MicroBiology MCQs with Answer and Explnation | Chapter 28

Answer: Cellulose

S. aureus does not produce cellulose, a complex carbohydrate primarily synthesized by plants and certain bacteria like Acetobacter and Rhizobia. While cellulose serves diverse functions in these organisms, it offers no known benefit for S. aureus and is not part of its metabolic or pathogenic arsenal.

The other options are incorrect:

• Lipase: S. aureus secretes lipases, enzymes that break down fats and triglycerides, aiding in nutrient acquisition and tissue invasion.
• Coagulase: As discussed earlier, coagulase is a crucial virulence factor for S. aureus, helping it clot blood and evade immune defenses.
• Lecithinase: S. aureus also produces lecithinases, enzymes that degrade lecithin, a phospholipid component of cell membranes, facilitating tissue damage and bacterial spread.

Answer: Group C carbohydrate antigen

Lancefield grouping classifies streptococci based on polysaccharide antigens present in their cell wall. Group C specifically refers to the presence of a unique polysaccharide antigen in the cell wall of Group C streptococci. M protein, peptidoglycan, and M antigen are not specific to Group C and can be present in other streptococcal groups or even other bacteria.

The other options are incorrect:

• M protein: While M protein is a major virulence factor in certain streptococcal groups, particularly Group A, it is not specifically used for Lancefield grouping and can be present in other groups as well.
• Group C peptidoglycan cell wall: Peptidoglycan is a major component of the cell wall in all bacteria, including streptococci. It is not specific to any particular group and cannot be used for Lancefield grouping.
• M antigen: M antigen is another virulence factor found in some streptococcal groups, including Group A and Group C. Like M protein, it is not specific to Group C and cannot be used for Lancefield grouping.

Answer: Streptococcus mutans

Among the listed options, Streptococcus mutans is the primary culprit for dental caries. This bacterium ferments sugars in the mouth, producing lactic acid that demineralizes tooth enamel and leads to cavities.

The other options are incorrect:

• Streptococcus pyogenes: This species, also known as Group A Streptococcus, is more commonly associated with throat infections, skin infections, and scarlet fever. While it can be present in the mouth, it plays a minimal role in dental caries.
• Streptococcus pneumoniae: This bacterium, responsible for pneumonia and meningitis, typically resides in the respiratory tract and rarely contributes to dental caries.
• Streptococcus bovis: This species lives in the gastrointestinal tract and occasionally causes endocarditis but isn’t involved in dental caries development.

Answer: Pneumococcus

The quelling phenomenon is observed in Pneumococcus, specifically in the context of the identification of encapsulated strains of Streptococcus pneumoniae. This phenomenon refers to the ability to detect the presence of the polysaccharide capsule surrounding the bacterial cells using specific antibodies, leading to the swelling or quelling of the capsule.

The other options are incorrect:

• Streptococcus:While Streptococcus pneumoniae, a type of streptococcus, exhibits the quelling phenomenon, not all streptococci display this characteristic.
• Staphylococcus:The quelling phenomenon is not typically associated with Staphylococcus. Staphylococci are known for causing a range of infections but do not exhibit quelling.
• Hemophilus: Hemophilus is not known for the quelling phenomenon. It is a genus of bacteria that includes species like Haemophilus influenzae, which is known for causing respiratory tract infections.

Answer: Optochin sensitivity

To identify the group of streptococci causing the development of pustules in this case, the Optochin sensitivity test is used. Streptococcus pneumoniae, which is known to cause pustules and respiratory infections, is sensitive to Optochin, while other streptococci are not.

The other options are incorrect:

• Bacitracin sensitivity: The Bacitracin sensitivity test is used to differentiate between group A streptococci (sensitive) and other beta-hemolytic streptococci (resistant).
• Novobiocin sensitivity: Novobiocin sensitivity is typically used to distinguish between coagulase-negative staphylococci, where Staphylococcus saprophyticus is novobiocin sensitive, and other species which are not.
• Hemolysis test: Hemolysis test is a general test to categorize streptococci based on their ability to lyse red blood cells. While it can give information about hemolysis, it doesn’t specifically identify the organism causing the infection. The Optochin sensitivity test is more specific in this context.

Answer: Beta hemolysin

The “hot-cold phenomenon” is associated with the beta hemolysin toxin produced by Staphylococcus aureus. This phenomenon refers to the enhanced hemolysis observed when blood agar plates are incubated at elevated temperatures (37 degrees Celsius or higher) and then exposed to lower temperatures.

The other options are incorrect:

• Alpha hemolysin: Alpha hemolysin is produced by some strains of Staphylococcus aureus, but it is not specifically associated with the hot-cold phenomenon. It causes complete hemolysis and does not exhibit the temperature-dependent enhancement seen in the hot-cold phenomenon.
• Gamma hemolysin: Gamma hemolysin is not a known toxin produced by Staphylococcus aureus. The hot-cold phenomenon is not related to gamma hemolysin.
• Theta hemolysin: Theta hemolysin is not a recognized toxin produced by Staphylococcus aureus. The hot-cold phenomenon is specifically associated with beta hemolysin.

Answer: Catalase test

Staphylococcus differs from Streptococcus primarily by the catalase test result. Staphylococci are catalase positive, meaning they produce the enzyme catalase, which can break down hydrogen peroxide into water and oxygen. Streptococci, on the other hand, are catalase negative, lacking this enzyme.

The other options are incorrect:

• Coagulase test: The coagulase test is used to differentiate between coagulase-positive Staphylococcus aureus and coagulase-negative staphylococci. It is not a distinguishing factor between Staphylococcus and Streptococcus.
• Phosphatase test: The phosphatase test is not commonly used to differentiate between Staphylococcus and Streptococcus. It is more relevant for other bacterial identification purposes.
• Gram-negative: Staphylococcus and Streptococcus are both Gram-positive bacteria. Gram-negative bacteria have a different cell wall structure, and this characteristic is not a point of differentiation between Staphylococcus and Streptococcus.

Answer: They commonly infect indwelling prosthesis

While non-coagulase Staphylococci (CoNS) are generally less virulent than coagulase-positive staphylococci like S. aureus, they can cause infections, especially in healthcare settings. Indwelling prostheses like catheters and implants provide surfaces for bacterial adherence and biofilm formation, increasing the risk of CoNS-associated infections.

The other options are incorrect:

• They are non-pathogenic: Although less common than S. aureus infections, CoNS can cause various infections, including skin and soft tissue infections, bloodstream infections, and urinary tract infections.
• They may cause scarlet fever: Scarlet fever is primarily caused by Group A Streptococcus pyogenes, not CoNS.
• They are separated by Gram’s staining: Both CoNS and coagulase-positive Staphylococci are Gram-positive cocci, so Gram staining cannot differentiate them.

Answer: S. aureus

Catalase positive, β-hemolytic Staphylococci typically refers to Staphylococcus aureus. This bacterium is catalase positive, meaning it produces the enzyme catalase, and it exhibits beta-hemolysis on blood agar plates, causing complete lysis of red blood cells.

The other options are incorrect:

• S. epidermidis: Staphylococcus epidermidis is catalase positive but is usually not β-hemolytic. It is associated with opportunistic infections, especially those related to medical devices.
• S. saprophyticus: Staphylococcus saprophyticus is catalase positive but is typically not β-hemolytic. It is often associated with urinary tract infections.
• Pneumococci: Pneumococci, referring to Streptococcus pneumoniae, is not a Staphylococcus species. It is a catalase-negative, α-hemolytic bacterium belonging to the Streptococcus genus.

Answer: Streptococcus agalactiae

A positive CAMP test is indicative of the presence of Group B Streptococcus (Streptococcus agalactiae). The CAMP test is a diagnostic test used to identify the enhanced hemolysis produced when Streptococcus agalactiae is grown adjacent to Staphylococcus aureus on a blood agar plate.

• The other options are incorrect:

• Staphylococcus aureus: Staphylococcus aureus is not associated with a positive CAMP test. This test is specific for identifying Streptococcus agalactiae.
• E. coli: Escherichia coli is a common cause of neonatal meningitis, but it is not detected by the CAMP test. The CAMP test is designed for Streptococcus agalactiae.
• Hemophilus influenzae: Hemophilus influenzae is another potential cause of neonatal meningitis, but it is not identified by the CAMP test. The CAMP test is specific for Streptococcus agalactiae.

Answer: Streptococcus

The most common organism responsible for postsplenectomy infections is Streptococcus pneumoniae. The spleen plays a crucial role in the immune system, particularly in clearing encapsulated bacteria like S. pneumoniae. Asplenic (lacking a spleen) individuals are at an increased risk of severe infections, especially from encapsulated bacteria.

The other options are incorrect:

• Staphylococcus: While Staphylococcus can cause infections, it is not the most common organism associated with postsplenectomy infections. Streptococcus pneumoniae is the primary concern in these cases.
• Pseudomonas: Pseudomonas is not a common organism responsible for postsplenectomy infections. Encapsulated bacteria like Streptococcus pneumoniae pose a greater risk.
• Influenza Virus: Influenza virus can predispose individuals to secondary bacterial infections, but it is not a direct cause of postsplenectomy infections. Streptococcus pneumoniae is a more significant concern in this context.

Answer: Streptococcus agalactiae

The combination of β-hemolysis, bacitracin resistance, and a positive CAMP test is characteristic of Streptococcus agalactiae (Group B Streptococcus or GBS). The CAMP test is specifically used to identify the enhanced hemolysis when Streptococcus agalactiae is grown adjacent to Staphylococcus aureus on a blood agar plate.

The other options are incorrect:

• Streptococcus pyogenes: Streptococcus pyogenes (Group A Streptococcus) is sensitive to bacitracin and is not CAMP positive. It causes β-hemolysis but lacks the specific characteristics mentioned.
• Streptococcus pneumoniae: Streptococcus pneumoniae is sensitive to bacitracin and does not exhibit a positive CAMP test. It also causes α-hemolysis, not β-hemolysis.
• Enterococcus faecalis: Enterococcus faecalis is resistant to bacitracin but is not known for β-hemolysis and is not CAMP positive. It belongs to the Enterococcus genus, not the Streptococcus genus.

Answer: Enterococcus faecalis

The characteristics described, including β-hemolysis, resistance to vancomycin, growth in 6.5% NaCl, and nonbile sensitivity, are indicative of Enterococcus faecalis. Enterococci are known for their ability to grow in high salt concentrations and resistance to vancomycin, making them distinct from other streptococci.

The other options are incorrect:

• Streptococcus agalactiae: Streptococcus agalactiae is generally sensitive to vancomycin, and it does not typically show growth in 6.5% NaCl. It is also bile-sensitive.
• Streptococcus pneumoniae: Streptococcus pneumoniae is sensitive to vancomycin and is bile-sensitive. It is not known for growth in high salt concentrations.
• Streptococcus bovis: Streptococcus bovis may grow in 6.5% NaCl, but it is usually sensitive to vancomycin. The other characteristics described do not align with S. bovis.

Answer: Streptococcus pneumoniae

The presence of α-hemolytic colonies on blood agar suggests Streptococcus pneumoniae. This bacterium is known for causing infections such as pneumonia, and its characteristic α-hemolysis is observed as a greenish discoloration around colonies on blood agar.

The other options are incorrect:

• Staphylococcus aureus: Staphylococcus aureus typically produces β-hemolysis on blood agar. The α-hemolysis described in the question is not characteristic of S. aureus.
• Legionella: Legionella is not typically cultured from routine blood agar plates, and its colonies do not exhibit α-hemolysis. Legionella is associated with Legionnaires’ disease.
• Streptococcus pyogenes: Streptococcus pyogenes (Group A Streptococcus) usually produces β-hemolysis on blood agar. The α-hemolysis described is not consistent with S. pyogenes.

Answer: Streptococcus

The most common organism causing sore throat is Streptococcus, specifically Streptococcus pyogenes. This bacterium is responsible for a significant number of cases of pharyngitis, commonly known as strep throat.

The other options are incorrect:

• Staphylococcus: While Staphylococcus aureus can cause various infections, including skin and soft tissue infections, it is not the primary organism associated with sore throat.
• Hemophilus: Haemophilus influenzae can cause respiratory infections, but it is not the most common organism causing sore throat. Streptococcus pyogenes is more frequently associated with this condition.
• Bacillus: Bacillus species are not typically associated with causing sore throat. Streptococcus pyogenes remains the predominant organism responsible for this condition.

Answer: Capsular swelling

The Quellung reaction refers to the swelling of bacterial capsules when exposed to specific antisera. It is a method used to identify the presence of capsules around bacteria. The correct option is B, “Capsular swelling,” as the reaction involves the swelling of the bacterial capsule when interacting with specific antibodies.

The other options are incorrect:

• A. Mitochondrial swelling: The Quellung reaction is not related to mitochondrial swelling. It specifically involves the bacterial capsule.
• C. RBC swelling: The Quellung reaction is not associated with red blood cell (RBC) swelling. It is focused on the identification of bacterial capsules.
• D. Cell wall swelling: The Quellung reaction does not involve the swelling of the bacterial cell wall. It is a phenomenon related to the bacterial capsule.

Answer: Pneumococcus

Frederick Griffith conducted his famous experiment on bacterial transformation using Streptococcus pneumoniae, also known as pneumococcus. He demonstrated that genetic material could be transferred from a heat-killed strain of virulent pneumococcus (type III-S) to a live non-virulent strain (type II-R), transforming the latter into a virulent form. This experiment laid the foundation for our understanding of DNA as the carrier of genetic information.

The other options are incorrect:

• Enterococcus: While also Gram-positive bacteria, enterococcus was not used in Griffith’s experiment on transformation.
• Gonococcus: This Gram-negative bacteria, responsible for gonorrhea, was not the subject of Griffith’s pioneering work on transformation.
• Staphylococcus: While another important genus of Gram-positive bacteria, staphylococcus was not used in Griffith’s classic experiment on transformation.

Answer: Single dose of tetanus toxoid

In the case of a clean wound and a person who has received complete immunization against tetanus within the last 10 years, the recommended action is to administer a single booster dose of tetanus toxoid. The protection provided by previous immunization should be sufficient, and a full course is not required for clean wounds.

The other options are incorrect:

• Full course of tetanus toxoid: A full course of tetanus toxoid is not necessary in this scenario. A single booster dose is sufficient.
• Human tetanus globulin: Human tetanus globulin is used for passive immunization in individuals who have not been previously immunized or whose immunization status is uncertain. In this case, with a clean wound and recent immunization, it is not the first-line recommendation.
• Human tetanus globulin and single dose of toxoid: In this scenario, where the wound is clean and the person has a history of complete immunization within the last 10 years, administration of both human tetanus globulin and a single dose of toxoid is unnecessary. A single dose of toxoid alone is recommended.

Answer: Neisseria meningitidis

While all the listed bacteria can be causative agents of neonatal meningitis, Neisseria meningitidis is not as commonly associated with acute neonatal meningitis (occurring in the first week of life) .

The other options are incorrect:

• Escherichia coli (E. coli): One of the most frequent causes of early-onset neonatal meningitis, particularly in cases related to maternal ascending infections or healthcare-associated transmission.
• Streptococcus agalactiae (Group B Streptococcus, GBS): The leading cause of early-onset neonatal meningitis, often transmitted vertically from mother to infant during birth.
• Listeria monocytogenes: Primarily responsible for late-onset neonatal meningitis (occurring after the first week of life), typically acquired through transplacental transmission or postnatal exposure.

Answer: All of the above

Neisseria infections, particularly those caused by Neisseria meningitidis and Neisseria gonorrhoeae, can be exacerbated by deficiencies in various components of the complement system, especially the late complement pathway. This system plays a crucial role in opsonization and destruction of invading bacteria. Deficiencies in specific components can significantly impair the immune response against Neisseria, increasing susceptibility to infections.

Answer: Maltose fermentation

Maltose fermentation: While both bacteria are Gram-negative cocci, their ability to ferment maltose differs. N. gonorrhoeae ferments maltose, producing acid and gas, while N. meningitidis does not ferment maltose. This distinctive biochemical characteristic provides a reliable method for differentiating these closely related species.

The other options are incorrect:

• Glucose fermentation: Both N. gonorrhoeae and N. meningitidis ferment glucose, making it unsuitable for differentiation.
• VP reaction: Both often give a positive VP reaction, not reliable for discrimination.
• Indole test: Both are indole-negative, again not helpful for differentiation.

Answer: Staphylococcus epidermidis

Staphylococcus epidermidis is catalase positive but coagulase negative. This bacterium is a part of the normal skin flora and is often associated with infections related to medical devices. The catalase test helps differentiate staphylococci from streptococci, and the coagulase test is useful in distinguishing between pathogenic Staphylococcus aureus (coagulase positive) and less pathogenic Staphylococcus epidermidis (coagulase negative).

The other options are incorrect:

• Streptococcus pyogenes: Streptococcus pyogenes is catalase negative. It belongs to the Streptococcus genus, not Staphylococcus.
• Staphylococcus aureus: Staphylococcus aureus is catalase positive and coagulase positive. It is known for causing a variety of infections, including skin and soft tissue infections.
• Enterococci: Enterococci are catalase negative. They are a group of bacteria that include Enterococcus faecalis and Enterococcus faecium, and they are known for their ability to cause infections in the gastrointestinal and urinary tracts.

Answer: Neisseria

Gram-negative cocci are often associated with the Neisseria genus. Neisseria gonorrhoeae and Neisseria meningitidis are two significant pathogenic species within this genus. The chocolate agar medium is conducive to the growth of fastidious organisms like Neisseria.

The other options are incorrect:

• Hemophilus: Hemophilus species are more commonly Gram-negative rods. They are often associated with respiratory infections.
• Streptococcus: Streptococcus species are generally Gram-positive cocci. They are not typically associated with being Gram-negative.
• Staphylococcus: Staphylococcus species are Gram-positive cocci. They do not match the description of Gram-negative cocci observed on the chocolate agar.

Answer: Gram-negative diplococci, in pus cells

CSF (Cerebrospinal Fluid) in meningococcal meningitis typically shows Gram-negative diplococci. The causative agent, Neisseria meningitidis, is a Gram-negative diplococcus. Examination of the CSF may reveal the presence of these bacteria, often within pus cells.

The other options are incorrect:

• Gram-positive diplococci, in pus cells:This description is not characteristic of meningococcal meningitis. Gram-positive diplococci are more indicative of organisms like Streptococcus pneumoniae.
• Gram-negative bacilli, in pus cells: Gram-negative bacilli are not the typical morphology seen in meningococcal meningitis. Neisseria meningitidis presents as Gram-negative diplococci.
• Gram-positive bacilli, in pus cells: Gram-positive bacilli are not typical in meningococcal meningitis. This description is more consistent with organisms like Bacillus species.

Answer: Gas is invariable present in muscle compartments

The presence of gas in muscle compartments is a distinctive sign of gas gangrene, which is caused by Clostridium perfringens and other anaerobic Gram-positive bacteria. These bacteria produce gas as they multiply within the damaged muscle tissue. The other options are incorrect for the following reasons:

The other options are incorrect:

• It is due to Clostridium botulinum infection: As mentioned, botulism is caused by a different Clostridium species and has different symptoms.
• Clostridia are Gram-negative anaerobes: This is factually incorrect. Clostridia are Gram-positive bacteria.
• Clinical features are due to protein endotoxin: Clostridia produce exotoxins, not endotoxins. Endotoxins are associated with Gram-negative bacteria.

Answer: All of the above

All three listed Clostridium species (C. novyi, C. septicum, and C. perfringens) can cause gas gangrene. In fact, they are among the most common culprits for this life-threatening infection. While C. perfringens is responsible for the majority of cases, the other two can also contribute significantly, particularly in mixed infections.

Answer: Clostridium perfringens

While Clostridium species are known for various toxins and illnesses, only Clostridium perfringens is associated with necrotizing gastrointestinal enteritis (NE). This inflammatory condition primarily affects premature infants and is characterized by tissue death and inflammation in the intestine. C. perfringens produces toxins that damage the intestinal wall, leading to the typical symptoms of NE.

The other options are incorrect:

• Clostridium difficile: This bacteria causes pseudomembranous colitis, a different type of intestinal inflammation often associated with antibiotic use. While it can affect infants, it doesn’t cause NE.
• Clostridium tetani: This species is responsible for tetanus, a neurological disease affecting muscle contraction. It has no involvement in NE.
• Clostridium botulinum: This bacteria produces the botulinum toxin, causing botulism, characterized by muscle paralysis. It doesn’t contribute to NE.

Answer: Clostridium perfringens

While several Clostridium species cause different illnesses, only C. perfringens is linked to necrotizing gastrointestinal enteritis (NE). This condition mainly affects premature infants and involves tissue death and inflammation in the intestine. C. perfringens produces toxins that damage the intestinal wall, leading to the typical symptoms of NE.

The other options are incorrect:

• Clostridium difficile: This bacteria causes pseudomembranous colitis, a different type of intestinal inflammation often associated with antibiotic use. While it can affect infants, it doesn’t cause NE.
• Clostridium tetani: This species is responsible for tetanus, a neurological disease affecting muscle contraction. It has no involvement in NE.
• Clostridium botulinum: This bacteria produces the botulinum toxin, causing botulism, characterized by muscle paralysis. It doesn’t contribute to NE.

Answer: Injection of human antiserum

While a 10-year-old boy with a contaminated wound from a road accident needs careful management, injecting human antiserum is unnecessary given his immunization history and the timing of the injury. Here’s a breakdown of all options and why they can or cannot be done.

The other options are incorrect:

• Injection of tetanus toxoid: This option is appropriate. Although he received boosters years ago, a contaminated wound necessitates a booster dose to ensure sufficient tetanus protection.
• Broad spectrum antibiotics: This is essential for preventing potential infections arising from the contaminated wound.
• Wound debridement and cleaning: This crucial step removes dirt, debris, and damaged tissue, minimizing the risk of infection and promoting healing

Answer: Bacteriophage

Bacteriophages are the only type of virus on this list that contain the enzyme lysozyme. Lysozyme helps them break down the cell walls of their host bacteria, which are made of peptidoglycan. This allows the bacteriophage to inject its genetic material into the bacterium and hijack its cellular machinery for replication.

The other options are incorrect:

• Animal viruses: Animal viruses, including those that cause common colds and flu, do not contain lysozyme. They typically gain entry into host cells by fusing with the cell membrane or by being endocytosed (engulfed) by the cell.
• Plant viruses: Plant viruses also lack lysozyme. They typically enter plant cells through damaged cell walls or through natural openings in the plant’s tissues.
• Human viruses: Human viruses, like HIV and the common cold virus, do not contain lysozyme. They use various mechanisms to gain entry into host cells, such as by binding to specific receptors on the cell surface.

Answer: Predominantly seen in dry and winter season

While C. tetani spores can indeed be found in soil and the intestines of humans and animals, their incidence remains relatively constant throughout the year and is not significantly influenced by specific seasons.

The other options are incorrect:

• Soil & intestine of human / animals are reservoirs: This is accurate. C. tetani spores persist in these environments, waiting for an opportunity to enter a wound and germinate.
• Transmission through contaminated wounds: This is also correct. When spores enter a wound and find anaerobic conditions, they germinate and produce the tetanospasmin toxin, causing the characteristic muscle spasms associated with tetanus.
• No heard immunity is seen: This is true. Unlike some other infectious diseases, tetanus does not confer significant herd immunity. Immunity relies solely on vaccination or previous infection.

Answer: Herpesviruses

Herpesviruses are notorious for their ability to establish latent infections, particularly in neurons. This means they can infect a host cell, integrate their genetic material into the host’s DNA, and then remain dormant for extended periods. When triggered by certain factors like stress, illness, or immunosuppression, the virus can reactivate and cause disease symptoms

The other options are incorrect:

• Togaviruses: Togaviruses typically do not establish long-term latent infections. They are known for causing diseases such as rubella and alphaviruses like chikungunya virus.
• Enteroviruses: Enteroviruses, including polioviruses and coxsackieviruses, generally do not establish latent infections in neurons. They often cause acute infections.
• Rhinoviruses: Rhinoviruses, causing the common cold, do not establish latent infections. They primarily cause short-term respiratory infections.

Answer: Tetanus toxoid

The most effective way to prevent tetanus is through vaccination with tetanus toxoid. Tetanus toxoid is a vaccine that induces immunity against the toxin produced by Clostridium tetani, the bacterium that causes tetanus. Routine immunization, including primary series and booster doses, is crucial to maintain protection

The other options are incorrect:

• Surgical debridement and toilet: This is crucial for managing contaminated wounds and reducing the risk of infection, but it doesn’t prevent tetanus specifically. If someone hasn’t been vaccinated, they are still susceptible after wound cleaning.
• Hyperbaric oxygen: This therapy can be helpful in severe cases of tetanus by inhibiting toxin action in tissues. However, it’s not a preventive measure and requires prior tetanus vaccination for maximum efficacy.
• Antibiotics: Antibiotics are essential for treating bacterial infections that might accompany a contaminated wound, but they don’t directly prevent tetanus. They won’t neutralize the tetanus toxin if someone is infected.

Answer: Botulism

The symptoms of acute onset descending paralysis, including blurred vision and non-reactive pupils, are indicative of botulism. Botulism is caused by the neurotoxin produced by Clostridium botulinum bacteria. The toxin inhibits the release of acetylcholine at neuromuscular junctions, leading to paralysis. The descending pattern of paralysis, along with cranial nerve involvement, is characteristic of botulism.

The other options are incorrect:

• Poliomyelitis: While also causing paralysis, polio typically affects younger children and has a different pattern of involvement, often starting in the lower limbs.
• Diphtheria: The characteristic symptom of diphtheria is a sore throat with a thick, grayish membrane. Additionally, descending paralysis is less common.
• Porphyria: This group of metabolic disorders can cause neurological symptoms but wouldn’t typically present with acute paralysis and fixed pupils.

Answer: Clostridium difficile

The patient’s symptoms, specifically the development of diarrhea after antibiotic therapy (amoxicillin) in the setting of acute lymphocytic leukemia and neutropenia, are suggestive of antibiotic-associated diarrhea, particularly caused by Clostridium difficile infection. Antibiotic use can disrupt the normal balance of gut microbiota, leading to overgrowth of C. difficile and the production of toxins, which can cause diarrhea.

The other options are incorrect:

• Salmonella typhi: Salmonella typhi is more commonly associated with typhoid fever and is not a typical cause of antibiotic-associated diarrhea.
• Clostridium perfringens: While Clostridium perfringens can cause food poisoning and gastroenteritis, it is not a common cause of antibiotic-associated diarrhea.
• Shigella flexneri: Shigella flexneri is a bacterium associated with bacillary dysentery, not typically implicated in antibiotic-associated diarrhea.

Answer: Proteus mirabilis

Swarming growth on culture is characteristic of Proteus mirabilis, a Gram-negative bacterium. Swarming is a unique phenomenon where bacteria spread rapidly across the surface of solid agar in a coordinated and multicellular manner. Proteus mirabilis is known for its swarming motility, and this pattern of growth is one of its distinguishing features in laboratory cultures.

The other options are incorrect:

• Clostridium tetani: Clostridium tetani is not known for swarming growth. It is the bacterium responsible for tetanus.
• Clostridium botulinum: Clostridium botulinum does not exhibit swarming growth. It produces the neurotoxin responsible for botulism.
• Bacillus cereus: Bacillus cereus can exhibit swarming growth, but it is a Gram-positive bacterium. Proteus mirabilis is more specifically associated with swarming growth among the options provided.

Answer: Capsid

The capsid is a protein shell that encloses the viral genetic material (DNA or RNA) in all viruses. It protects the genome from damage and facilitates attachment to host cells during infection. Therefore, it’s the only component found in all viruses.

The other options are incorrect:

• The envelope: While some viruses have an outer envelope made of lipids and proteins derived from the host cell, it’s not a universal feature. Many viruses lack an envelope, making it an incorrect option.
• DNA: While DNA is the genetic material in some viruses, RNA is present in others. Since the question asks for a component found in all viruses, DNA is not the correct answer.
• Spikes: Spikes are protein projections on the surface of some viruses, but they are not present in all. Their function is to aid in attachment and entry into host cells, but their absence doesn’t prevent a virus from being classified as a virus.

Answer: Protein

All viruses, regardless of their type or structure, contain proteins. These proteins make up the capsid, a protective shell that encloses the viral genetic material (DNA or RNA). In some viruses, proteins also form spikes on the surface for attachment to host cells. Thus, protein is a universal component of all viruses.

The other options are incorrect:

• Lipid: While some viruses, like those with an envelope, have small amounts of lipids derived from the host cell, it’s not a necessary component. Many viruses lack an envelope and rely solely on proteins.
• DNA: DNA is the genetic material for some viruses, but others use RNA. Since the question asks for a component found in all viruses, DNA alone is not a universal feature.
• RNA: Similar to DNA, RNA is the genetic material for some viruses but not all. Therefore, it’s not a guaranteed component present in every virus.

Answer: Icosahedron

The icosahedron is a highly symmetrical polyhedral shape with 20 triangular faces, 12 vertices, and 30 edges. This structure allows for efficient packing of viral subunits while minimizing gaps and energy expenditure. Thus, it’s a highly favorable shape for many viruses.

The other options are incorrect:

• Pentagon: While polygons like pentagons are building blocks of icosahedral capsids, they are not the complete capsid shape itself.
• Cube: Cubes have 6 square faces and are not as flexible or efficient in forming larger structures compared to icosahedrons for viruses.
• Pyramid: Pyramids have fewer faces and vertices than icosahedrons, limiting their potential for complex and tightly packed capsid formation.

Answer: Variola virus

Smallpox is an infectious disease caused solely by the variola virus. This double-stranded DNA virus belongs to the Orthopoxvirus genus and is distinct from other related viruses.

The other options are incorrect:

• Varicella zoster: This virus causes chickenpox and shingles, two other contagious diseases with some similar symptoms to smallpox. However, it’s a different virus altogether and doesn’t cause smallpox.
• Vaccinia virus: This closely related virus was used in the world’s first successful vaccine against smallpox. While closely related, vaccinia virus itself doesn’t cause smallpox.
• Cowpox virus: This virus, another member of the Orthopoxvirus genus, can cause a mild disease in cows and occasionally humans. However, cowpox is distinct from smallpox and cannot cause the severe symptoms associated with it.

Answer: Hemagglutination

Hemagglutination is a technique used in immunology and virology to detect the presence of antibodies or viruses by their ability to clump red blood cells (agglutination). It’s not a type of cell culture itself.

The other options are incorrect:

• Semi-continuous: These cell lines can divide for a limited number of passages (around 20-50) before losing their replicative potential. Although not immortal, they still represent a type of cell culture.
• Primary: These cultures are derived directly from tissues and typically have a limited lifespan with specific characteristics of the original tissue. Despite their limitations, they remain a vital type of cell culture.
• Continuous: These cell lines have undergone mutations or adaptations that allow them to divide indefinitely. They are a common type of cell culture used in research due to their stability and ease of maintenance.

Answer: Ability to survive in acidic conditions

Enteroviruses differ from rhinoviruses mainly by their ability to survive in acidic conditions. Enteroviruses, including those in the Enterovirus genus (e.g., poliovirus, coxsackievirus), are known for their resilience to the acidic environment of the stomach, allowing them to pass through the gastrointestinal tract and cause systemic infections. In contrast, rhinoviruses are more sensitive to stomach acid and primarily infect the respiratory tract.

The other options are incorrect:

• Type of nucleic acid: Both enteroviruses and rhinoviruses belong to the Picornaviridae family and have single-stranded RNA genomes. The type of nucleic acid is not a distinguishing factor between the two.
• Size: Enteroviruses and rhinoviruses have similar sizes. The size difference is not a significant factor in distinguishing between them.
• Capsid shape: Both enteroviruses and rhinoviruses have icosahedral capsids. Capsid shape is not a distinguishing feature between the two.

Answer: C-carbohydrate antigen is the same

The similarity between the pathogens causing the skin ulcer on the leg and sore throat is that the C-carbohydrate antigen is the same. This indicates that the strains causing both the skin ulcer and sore throat share a common C-carbohydrate antigen.

The other options are incorrect:

• Protein-A is same for both: Protein-A is not typically associated with hemolysis. It is a component found in Staphylococcus aureus but is not relevant to the β-hemolysis seen in the cultures.
• C-carbohydrate antigen is different: The correct answer indicates that the C-carbohydrate antigen is the same for both pathogens causing the skin ulcer and sore throat.
• Strain causing both are the same: The information provided does not suggest that the strains causing both the skin ulcer and sore throat are the same. The similarity is specified to the C-carbohydrate antigen, not necessarily the entire strain.

Answer: Continuous cell line

A continuous cell line is a type of cell culture that can reproduce for an extended number of generations. These cells are often immortalized and can be maintained in culture for a long duration. Continuous cell lines are particularly useful for supporting viral replication and are commonly employed in virology research.

The other options are incorrect:

• Primary cell culture: Primary cell cultures are derived directly from tissues and have a limited lifespan. They are not immortalized and eventually senesce.
• Secondary cell culture: The term “secondary cell culture” is not commonly used. It may refer to the passaging of cells from a primary culture to a subsequent culture but is not a well-defined category of cell culture.
• Diploid fibroblast cell: Diploid fibroblast cells are normal cells with a finite lifespan. They are often used in primary cell cultures but are not continuously replicating. Continuous cell lines are typically immortalized.

Answer: Plaque assays

Bacteriophages are readily counted by the process of plaque assays. Plaque assays involve infecting a monolayer of bacterial cells with a dilution of bacteriophages. Each viable phage forms a plaque, which is a clear zone where bacterial cells have been lysed. Counting the number of plaques allows for the quantification of bacteriophage concentration.

The other options are incorrect:

• Immunoassays: Immunoassays are methods that use antibodies to detect the presence of specific substances. They are not commonly used for counting bacteriophages.
• ELISA (Enzyme-Linked Immunosorbent Assay): ELISA is a type of immunoassay and is not typically used for counting bacteriophages. It is more commonly employed in the detection of specific proteins or antibodies.
• Tissue culture: Tissue culture is a technique used for culturing cells, not for counting bacteriophages. Plaque assays are the standard method for bacteriophage quantification.

Answer: Clostridium perfringens

Most members of the Clostridium genus are motile, possessing peritrichous flagella. However, Clostridium perfringens is a notable exception and lacks flagella. This makes it the only non-motile species listed in the options.

The other options are incorrect:

• Clostridium novyi: This species is motile and known for its production of alpha toxin, causing gas gangrene.
• Clostridium botulinum: Motile as well, C. botulinum produces the infamous botulinum toxin responsible for botulism.
• Clostridium difficile: Another motile species, C. difficile is infamous for causing pseudomembranous colitis.

Answer: Adenovirus

Adenovirus is not an RNA virus; it is a DNA virus. Adenoviruses have a double-stranded DNA genome, not an RNA genome. They can cause a range of respiratory, gastrointestinal, and ocular infections in humans.

The other options are incorrect:

• Retrovirus: Retroviruses have a single-stranded RNA genome and use reverse transcriptase to convert their RNA into DNA, which is then integrated into the host cell genome.
• Enterovirus: Enteroviruses, such as poliovirus and coxsackievirus, have a single-stranded RNA genome.
• Rhabdovirus: Rhabdoviruses, including the rabies virus, have a single-stranded RNA genome.

Answer: Respiratory enteric orphans

In the name of the family Reoviridae, the term ‘reo’ refers to “respiratory enteric orphans.” This family includes double-stranded RNA viruses that were initially discovered in association with respiratory and enteric infections. The “orphans” part of the name indicates that these viruses do not belong to other established virus families.

The other options are incorrect:

• Respiratory: While Reoviridae viruses are associated with respiratory infections, the term ‘reo’ specifically refers to respiratory enteric orphans.
• Enteric: Reoviridae viruses are indeed associated with enteric infections, but the term ‘reo’ encompasses both respiratory and enteric aspects.
• Orphans: While the term ‘orphans’ is part of the name, it doesn’t convey the meaning of ‘reo.’ The term ‘reo’ is the key component that refers to respiratory enteric orphans.

Answer: Herpesvirus

Herpesviruses are notorious for their ability to establish latent infections. This means they can invade host cells, integrate their viral DNA into the host genome, and remain dormant for extended periods. During latency, the virus doesn’t actively produce new virus particles and may cause no symptoms. However, it can reactivate under certain conditions, such as stress, immunosuppression, or injury, leading to recurrent infections.

The other options are incorrect:

• Adenovirus: While some adenoviruses can persist in lymphoid tissues after initial infection, they typically don’t exhibit true latency with integration into the host genome.
• Hepatitis B Virus: HBV can establish chronic infections, meaning persistent production of viral particles and ongoing liver damage. However, this isn’t the same as latency, where the virus remains inactive within the host genome.
• Influenza virus: Influenza viruses replicate actively in the respiratory tract and don’t establish latent infections. Once the infection resolves, the virus is cleared from the body.

Answer: Virus infections are all life threatening

While many viral infections can be serious and even fatal, not all of them carry such consequences. Many viral infections are mild and resolve on their own, such as the common cold or a typical case of influenza. Therefore, it’s not accurate to say that all viral infections are life-threatening.

The other options are incorrect:

• Number of viruses cause similar symptoms: This is true. Many viruses, especially within the same family, can share similar symptoms due to their targeting of similar tissues and cellular mechanisms. For example, both rhinoviruses and coronaviruses can cause respiratory infections with symptoms like cough, fever, and sore throat.
• Virus infection may cause immunosuppression: This is also true. Some viruses, like HIV, directly target and weaken the immune system, making individuals more susceptible to other infections and diseases.
• Some viruses require other viruses for replication: This is true for a specific group of viruses called satellite viruses. They lack essential genes for their own replication and rely on helper viruses to provide the necessary components and machinery.