MicroBiology MCQs with Answer and Explnation | Chapter 58

Answer: Soil enriched with bird excrement

The symptoms, along with the granulomatous inflammation and macrophages containing oval structures, are indicative of coccidioidomycosis, commonly known as Valley fever. The fungus responsible for this infection, Coccidioides species, resides in the soil, particularly in areas with bird excrement enrichment. Inhalation of spores from contaminated soil leads to infection.

The other options are incorrect:

• Contaminated drinking water: This option is incorrect because coccidioidomycosis is not transmitted through water. It is primarily acquired through inhalation of fungal spores from the environment.
• Cat feces: Cat feces are associated with the parasite Toxoplasma gondii, which can cause toxoplasmosis. However, the symptoms described in the scenario, along with the findings of granulomatous inflammation and oval structures, are not consistent with toxoplasmosis.
• Another human via respiratory secretions: This option is incorrect because coccidioidomycosis is not transmitted directly from person to person via respiratory secretions. It is an environmental fungal infection acquired through inhalation of spores.

Answer: B. dermatitidis infection is commonly diagnosed by serologic tests because it does not grow in culture.

Blastomyces dermatitidis actually grows well in culture under specific conditions. Culturing the fungus from patient samples is a crucial diagnostic tool for blastomycosis.

The other options are incorrect:

• B. dermatitidis causes granulomatous skin lesions. – This statement is correct. Blastomycosis can cause skin lesions with a granulomatous inflammatory pattern.
• B. dermatitidis grows as a mold in the soil in North America. – This statement is also correct. Blastomyces dermatitidis exists as a mold in the environment, particularly in North American soil.
• B. dermatitidis is a dimorphic fungus that forms yeast cells in tissue. – This statement is accurate. Blastomyces dermatitidis exhibits dimorphism, meaning it transforms from a mold in the environment to a yeast form within human tissue.

Answer: Pneumocystis jiroveci

Given the clinical presentation of a 42-year-old man with AIDS experiencing dyspnea, dry cough, fatigue, low-grade fever, and bilateral symmetrical interstitial and alveolar infiltration on chest x-ray, the most likely cause is Pneumocystis jiroveci pneumonia (PCP). PCP is a common opportunistic infection in individuals with compromised immune systems, such as those with AIDS.

The other options are incorrect:

• Histoplasma capsulatum: While Histoplasma can cause lung infections, it’s less common as an opportunistic infection in AIDS compared to Pneumocystis jiroveci.
• Cryptococcus neoformans: This fungus can cause meningitis in immunocompromised patients, but the respiratory symptoms and chest x-ray findings are not typical of Cryptococcus infection.
• Cryptosporidium parvum: This parasite primarily causes gastrointestinal illness, not the respiratory symptoms seen in this case.

Answer: Sporothrix

Sporothrix is less commonly found as a colonizer compared to the other listed fungi. While it can occasionally occur in open wounds, Sporothrix typically causes its own distinct infection (sporotrichosis) rather than simply colonizing an existing lesion.

The other options are incorrect:

• Aspergillus: Aspergillus is a very common fungus and can readily colonize or even cause infections in wounds, sinuses, and lungs.
• Candida: Candida is another highly prevalent fungus that frequently colonizes various body surfaces, including the skin, mucous membranes, and the gastrointestinal tract.
• Mucor: Mucor is an opportunistic fungus that can take advantage of compromised tissues and establish itself as a colonizer, especially in diabetic patients with uncontrolled blood sugar.

Answer: Bacteria

Mitochondria are membrane-bound organelles found in eukaryotic cells, responsible for generating energy in the form of ATP through aerobic respiration. Bacteria are prokaryotic organisms and lack membrane-bound organelles such as mitochondria. Instead, bacteria generate energy through various metabolic pathways within their cytoplasm.

The other options are incorrect:

• Filamentous fungi: These are eukaryotic organisms and possess mitochondria for cellular respiration.
• Cestodes: As eukaryotes, cestodes also have mitochondria to meet their energy needs.
• Protozoan parasites: These single-celled eukaryotes typically have mitochondria for energy production.

Answer: Human and fungal cells have similar robosomes, whereas bacterial ribosomes are different

Ribosomes are cellular organelles responsible for protein synthesis. Both human and fungal cells are eukaryotic, and they possess structurally and functionally similar ribosomes, consisting of large and small subunits. In contrast, bacterial ribosomes are structurally and functionally different, comprising smaller subunits. This difference in ribosome structure is utilized in antibiotic therapy, as antibiotics can selectively target bacterial ribosomes without affecting eukaryotic ribosomes.

Incorrect options:

• Human and bacterial cells have plasmids, whereas fungal cells do not: Plasmids are small, circular DNA molecules found in bacteria and some eukaryotic organisms, such as yeast. While bacterial cells commonly contain plasmids, fungal cells can also harbor plasmids. Therefore, this statement is not accurate.
• Human and fungal cells have a similar cell wall, in contrast to bacteria, whose cell wall contains peptidoglycan: This statement is inaccurate. Bacterial cell walls typically contain peptidoglycan, a unique polymer absent in human and fungal cell walls. While fungal cell walls contain other components such as chitin, they do not have peptidoglycan. Human cells lack a cell wall altogether, being surrounded only by a plasma membrane.
• Human and fungal cells have similar ribosomes, whereas bacterial ribosomes are different: This statement is the most accurate among the options provided, as explained in the correct answer.

Answer: Their survival ability is based on their enhanced metabolic activity

Bacterial spores, such as those produced by certain species of Bacillus and Clostridium, are highly resistant structures formed by some gram-positive rods. Their survival ability is not based on enhanced metabolic activity but rather on their highly resistant coat and low metabolic activity. Spores can survive extreme conditions, including heat, desiccation, and chemical exposure, due to their low water content and protective coat.

The other options are incorrect:

• They are formed by gram-positive rods: While spore formation is more common in gram-positive bacteria, some gram-negative bacteria can also form spores.They can be killed by being heated to 121oC for 15 minutes: This process, known as autoclaving, is a common method for sterilizing equipment and killing bacterial spores due to its effectiveness.They contain much less water than bacterial cells: This statement is accurate. Spores have a dehydrated cytoplasm with much less water compared to vegetative bacterial cells.

Answer: Causes the release of tumor necrosis factor

Endotoxin, a component of the outer membrane of gram-negative bacteria, binds to specific receptors on immune cells. This binding triggers a cascade of events, including the release of pro-inflammatory cytokines like TNF. TNF plays a central role in the inflammatory response caused by endotoxins.

The other options are incorrect:

• Degrades lecithin in cell membranes: While endotoxins can disrupt cell membranes, their primary mode of action is not through direct degradation of lecithin.
• Blocks release of acetylcholine: Endotoxins primarily affect immune cells and don’t directly target the nervous system, where acetylcholine is a key neurotransmitter.
• Inactivates elongation factor 2: Elongation factor 2 is important for protein synthesis, and its inactivation wouldn’t be the primary mechanism by which endotoxins trigger inflammation.

Answer: Possession of pili

Pili are hair-like structures on bacteria that help them adhere to surfaces, including catheters. In this scenario, the presence of pili on the contaminating bacteria likely facilitated their attachment to the catheter, leading to blockage and subsequent infection.

The other options are incorrect:

• Possession of IgA protease: IgA protease is an enzyme produced by some bacteria that can degrade IgA, an antibody found in mucus. While this could contribute to immune evasion, it wouldn’t directly lead to catheter blockage.
• Peptidoglycan layer: Peptidoglycan is a rigid layer in the bacterial cell wall, essential for maintaining bacterial shape. It’s not directly involved in catheter adherence.
• Ergosterol containing membrane: Ergosterol is a sterol found in the membranes of fungi, not bacteria. The contaminating organism in this case is most likely a bacterium.

Answer: Spores are formed primarily by organisms of the genus Neisseria

Neisseria, which includes species like Neisseria gonorrhoeae (causing gonorrhea) and Neisseria meningitidis (causing meningitis), do not form spores. Spore formation is a characteristic of some bacteria, primarily within the phylum Bacillota (formerly Firmicutes), which includes Bacillus and Clostridium species.

The other options are incorrect:

• Spores are resistant to boiling: Bacterial spores are highly resistant to harsh environments, including boiling temperatures for extended periods.
• Spores are metabolically inactive and contain dipicolinic acid, a calcium chelator: This statement is accurate. Spores are dormant and contain dipicolinic acid, which helps them withstand harsh conditions.
• Spores are formed under adverse environmental conditions such as the absence of a carbon source: This statement is also accurate. Spore formation is often triggered by unfavorable conditions like nutrient depletion or extreme temperatures, allowing the bacteria to survive until a more suitable environment returns.

Answer: Adverse environmental stress

Endospore formation is a survival mechanism for bacteria. When they encounter harsh conditions like lack of nutrients, extreme temperatures, desiccation (drying out), or UV radiation, they can transform into dormant endospores. These spores are highly resistant and can stay viable for extended periods until the environment becomes favorable again.

The other options are incorrect:

• Nutrient surplus: Abundant nutrients typically promote bacterial growth and reproduction, not spore formation.
• Colony formation: Colony formation simply refers to a visible cluster of bacteria growing on a surface. It’s not directly linked to spore formation.
• Need for reproduction: Endospores are not reproductive structures. They are dormant forms that allow the bacteria to survive, not reproduce, during unfavorable conditions.

Answer: They bind to specific cells receptors whereas exotoxins do not

Both endotoxins and exotoxins can interact with host cells, but their mechanisms differ. Endotoxins interact with toll-like receptors (TLRs), which are present on various immune cells. This interaction triggers a broad inflammatory response. In contrast, exotoxins often have more specific targets and bind to specific receptors on host cells. This targeted binding allows them to exert more defined effects, like disrupting cellular processes or causing tissue damage.

The other options are incorrect:

• They are part of the bacterial cell wall, whereas exotoxins are not: This statement is accurate. Endotoxins are lipopolysaccharides (LPS) found in the outer membrane of gram-negative bacteria. Exotoxins are secreted proteins produced by various bacteria, gram-positive and gram-negative.
• They are less potent (ie, less active on a weight basis) than exotoxins: While some exotoxins are indeed highly potent, endotoxins can also cause significant inflammatory responses, depending on the dose and the host’s immune system.
• They are more stable on heating than exotoxins: This statement is generally true. Endotoxins, due to their LPS structure, are more heat-stable compared to exotoxins, which are proteins and can be denatured by heat.

Answer: Sulfonamides affect folic acid synthesis in bacteria, a pathway that does not occur in human cells.

Isoniazid inhibits the synthesis of mycolic acids in the cell wall of mycobacteria, such as Mycobacterium tuberculosis, by inhibiting the enzyme enoyl-ACP reductase (InhA). It does not directly affect DNA polymerase.

The other options are incorrect:

• Penicillins affect bacteria rather than human cells because bacteria have a cell wall, whereas human cells do not: This statement is correct. Penicillins exert their bactericidal effect by inhibiting the synthesis of peptidoglycan, a component of the bacterial cell wall. Human cells do not have a peptidoglycan cell wall, so penicillins are selective for bacteria.
• Sulfonamides affect folic acid synthesis in bacteria, a pathway that does not occur in human cells: This statement is correct. Sulfonamides inhibit the enzyme dihydropteroate synthase, which is involved in the synthesis of folic acid in bacteria. Human cells do not synthesize folic acid de novo; they obtain it from the diet. Therefore, sulfonamides selectively target bacterial cells.
• Chloramphenicol affects the large subunit of the bacterial ribosome, which is different from the large subunit of the human ribosome: This statement is correct. Chloramphenicol binds to the 50S subunit of the bacterial ribosome, inhibiting protein synthesis. While the structure of bacterial and human ribosomes is similar, there are enough differences in the structure of the large subunit to allow chloramphenicol to selectively bind to bacterial ribosomes.

Answer: Peptidoglycan

Peptidoglycan is a rigid layer in the bacterial cell wall of gram-positive bacteria, including the most likely culprit in this case – Streptococcus pyogenes (group A Streptococcus), the cause of strep throat. Peptidoglycan provides structural support and shape to the cell and protects it from bursting due to osmotic pressure differences between the inside and outside of the bacterium.

The other options are incorrect:

• Lipopolysaccharide (LPS): LPS is a major component of the outer membrane of gram-negative bacteria, not gram-positive bacteria like Streptococcus pyogenes.
• Polysaccharide: While bacteria can have various polysaccharides in their capsules or cell walls, peptidoglycan is the key structural component responsible for osmotic protection in this scenario.
• Phospholipids: Phospholipids are a major component of cell membranes in both bacteria and humans. They contribute to membrane fluidity but are not the primary structure for osmotic protection.

Answer: Opsonization

Opsonization is the process of coating a pathogen with molecules (opsonins) that enhance its recognition and phagocytosis by immune cells. Endotoxins, however, trigger a cascade of inflammatory responses but don’t directly participate in opsonization.

The other options are incorrect:

• Activation of the coagulation cascade: Endotoxins can activate the coagulation cascade, leading to blood clot formation, which can contribute to complications during sepsis.
• Fever: Fever is a common response triggered by endotoxins to enhance immune function.
• Hypotension: Endotoxins can cause vasodilation and increased vascular permeability, leading to a drop in blood pressure (hypotension).

Answer: Peptidoglycan

Peptidoglycan is a rigid structural component of the bacterial cell wall, essential for maintaining shape and osmotic pressure. While it plays a crucial role in bacterial survival, it’s generally not considered to be highly variable and doesn’t contribute significantly to antigenic diversity.

The other options are incorrect:

• Flagella: Flagella are hair-like structures that some bacteria use for motility. They can have different types of flagellin proteins, leading to variations that the immune system can recognize as different antigens.
• Pili: Pili are shorter appendages on some bacteria that help with attachment to surfaces or other cells. They can also have variations in their pilin subunits, contributing to antigenic diversity.
• Capsules: Capsules are polysaccharide layers surrounding some bacteria. These capsules can vary significantly in structure and composition, making them effective shields against the immune system and contributing to antigenic diversity.

Answer: Scanning electron microscopy

SEM uses a focused beam of electrons to scan the surface of a specimen. The interaction between the electrons and the sample generates signals that are used to create a high-resolution, three-dimensional image of the surface topography. This technique is ideal for visualizing the external features of bacterial cells.

The other options are incorrect:

• Transmission electron microscopy (TEM): While TEM can provide high-resolution images of internal structures, it requires slicing the sample very thin. This process doesn’t inherently generate a 3D image. However, by taking images of serial sections, a 3D reconstruction can be built computationally.
• Dark-field microscopy: This technique uses scattered light to illuminate unstained samples, making them appear bright against a dark background. While it can provide good contrast for visualizing some bacterial features, it doesn’t generate a 3D image.
• Fluorescent microscopy: This technique relies on fluorescent molecules attached to specific targets within the cell. It can be used to visualize internal structures in 2D but doesn’t directly provide 3D information.

Answer: Bacterial flagella are nonantigenic in humans because they closely resemble human flagella in chemical composition

Bacterial flagella are antigenic structures, meaning they can elicit an immune response in the host organism. However, they are not antigenic because they resemble human flagella. Instead, they are antigenic due to their unique composition and structure, which are recognized by the host immune system as foreign.

The other options are incorrect:

• Pili mediate the interaction of bacteria with mucosal epithelium: Pili, also known as fimbriae, are hair-like appendages found on the surface of some bacteria. They facilitate bacterial adhesion to host cells and surfaces, including mucosal epithelium, which is important for colonization and infection.
• Polysaccharide capsules retard phagocytosis: Polysaccharide capsules are outermost layers surrounding some bacteria, providing protection against phagocytosis by host immune cells. Capsules inhibit the binding of opsonins, preventing recognition and engulfment by phagocytes.
• Both gram-negative rods and cocci have lipopolysaccharide “endotoxin” in their cell wall: Lipopolysaccharide (LPS), also known as endotoxin, is a component of the outer membrane of Gram-negative bacteria, including both rods and cocci. LPS plays a role in bacterial pathogenesis and can induce inflammatory responses in the host organism.

Answer: Some exotoxins contain lipopolysaccharides as the toxic components

Lipopolysaccharides (LPS) are endotoxins, a specific type of toxin found in the outer membrane of gram-negative bacteria. Exotoxins, on the other hand, are diverse proteins secreted by various bacteria, gram-positive and gram-negative. They don’t inherently contain LPS as their toxic component.

The other options are incorrect:

• When treated chemically, some exotoxins lose their toxicity and can be used as immunogens in vaccines: This statement is accurate. By inactivating the toxic properties of certain exotoxins, they can be safely used in vaccines to stimulate the immune system to develop antibodies against the toxin, providing protection against the disease.
• Some exotoxins are capable of causing disease in purified form, free of any bacteria: This statement is accurate. Exotoxins are potent toxins that can exert their harmful effects even when isolated from the bacteria that produce them.
• Some exotoxins act in the gastrointestinal tract to cause diarrhea: This statement is accurate. Many bacterial toxins, including some exotoxins, target the gastrointestinal tract leading to symptoms like diarrhea.

Answer: Some mycoplasmas contain pentaglycine in their peptidoglycan

Mycoplasmas lack a cell wall altogether, hence they do not contain peptidoglycan, and thus do not contain pentaglycine in their peptidoglycan.

The other options are incorrect:

• Gram-positive cocci containing teichoic acid: Teichoic acid is a component found in the cell wall of Gram-positive bacteria, serving various functions such as cell wall maintenance and as an antigen. This statement is correct.
• Gram-negative rods containing lipid A: Lipid A is a component of lipopolysaccharide (LPS) found in the outer membrane of Gram-negative bacteria, such as rods. This statement is correct.
• Gram-positive rods containing dipicolinic acid in their spores: Dipicolinic acid is a major component of the spores of Gram-positive bacteria, particularly in Bacillus and Clostridium species. This statement is correct.

Answer: Negative staining

Negative staining is a simple and rapid technique used to visualize the overall morphology (shape and size) of bacteria, including any capsules present. It works by staining the background dark, leaving the unstained, transparent capsule as a clear halo around the stained bacterial cell.

The other options are incorrect:

• Scanning electron microscopy (SEM): SEM is a powerful tool for viewing the detailed surface features of bacteria at high magnification. However, it requires complex sample preparation and doesn’t provide information about the capsular material itself.
• Ziehl-Neelsen staining: This staining method is specifically used to identify acid-fast bacteria like Mycobacterium tuberculosis. It wouldn’t be used to visualize capsules.
• Gram staining: This is a common method for classifying bacteria into two broad groups based on their cell wall structure. While Gram staining can differentiate between gram-positive and gram-negative bacteria, which can sometimes be associated with capsule presence, it doesn’t directly visualize the capsule itself.

Answer: Outer Membrane

The outer membrane of gram-negative bacteria is the primary culprit in triggering gram-negative shock. This membrane contains a molecule called lipopolysaccharide (LPS), specifically the lipid A portion of LPS. When gram-negative bacteria die or are lysed (broken open) by the immune system, LPS is released and interacts with immune cells, triggering a cascade of inflammatory responses that can lead to gram-negative shock.

The other options are incorrect:

• Capsule: While capsules can contribute to virulence by protecting bacteria from phagocytosis (engulfment by immune cells), they are not directly responsible for triggering gram-negative shock.
• Periplasmic space: This space between the inner and outer membrane plays a role in some bacterial processes, but it’s not directly involved in triggering gram-negative shock.
• Peptidoglycan-teichoic acid fragments: These components are more associated with gram-positive bacteria and wouldn’t be the primary trigger for gram-negative shock.

Answer: Facultative anaerobe

This type of organism can survive and generate energy with or without oxygen. When oxygen is present, they prefer to use aerobic respiration, which is a more efficient process for ATP (energy) production. However, when oxygen is limited, they can switch to fermentation, a less efficient but still functional way to produce ATP.

The other options are incorrect:

• Aerobe: Obligate aerobes strictly require oxygen for respiration and cannot survive or grow in its absence.
• Anaerobe: Obligate anaerobes are poisoned by oxygen and can only survive and grow in environments without oxygen.
• Facultative aerobe: This term doesn’t exist. It’s likely a typo of “facultative anaerobe” and would have the same meaning.

Answer: All the above

• He is known as the father of bacteriology (alongside Louis Pasteur): Robert Koch is a pivotal figure in the field of microbiology. He made significant contributions through his discoveries of causative agents for diseases like anthrax, tuberculosis, and cholera. His development of Koch’s postulates also provided a foundational framework for linking specific microorganisms to specific diseases.
• He discovered the causative organism of cholera, Vibrio cholera: In 1883, Koch successfully isolated and identified Vibrio cholerae as the bacterium responsible for cholera outbreaks.
• He discovered the hypersensitivity phenomenon: While Koch is primarily known for his work in bacteriology, he also made contributions to immunology. He described a phenomenon now known as the tuberculin reaction, where individuals infected with tuberculosis exhibit a delayed hypersensitivity response to tuberculin, a purified protein derivative from Mycobacterium tuberculosis.

Answer: All the above

Louis Pasteur was a French microbiologist who made groundbreaking contributions to various areas of microbiology:

• Techniques of Pasteurization: This process of heat treatment to eliminate pathogens from beverages like milk and wine is one of his most famous inventions. It has significantly improved food safety and shelf life.
• Process of Fermentation: Pasteur elucidated the role of microorganisms in fermentation, a crucial process in food production (e.g., cheese, yogurt, wine, beer)
• Rabies, cholera and anthrax vaccine: Pasteur pioneered the development of vaccines for several diseases, including rabies, chicken cholera, and anthrax. His work laid the foundation for modern vaccinology.

Answer: D. Hansen’s bacilli

Mycobacterium leprae is the bacterium that causes leprosy, also known as Hansen’s disease. This disease was named after Gerhard Armauer Hansen, a Norwegian physician who made significant contributions to our understanding of leprosy.

The other options are incorrect:

• Golden bacilli: This term isn’t specific to Mycobacterium leprae. Some bacteria might have a golden appearance under certain conditions, but it’s not a diagnostic term for this particular bacterium.
• B. Koch’s bacillus: This refers to Mycobacterium tuberculosis, the causative agent of tuberculosis. While both are Mycobacterium species, they are different bacteria responsible for distinct diseases.
• Magical bacilli: This is obviously not a scientific term used in microbiology.

Answer: Koch’s bacillus

Mycobacterium tuberculosis was first identified and isolated by German physician Robert Koch in 1882. In recognition of this discovery, it’s also known as Koch’s bacillus.

The other options are incorrect:

• Golden bacilli: This term can be used for various bacteria with a golden appearance in cultures, but it’s not specific to Mycobacterium tuberculosis.
• Magical bacilli: This is not a scientific term used in microbiology.
• Hansen’s bacilli: This refers to Mycobacterium leprae, the bacterium that causes leprosy, a different disease than tuberculosis.

Answer: Staphylococcus

Staphylococcus is not an acid-fast organism. Acid-fast organisms are those that resist decolorization by acid-alcohol during staining procedures such as the Ziehl-Neelsen or Kinyoun stain. They typically have a high content of mycolic acids in their cell walls, which makes them resistant to the decolorizing agent.

The other options are incorrect:

• Mycobacterium tuberculosis: Mycobacterium tuberculosis is an acid-fast bacterium and is a significant human pathogen causing tuberculosis.
• Nocardia: Nocardia species are acid-fast bacteria that can cause infections in humans, particularly in individuals with compromised immune systems.
• Isospora belli: Isospora belli is a parasite, not a bacterium, and it is acid-fast. It can cause gastrointestinal infections, particularly in immunocompromised individuals.

Answer: Mesosome

Mesosomes are folded invaginations of the plasma membrane found in bacteria. These folds increase the surface area available for cellular processes, including respiration. Respiratory enzymes are embedded within the mesosome membrane, facilitating the electron transport chain, a key step in generating ATP (cellular energy) during respiration.

The other options are incorrect:

• Ribosome: Ribosomes are the sites of protein synthesis in the cell and are not directly involved in respiration.
• Pili: Pili are hair-like structures on the bacterial surface that play a role in attachment, motility, and DNA transfer, not respiration.
• Flagella: Flagella are another type of appendage on some bacteria that function in motility, not respiration.

Answer: All the above

All three statements are true about bacteria:

• Respiration, cell division and sporulation are functions of mesosome in bacteria: The folded membrane structure of the mesosome provides increased surface area for essential cellular processes. It can be involved in:
  • Respiration: Respiratory enzymes are embedded within the mesosome membrane, facilitating the electron transport chain for ATP production.
  • Cell division: The mesosome might play a role in septum (cell wall) formation during bacterial cell division.
  • Sporulation: In some bacteria that form endospores, the mesosome might be involved in providing membranes for the developing spore.
• Capsule in bacteria enables adherence to surfaces and protection against phagocytosis: A capsule is a gelatinous layer external to the cell wall of some bacteria. It can provide:
  • Adherence: The capsule can help bacteria stick to surfaces, which can be beneficial for colonization and nutrient acquisition.
  • Protection against phagocytosis: The capsule can make it more difficult for immune cells like phagocytes to engulf and destroy the bacteria.
• Heterotrophs are the bacteria that are unable to synthesize their own food materials: Heterotrophs are organisms that obtain their organic nutrients from other living organisms or organic matter. Many bacteria fall into this category, requiring pre-formed organic molecules for growth and energy.

Answer: All the above

All the statements regarding cocci are correct.

• Cocci are spherical shaped bacteria: Cocci are indeed spherical shaped bacteria. They can occur in various arrangements, including singles, pairs, chains, clusters, and tetrads.
• Cocci present in chain is known as streptococci: Streptococci are cocci that typically occur in chains. Examples include Streptococcus pyogenes, which causes strep throat.
• Cocci present in the shape of grapes is known as staphylococci: Staphylococci are cocci that typically occur in clusters resembling grapes. Examples include Staphylococcus aureus, a common cause of skin infections.

Answer: Vibrio

Vibrio is a genus of bacteria characterized by their comma-shaped morphology. These bacteria are often found in aquatic environments and some species, like Vibrio cholerae, can cause infectious diseases in humans.

The other options are incorrect:

• Staphylococci and Streptococci: These terms refer to arrangements of spherical cocci-shaped bacteria, not the shape of the individual cell itself.
• Bacillus: Bacillus refers to rod-shaped bacteria, another common bacterial morphology.

Answer: Buffered glycerol saline medium

Buffered glycerol saline medium is the recommended transport medium for stool specimens suspected to contain Vibrio cholerae. This medium helps maintain the viability of the bacteria during transport to the laboratory for further analysis and identification.

The other options are incorrect:

• Venkatraman-Ramakrishnan medium: This medium is not typically used for the transport of stool specimens suspected to contain Vibrio cholerae.
• Nutrient broth: Nutrient broth is a general-purpose medium used for the cultivation of a wide range of microorganisms but is not specifically recommended for the transport of Vibrio cholerae.
• Blood agar: Blood agar is a differential medium primarily used for the cultivation and identification of various pathogenic bacteria, particularly those that hemolyze red blood cells. It is not a suitable transport medium for Vibrio cholerae.

Answer: Chocolate agar

Chocolate agar is an enriched medium that provides additional nutrients for the growth of fastidious (difficult to grow) bacteria. It’s prepared from blood agar, where the red blood cells are lysed (broken open) to release nutrients like heme, which are essential for some bacteria.

The other options are incorrect:

• Selenite F broth: This is a selective enrichment broth used to specifically isolate Salmonella species from stool samples. It inhibits the growth of other bacteria while promoting the growth of Salmonella.
• Peptone water: This is a basic broth containing peptone, a source of amino acids. While it provides some nutrients, it’s not considered an enriched medium as it lacks additional components needed by fastidious bacteria.
• MacConkey agar: This is a differential and selective medium used to differentiate between lactose-fermenting and lactose-non-fermenting bacteria. It’s not specifically enriched for fastidious organisms.

Answer: Disinfection

Disinfection refers to the process of eliminating or inactivating microorganisms. By definition, disinfection hinders microbial growth.

The other options are incorrect:

• Moisture: Water is essential for most microbial processes, including growth and reproduction. Lack of moisture can significantly restrict or prevent microbial growth.
• Darkness: While some bacteria require light for certain processes (photosynthesis), the absence of light generally doesn’t completely inhibit microbial growth. Many bacteria can grow in dark environments.
• Temperature: Temperature plays a crucial role in microbial growth. Each species has a minimum, optimum, and maximum temperature range for growth. Temperatures outside this range can slow down or completely stop microbial growth.

Answer: 1-2%

The agar concentration required to prepare nutrient agar is typically in the range of 1-2%. Nutrient agar is a general-purpose medium used for the cultivation of a wide variety of microorganisms. Agar acts as a solidifying agent, providing a solid surface for bacterial growth.

The other options are incorrect:

• 4-6%: This agar concentration is higher than what is typically used to prepare nutrient agar. Such high concentrations are not commonly used for general-purpose media like nutrient agar and may lead to overly firm or brittle agar.
• 0.25-0.5%: This concentration is lower than what is typically used to prepare nutrient agar. Such low agar concentrations are commonly used for media requiring less solidification, such as semi-solid media for motility tests.
• 0.5-1%: While this range is closer to the correct concentration, it is still lower than what is typically used to prepare nutrient agar. Nutrient agar usually requires a slightly higher agar concentration to ensure solidification of the medium.

Answer: Chromosome

MRSA (Methicillin-resistant Staphylococcus aureus) is mediated due to genetic changes in the chromosome of Staphylococcus aureus bacteria. It results from the acquisition of a gene encoding a modified penicillin-binding protein (PBP2a) through horizontal gene transfer.

The other options are incorrect:

• Plasmid: While antibiotic resistance genes can sometimes be found on plasmids, the resistance in MRSA is primarily mediated by chromosomal genes.
• Transposons: Transposons are genetic elements that can move from one location to another within a genome, carrying antibiotic resistance genes. While transposons can contribute to antibiotic resistance, they are not the primary mechanism for MRSA.

Answer: Acute rheumatic fever

Acute rheumatic fever is a post-streptococcal sequelae. This means it’s a complication that can develop after an untreated or inadequately treated streptococcal infection, such as strep throat (pharyngitis) or impetigo.

The other options are incorrect:

• Cellulitis: Cellulitis is a bacterial skin infection that can be caused by various bacteria, not necessarily Streptococcus pyogenes (group A strep) which is linked to post-streptococcal sequelae.
• Pharyngitis (strep throat): This is the initial streptococcal infection itself, not a sequelae (complication) that arises after the infection.
• Impetigo: Similar to pharyngitis, impetigo is another primary streptococcal skin infection, not a complication arising later.

Answer: Urea breath test

The most accurate method of diagnosing Helicobacter pylori infection is the urea breath test. This non-invasive test involves the ingestion of a urea solution labeled with a radioactive or stable isotope. H. pylori produces the enzyme urease, which breaks down urea into ammonia and carbon dioxide. The presence of labeled carbon dioxide in the breath indicates the presence of H. pylori infection.

The other options are incorrect:

• Culture: While culturing H. pylori from a gastric biopsy can be definitive, it’s less sensitive than UBT. Culturing can be affected by factors like prior antibiotic use and requires specialized conditions and expertise in the lab.
• Biopsy urease test: This test involves taking a tissue sample (biopsy) from the stomach lining and testing it for the presence of the urease enzyme produced by H. pylori. It can be accurate, but it requires an endoscopy procedure, which is invasive.
• Histopathology: This involves examining a biopsy sample under a microscope to look for signs of H. pylori infection and inflammation. While it can provide additional information about the stomach lining, it’s not as specific for H. pylori as UBT.

Answer: Mycobacterium TB

Acid-fast staining is a specific technique used to identify bacteria with waxy cell walls rich in mycolic acids. These characteristics make the cell wall highly resistant to staining procedures. Mycobacterium tuberculosis, the bacteria that causes tuberculosis (TB), is a classic example of an acid-fast organism.

The other options are incorrect:

• Clostridium tetani (Ctetani): This bacterium is responsible for tetanus and does not possess an acid-fast cell wall.
• HIV/AIDS: HIV is a virus, not a bacteria, and acid-fast staining is not used for viral detection.
• Meningococci: These bacteria, Neisseria meningitidis, are gram-negative and do not have the specific cell wall structure for acid-fast staining.

Answer: Sexual

Sexual contact, particularly unprotected anal or vaginal sex, carries the highest risk of HIV transmission. The virus can enter the bloodstream through tears in the mucous membranes of the genitals, rectum, or mouth.

The other options are incorrect:

• Blood Products: In developed countries with rigorous blood screening, the risk of HIV transmission through blood products is extremely low.
• Needle/Syringe Sharing: Sharing needles and syringes contaminated with HIV-infected blood is a significant risk factor, particularly among people who inject drugs.
• Mother to Fetus (Perinatal Transmission): While possible, with proper prenatal care and medication, the risk of HIV transmission from mother to fetus during pregnancy, childbirth, or breastfeeding can be significantly reduced.

Answer: Clostridium perfringens

Clostridium perfringens is a common bacteria found in soil and the intestines of humans and animals. It can cause food poisoning when food is improperly cooked or stored at unsafe temperatures, allowing the bacteria to multiply and produce toxins. These toxins cause the characteristic symptoms of food poisoning, such as diarrhea and cramps.

The other options are incorrect:

• Clostridium botulinum: This bacteria produces a potent neurotoxin that causes botulism, a serious illness with symptoms like muscle weakness, difficulty breathing, and paralysis. Botulism is not typically caused by food poisoning.
• Corynebacterium diphtheriae: This bacterium is responsible for diphtheria, a respiratory illness characterized by sore throat, fever, and a thick coating in the back of the throat. Diphtheria is not transmitted through food.
• Clostridium tetani: This bacteria causes tetanus, a severe illness affecting the nervous system and leading to muscle stiffness and painful spasms. Tetanus is not transmitted through food but by contamination of wounds with the bacteria.

Answer: Autoclave

An autoclave is a pressurized chamber that uses high-temperature steam (typically 121°C) to sterilize culture media, equipment, and other laboratory materials. This method effectively kills all microorganisms, including bacteria, viruses, and spores, ensuring a sterile environment for cell culture experiments.

The other options are incorrect:

• Hot Air Oven: While hot air ovens can be used for sterilization of some heat-resistant glassware and metal instruments, they are not suitable for culture media. High temperatures can break down components in the media, rendering it unsuitable for cell growth.
• Pasteurization: Pasteurization uses a milder heat treatment compared to autoclaving and is primarily used for food preservation. It eliminates some, but not all, harmful microbes and is not sufficient for complete sterilization needed for culture media.

Answer: Sterilization

Sterilization refers to a process that eliminates or destroys all forms of life, including bacteria, viruses, fungi, and most importantly, their spores. Spores are dormant stages some microorganisms form that are highly resistant to harsh environmental conditions, including disinfectants. Sterilization ensures a complete absence of viable microorganisms.

The other options are incorrect:

• Disinfection: Disinfection refers to a process that significantly reduces the number of pathogenic microorganisms (those that cause disease) on a surface or in a fluid. However, disinfection may not eliminate all microorganisms, especially spores.
• Incineration: Incineration involves burning waste materials at high temperatures. While this process effectively destroys most microorganisms, it might not achieve complete sterilization, especially in the case of deeply embedded spores or within large materials.
• Lysis: Lysis refers specifically to the rupturing or breaking open of a cell, often caused by enzymes or certain chemicals. While lysis can kill some microorganisms, it is not a guaranteed method of sterilization as it may not be effective against all types or all stages (e.g., spores) of microorganisms.

Answer: Disinfection

Disinfection refers to the process of reducing the number of pathogens (disease-causing microorganisms) on surfaces, objects, or in fluids to a safe level. It does not necessarily eliminate all microorganisms, but aims to significantly decrease the population to a point where the risk of infection is minimal.

The other options are incorrect:

• Sterilization: Sterilization, as explained previously, is a more rigorous process that destroys all forms of life, including pathogens and their spores. It’s used for critical applications like surgical instruments or culture media.
• Incineration: While incineration involves burning waste at high temperatures and can effectively destroy many pathogens, it’s not a controlled process for disinfecting surfaces or liquids. There’s also a risk of incomplete burning leaving behind viable microorganisms.
• Lysis: Lysis, the bursting of cells, can kill some pathogens, but it’s not a reliable disinfection method. Lysis may not be effective against all types of microorganisms or their spores, and the released cellular material could even harbor pathogens.

Answer: Mycobacterium tuberculosis

Mycobacterium tuberculosis is a rod-shaped bacterium with a thick waxy cell wall that makes it resistant to some staining techniques and antibiotics. This bacterium is the primary cause of tuberculosis (TB), a highly contagious infectious disease that typically affects the lungs.

The other options are incorrect:

• Mycobacterium leprae: This bacterium causes leprosy, a chronic infectious disease that mainly affects the peripheral nerves, skin, and mucous membranes.
• Treponema pallidum: This is a spiral-shaped bacterium responsible for syphilis, a sexually transmitted disease with various stages and symptoms.
• Borrelia species: These are a group of spirochete bacteria that cause various tick-borne illnesses, including Lyme disease.

Answer: Treponemapallidum

Treponema pallidum is a spiral-shaped bacterium with a motile structure that allows it to move through tissues. This bacterium is the sole cause of syphilis, a sexually transmitted infection that can progress through various stages if left untreated.

The other options are incorrect:

• Mycobacterium tuberculosis: This bacterium, as mentioned earlier, is responsible for tuberculosis, a respiratory illness.
• Mycobacterium leprae: This bacterium causes leprosy, a chronic infection affecting the skin and nerves.
• Borrelia species: These are a group of bacteria transmitted by ticks and cause tick-borne illnesses like Lyme disease.

Answer: Both Boiling & Autoclaving

• Boiling: Boiling is a simple method of sterilization that involves immersing the object or substance in boiling water for a specific duration. While it may not be as effective as other methods, it can eliminate many vegetative forms of bacteria and some viruses.
• Autoclaving: Autoclaving is a more effective method of sterilization that utilizes high-pressure saturated steam at a temperature of 121°C (250°F) for a specific duration. It effectively kills or inactivates microorganisms, including their spores, and is commonly used for sterilizing laboratory equipment, media, and surgical instruments.

Incorrect Options:

• Hot air oven: A hot air oven is a dry heat method of sterilization, not a moist heat method. It relies on convection currents of hot air to sterilize objects at temperatures typically ranging from 160°C to 180°C. While it is effective for certain materials that are heat-resistant, it may not be suitable for heat-sensitive materials or those that are sensitive to moisture.

Answer: 121°C for 15 min

The standard temperature and time combination used for autoclaving to achieve sterilization is 121°C (250°F) for a minimum of 15 minutes. This combination of moist heat and pressure effectively destroys all microorganisms, including bacteria, viruses, and most importantly, their spores.

The other options are incorrect:

• 100°C for 10 min: Boiling water (100°C) is not sufficient for sterilization, especially for heat-resistant spores. A longer duration wouldn’t overcome this limitation.
• 100°C for 30 min: As explained above, 100°C is not a high enough temperature for sterilization, regardless of the duration.
• 121°C for 30 min: While 121°C is the correct temperature for autoclaving, 15 minutes is the minimum recommended time for sterilization. Longer durations may be used for specific circumstances depending on the load within the autoclave.

Answer: Lactic acid

Lactic acid is the first organic acid produced by most microbial fermentation processes. It is a byproduct of the breakdown of sugars (glucose) by certain bacteria in the absence of oxygen. This process, called lactic acid fermentation, is used in various food products like yogurt, cheese, and sauerkraut.

The other options are incorrect:

• Acetic Acid: While acetic acid is another common organic acid produced by fermentation, it typically requires a specific type of bacteria (Acetobacter) and often occurs in a second stage of fermentation following lactic acid production.
• Butyric Acid: Butyric acid can also be a product of fermentation by some bacteria, but it’s less common than lactic acid and often produced under specific conditions.
• None of the Above: At least some lactic acid production occurs in most fermentation processes, making it the most likely first organic acid to be produced.