, the cell enlarges and becomes more complex. Growth is a fundamental characteristic of living cells and is essential for the development and maintenance of an organism.

The other options are incorrect:

• Reproduction: Reproduction is the process by which an organism creates new individuals. While growth often precedes reproduction, they are distinct processes. Growth can occur without reproduction (e.g., bacterial growth before cell division).
• Binary fission: Binary fission is a specific type of cell division in prokaryotes (bacteria) where a single cell replicates to form two identical daughter cells. It’s a mechanism for reproduction, but growth can occur without binary fission (e.g., some cells grow in size before dividing).

Answer: 1.0

Thiobacillus thiooxidans is a type of bacteria known for its ability to oxidize sulfur compounds. It is an extremophile that thrives in extremely acidic environments, typically growing at a pH near 1.0. These bacteria play a role in the sulfur cycle, contributing to the oxidation of sulfur compounds in environments such as acid mine drainage.

The other options are incorrect:

• 7.0: This pH value represents neutral conditions, which are not conducive to the growth of Thiobacillus thiooxidans, an acidophilic bacterium.
• 6.0: While this pH value is acidic, it is still not as extreme as the pH at which Thiobacillus thiooxidans typically grows. These bacteria prefer even lower pH levels.
• 9.5: This pH value represents alkaline conditions, which are not suitable for the growth of Thiobacillus thiooxidans, an acidophilic bacterium.

Answer: Tindalisation

Tindalisation is a method of discontinuous heating used for sterilization. It involves repeated cycles of heating a liquid to a moderate temperature (typically around 56°C) for a specific duration, followed by incubation at room temperature for a period (allowing for spore germination). This cycle is repeated multiple times (often three times) to ensure the destruction of heat-resistant bacterial spores.

The other options are incorrect:

• Pasteurization: Pasteurization is a single-step heat treatment process typically used for milk and other beverages. It employs lower temperatures compared to tindalisation and aims to eliminate harmful bacteria but not necessarily all spores.
• Sterilization: Sterilization refers to the complete elimination of all microbial life forms, including bacteria, viruses, and spores. Tindalisation is one method used for sterilization, but it’s not the only one. Other methods like autoclaving achieve sterilization in a single step.
• Fermentation: Fermentation is a biological process where microorganisms convert carbohydrates into other products like alcohols, acids, or gases. It doesn’t involve heating and isn’t a method for sterilization.

Answer: Separation of a single colony

Isolation refers to the process of obtaining a pure culture of a specific microorganism from a mixed population. This typically involves techniques like streak plating, where a diluted sample is spread across a nutrient agar plate to achieve well-separated colonies. Picking a single, well-isolated colony ensures that further analysis or experiments are conducted on a population derived from a single bacterial cell.

The other options are incorrect:

• Purification of culture: While obtaining a pure culture is the desired outcome of isolation, “isolation” itself refers to the specific technique of separating a single colony.
• Introduction of inoculum: An inoculum is a small amount of a culture containing microorganisms used to initiate growth in a fresh medium. Inoculation is a separate step that often follows successful isolation of a single colony.
• To grow microorganisms on surfaces: While growing microorganisms often involves using surfaces like agar plates, this is a broader concept. Isolation specifically focuses on obtaining a pure culture from a mixed population.

Answer: 121oC temp.and 15 lbs. pressure for 20 min.

Autoclaving is a method of sterilization that utilizes steam under pressure to kill microorganisms. The conditions typically required for autoclaving include a temperature of 121°C (250°F) and a pressure of 15 pounds per square inch (psi) for about 20 minutes. These parameters ensure effective sterilization of the materials being processed.

The other options are incorrect:

• 120°C temperature and 20 lbs. pressure for 30 minutes: While close, a slightly higher temperature (121°C) is generally recommended for reliable sterilization. The time (20 minutes) might be sufficient at 121°C.
• 150°C temperature for 1 hour: While a higher temperature can theoretically achieve sterilization faster, such extreme conditions might damage heat-sensitive materials often sterilized in autoclaves. The standard settings provide a balance between effectiveness and safety for various materials.
• 130°C temperature for 2 hours: Similar to the 150°C option, this setting uses a higher temperature but for a longer duration. Standard autoclaving conditions (121°C for 20 minutes) are generally preferred for most applications.

Answer: Gram positive bacteria

Lysozyme is an enzyme found in various bodily fluids (tears, saliva, mucus) and some white blood cells. It works by hydrolyzing (breaking down) peptidoglycan, a major component of the cell wall in gram-positive bacteria. This disrupts the cell wall integrity, leading to the death of the bacteria.

The other options are incorrect:

• Gram negative bacteria: The outer membrane of gram-negative bacteria provides an additional barrier that can limit the effectiveness of lysozyme. While lysozyme might have some activity against some gram-negative strains, it’s generally more effective against gram-positive bacteria.
• Protozoa: Lysozyme doesn’t have a significant effect on protozoa, which are single-celled eukaryotes with different cell wall structures compared to bacteria.
• Helminthes: Helminthes are parasitic worms with complex body structures. Lysozyme wouldn’t be effective against them.

Answer: Differential medium

Blood agar medium is a type of solid growth medium used in microbiology to culture a wide variety of microorganisms, particularly fastidious bacteria such as Streptococcus species. It is called a differential medium because it contains blood, usually sheep or horse blood, which allows for the differentiation of microorganisms based on their hemolytic activity. Hemolysis can result in distinct patterns on the agar, aiding in the identification of certain bacteria.

The other options are incorrect:

• Enrichment medium: Blood agar is considered enriched because of the added blood, but enrichment is a broader concept. Blood agar has the additional functionality of differentiating bacteria based on hemolysis.
• Selective medium: Selective media are designed to favor the growth of specific types of bacteria by containing ingredients that inhibit the growth of others. Blood agar doesn’t specifically inhibit any bacterial type, it allows growth of a wide range but differentiates them based on hemolysis.

Answer: Dry heat

Infrared radiation is a method of sterilization that utilizes heat generated by infrared rays to kill microorganisms. It is considered a form of dry heat sterilization because it does not involve the use of moisture or steam. Instead, it relies on the direct transfer of heat energy to the material being sterilized.

The other options are incorrect:

• Moist heat: Moist heat sterilization utilizes steam or boiling water to achieve sterilization. IR radiation doesn’t involve moisture.
• Chemical method: Chemical sterilization methods rely on disinfecting chemicals to kill microorganisms. IR radiation uses a physical method (heat) for sterilization.
• Mechanical method: Mechanical sterilization methods involve physical removal or filtration of microorganisms. IR radiation utilizes heat to kill them, not physically remove them.

Answer: Freeze-drying

Lyophilization is a process for removing water from a product by freezing it and then lowering the pressure so that the ice can sublimate directly into vapor, bypassing the liquid phase. This technique is particularly useful for preserving perishable items like food and medicine because it minimizes damage caused by high heat.

The other options are incorrect:

• Sterilization: While lyophilization can sometimes extend the shelf life of products and reduce the risk of microbial growth, it’s not a guaranteed sterilization method. Sterilization eliminates all forms of microbial life, which lyophilization may not achieve.
• Burning to ashes: This is the complete opposite of lyophilization. Burning involves applying high heat to a material, which destroys it and leaves behind ashes. Lyophilization, on the other hand, uses low temperatures and aims to preserve the structure of the material.
• Exposure to formation: This option is unclear and doesn’t relate to water removal techniques. It’s possible you meant “exposure to radiation,” which wouldn’t be the same as lyophilization either. Radiation can sterilize materials but wouldn’t remove water in the same way.

Answer: 160oC for 1 hour

The most common sterilization temperature used in hot air ovens is 160°C for 1 hour. This setting effectively eliminates most bacteria and spores.

The other options are incorrect:

• 100°C for 1 hour: This temperature might not be sufficient for sterilization in all cases. Some bacteria and spores can survive at 100°C.
• 120°C for 1 hour: While this temperature increases the success rate of sterilization compared to 100°C, it might still not be effective for highly resistant organisms.
• 60°C for 1 hour: This temperature is too low for sterilization purposes. It might be suitable for drying materials but wouldn’t eliminate microorganisms.

Answer: Efficiency of a disinfectant

The phenol coefficient is a historical method for comparing the disinfecting power of a substance to phenol (carbolic acid). It indicates how much more or less diluted a disinfectant needs to be compared to phenol to achieve the same level of killing against specific microorganisms under controlled test conditions.

The other options are incorrect:

• Dilution of a disinfectant: While the phenol coefficient is related to dilution, it’s not a direct measure. It represents the relative potency, not the recommended dilution for practical use.
• Purity of a disinfectant: The phenol coefficient doesn’t necessarily reflect the purity of a disinfectant. It focuses on the effectiveness against microbes, not the presence of impurities.
• Quantity of a disinfectant: Phenol coefficient doesn’t tell you the recommended amount of disinfectant to use. It’s a ratio based on a specific test, and actual usage depends on factors like type of organism, surface type, and contact time.

Answer: Standard Plate Count (SPC)

Standard Plate Count (SPC) is an agar plate method commonly used to estimate the total number of viable aerobic bacteria present in milk. It involves diluting a milk sample and plating it on a specific agar medium, followed by incubation and colony counting.

The other options are incorrect:

• Spread plate: While spread plate is also an agar plate method, it’s a general technique used for isolating and identifying different bacterial colonies from a mixed culture. It’s not specifically designed for estimating bacterial numbers in milk.
• Lawn culture: Similar to spread plate, lawn culture is an agar plate method for isolating individual colonies. However, it aims for a dense, even distribution of colonies across the entire plate, making it less suitable for accurate bacterial count in a sample like milk.
• Roll tube method: This method utilizes a liquid broth medium in a test tube that’s solidified by tilting during incubation. It’s not commonly used for milk analysis because SPC requires plating on a solid agar surface for easy colony counting.

Answer: Red algae

Agar is a jelly-like substance primarily obtained from the cell walls of specific red algae species. The most common sources are “ogonori” (Gracilaria) and “tengusa” (Gelidium) belonging to the Rhodophyta (red algae) phylum.

The other options are incorrect:

• Brown algae: While brown algae have various industrial uses, they are not a source of agar. Brown algae contain different polysaccharides like alginic acid.
• Green algae: Similar to brown algae, green algae don’t contain agar. They have their own cell wall structures composed of cellulose and other carbohydrates.
• Blue-green algae: Blue-green algae (also known as cyanobacteria) are actually not algae but a type of bacteria. They wouldn’t possess the same cell wall components as red algae and wouldn’t be a source of agar.