MicroBiology MCQs with Answer and Explnation | Chapter 31

Answer: Is coagulase positive

Staphylococcus aureus (Staph. aureus) differs from Staphylococcus epidermidis (S. epidermidis) by being coagulase positive. Coagulase is an enzyme produced by Staph. aureus that can cause the plasma to clot, a characteristic not shared by S. epidermidis.

The other options are incorrect:

• Forms white colonies: Colony color is not a differentiating factor between Staph. aureus and S. epidermidis. Staph. aureus can form colonies of various colors.
• A common cause of UTI: Staph. aureus is not a common cause of urinary tract infections (UTIs). Other bacteria, such as Escherichia coli, are more frequently associated with UTIs.
• Causes endocarditis of prosthetic valve: While Staph. aureus can cause endocarditis, it is not specifically associated with prosthetic valves. Staphylococcus epidermidis is more commonly implicated in prosthetic valve endocarditis due to its ability to form biofilms on medical

Answer: Staphylococcus aureus

The scenario described, with rapid onset (4-6 hours) of severe gastroenteritis after consuming snacks, is characteristic of food poisoning caused by Staphylococcus aureus. Staphylococcus aureus produces heat-stable enterotoxins that can lead to acute gastrointestinal symptoms shortly after ingestion.

The other options are incorrect:

• Salmonella typhi: Salmonella typhi causes typhoid fever, which is characterized by a more gradual onset of symptoms and is not typically associated with rapid onset gastroenteritis.
• Vibrio cholerae: Vibrio cholerae causes cholera, which is characterized by profuse watery diarrhea but usually has a longer incubation period than 4-6 hours.
• E. coli: While certain strains of Escherichia coli can cause foodborne illnesses, the rapid onset and severity described in the scenario are not typical for most E. coli infections.

Answer: Staphylococcus aureus

Staphylococcus aureus is a bacterium that produces toxins leading to symptoms like diarrhea and vomiting within a few hours of ingesting contaminated food. This rapid onset of symptoms is characteristic of Staphylococcal food poisoning.

The other options are incorrect:

• Salmonella typhi: Salmonella typhi causes typhoid fever, which is characterized by a gradual onset of symptoms such as high fever, abdominal pain, and constipation. It does not typically cause rapid diarrhea and vomiting.
• Vibrio cholerae: Vibrio cholerae is the bacterium responsible for cholera. Cholera is characterized by profuse watery diarrhea, often without vomiting, and has a longer incubation period than Ahmad’s symptoms (usually a day or more).
• E. coli: While some strains of E. coli can cause food poisoning, the symptoms are generally not as rapid as described in the scenario. E. coli infections may lead to abdominal cramps and bloody diarrhea, but vomiting is less common.

Answer: Clostridium perfringens

Clostridium perfringens is capsulated and shows a positive Negler’s reaction due to the presence of α-toxin. The Negler’s reaction is a biochemical test used to detect the production of lecithinase, and Clostridium perfringens is positive for this test.

The other options are incorrect:

• Clostridium tetani: This option forms spores but lacks the capsule and α-toxin, therefore won’t show a positive Negler’s reaction.
• Clostridium botulinum: This option doesn’t possess a capsule and produces neurotoxins, different from α-toxin, and hence doesn’t cause a positive Negler’s reaction.
• Clostridium difficile: This option also lacks a capsule and produces toxins A and B, again not α-toxin, and doesn’t trigger a positive Negler’s reaction

Answer: Pasteurella multocida

A Giemsa-stained blood smear with bipolar-staining pathogens indicates the involvement of Pasteurella multocida. This staining pattern is characteristic of Gram-negative coccobacilli, and Pasteurella multocida is one of the bacteria that exhibits bipolar staining under microscopic examination.

The other options are incorrect:

• Bacillus anthracis: Bacillus anthracis is a Gram-positive, spore-forming bacterium. It does not exhibit bipolar staining. Anthrax, caused by Bacillus anthracis, typically presents with non-bipolar staining bacteria.
• Brucella abortus: Brucella abortus is a Gram-negative bacterium, but it does not exhibit bipolar staining. Brucella species are small coccobacilli that do not show bipolar staining on microscopic examination.
• Mycobacterium bovis: Mycobacterium bovis is a slow-growing, acid-fast bacterium. It does not exhibit bipolar staining. Acid-fast staining is commonly used for the identification of mycobacteria, but it does not result in bipolar staining.

Answer: Number, length and direction of force

Both cilia and flagella are composed of microtubules arranged in a 9+2 pattern.
Basal bodies anchor both structures and are similar in location and length.
Both can have similar microtubule fusion patterns.
The key difference lies in their functions, achieved through distinct movement patterns. Cilia beat in coordinated, wave-like motions, while flagella have strong, whip-like strokes. The difference in number, length, and direction of these forces translates to their distinct types of movement.

The other options are incorrect:

• Arrangement of microtubules: Both have the same 9+2 arrangement of microtubules.
• Length and location of basal bodies: Both have similarly anchored basal bodies.
• How the microtubules are fused to each other: Fusion patterns can vary within cilia and flagella types, not between them.

Answer: Endotoxin

All Gram-negative bacilli have endotoxin. Endotoxin is a component of the outer membrane of Gram-negative bacteria and is released when the bacteria are lysed. It is a lipopolysaccharide (LPS) complex and can induce a strong immune response.

The other options are incorrect:

• Capsule: Not all Gram-negative bacilli have capsules. Capsules are polysaccharide layers some bacteria produce outside their cell wall, and their presence varies depending on the species and conditions.
• Exotoxin: While some Gram-negative bacteria produce exotoxins (protein toxins secreted into the surrounding environment), it’s not a universal feature. Many non-toxin-producing strains exist.
• Coagulase: Coagulase is an enzyme specific to certain Gram-positive bacteria like Staphylococcus aureus, allowing them to clot blood plasma for immune evasion. It’s not present in Gram-negative bacilli.

Answer: Proteus mirabilis

Proteus mirabilis is considered an opportunistic pathogen. Opportunistic pathogens are typically harmless in healthy individuals but can cause infections in weakened or compromised hosts, such as those with a compromised immune system or underlying medical conditions. Proteus mirabilis is commonly associated with urinary tract infections in individuals with predisposing factors.

The other options are incorrect:

• Salmonella Typhimurium: Salmonella Typhimurium is a pathogenic bacterium that can cause gastroenteritis in humans. It is not generally considered an opportunistic pathogen.
• Escherichia coli: Escherichia coli (E. coli) is a normal component of the human gut microbiota, and while some strains can cause infections, it is not typically considered an opportunistic pathogen.
• Yersinia pestis: Yersinia pestis is the causative agent of plague. It is not considered an opportunistic pathogen but rather a pathogen that can cause severe disease in healthy individuals.

Answer: Glucose fermentation with gas and H2S production

If the result of the Triple Sugar Iron (TSI) test shows a red/yellow slant with bubbles and a black precipitate in the butt, the interpretation is glucose fermentation with gas and hydrogen sulfide (H2S) production. The red/yellow color indicates the fermentation of glucose, the bubbles suggest the production of gas, and the black precipitate in the butt indicates the production of hydrogen sulfide.

The other options are incorrect:

• Glucose fermentation and H2S production: This option does not account for the gas production observed in the test. The correct interpretation includes both glucose fermentation and gas production.
• Lactose fermentation with gas and H2S production: The test result does not indicate lactose fermentation. The red/yellow color specifically suggests glucose fermentation. Lactose fermentation would have a different color reaction.
• Glucose fermentation and H2S production: This option does not account for the gas production observed in the test. The correct interpretation includes both glucose fermentation and gas production, along with H2S production.

Answer: Bacillus anthracis

Bacillus anthracis is a Gram-positive, spore-forming bacterium notorious for its extreme resistance to harsh environmental conditions, including antibiotics and disinfectants. This characteristic primarily stems from its robust endospore formation, which encases the bacterial DNA in a multi-layered, protective coat. This allows it to survive for decades in soil, withstand extreme temperatures and pressures, and resist common decontamination procedures.

The other options are incorrect:

• Pseudomonas aeruginosa: While Pseudomonas aeruginosa exhibits multidrug resistance and can be challenging to treat, its resistance pales in comparison to Bacillus anthracis’s near-impermeability to antibiotics and disinfectants.
• Clostridium tetani: Similarly, Clostridium tetani possesses some degree of resistance due to its spore-forming ability, but it remains susceptible to several antibiotics and readily succumbs to standard sterilization methods.
• Salmonella Typhimurium: This Gram-negative bacterium lacks spore formation and is generally susceptible to a wide range of antibiotics and disinfectants.

Answer: Infection by inhalation requires small number of pathogens

Brucella mallei, the causative agent of glanders, is classified as a Category B bioterror agent due to several factors, but the primary reason is its low infectious dose through inhalation. This means that even a small number of aerosolized B. mallei bacteria can cause severe and potentially fatal infections in humans and animals.

The other options are incorrect:

• It causes chronic disease in equines: While glanders can be chronic in horses, this characteristic alone doesn’t necessitate its classification as a bioterrorism threat.
• It presents as nasal and cutaneous forms: The various forms of glanders, including nasal and cutaneous, are important for diagnosis and treatment, but not directly related to its bioterrorism potential.
• Disease leads to formation of nodules on the skin: Skin nodules are a symptom of glanders, but not a defining feature for bioterrorism classification.

Answer: Listeria monocytogenes

Listeria monocytogenes is a Gram-positive, facultative intracellular bacterium found in soil, water, and various unpasteurized food products. While relatively mild in healthy adults, Listeria infection can pose serious risks to certain vulnerable populations, including pregnant women, newborns, the elderly, and immunocompromised individuals.

The other options are incorrect:

• Clostridium tetani: While tetanus can be fatal, it primarily affects the nervous system and causes muscle spasms. It doesn’t commonly lead to abortion or neonatal complications.
• Klebsiella pneumoniae: Although Klebsiella can cause pneumonia and other infections, it doesn’t specifically target pregnant women or have a high fatality rate in neonates.
• Mycoplasma mycoides: This bacterium primarily causes contagious bovine pleuropneumonia (CBPP) in cattle and is not typically associated with human infections, especially not with the mentioned complications.

Answer: Actinomyces bovis

Lumpy jaw, also known as actinomycosis, is a chronic, granulomatous infection primarily affecting cattle and swine. It’s characterized by the formation of abscesses and draining sinuses, often containing small, yellowish granules resembling sulfur. These granules are a diagnostic hallmark of the disease and contain the causative agent, Actinomyces bovis.

The other options are incorrect:

• Borrelia anserina: This spirochete causes Lyme disease in birds and humans, not lumpy jaw in animals. It doesn’t form abscesses or sulfur granules.
• Actinobacillus lignieresii: While this bacterium causes bovine purulent bronchopneumonia, it doesn’t affect the jaw or present with sulfur granules.
• Mycoplasma bovis: This organism causes contagious bovine pleuropneumonia, a respiratory disease in cattle. It doesn’t form lumpy jaw or sulfur granules.

Answer: Incomplete establishment of normal microbiota

Incomplete establishment of normal microbiota is NOT a predisposing factor for enterotoxaemia in elder sheep. Enterotoxaemia, also known as pulpy kidney disease, is caused by the bacterium Clostridium perfringens type D. Predisposing factors include sudden dietary changes, especially gorging on energy-rich diets, which promote the growth of the bacteria and toxin production leading to the disease.

The other options are incorrect:

• Abrupt change to a rich diet: An abrupt change to a rich diet is a predisposing factor for enterotoxaemia. Sudden exposure to a diet high in energy, particularly grains, can disrupt the balance of the microbial population in the gut, allowing Clostridium perfringens to proliferate.
• Gorging on energy-rich diet: Gorging on an energy-rich diet is a known predisposing factor for enterotoxaemia. Overeating of grains or other energy-rich feed can lead to an imbalance in the gut microbiota, promoting the growth of Clostridium perfringens.
• Intestinal hypomotility: Intestinal hypomotility, or reduced intestinal movement, is a predisposing factor for enterotoxaemia. Sluggish intestinal motility can contribute to the overgrowth of Clostridium perfringens in the gut.

Answer:

The TSI test (Triple Sugar Iron Agar) is specifically designed to determine a bacterium’s ability to ferment various sugars (glucose, lactose, and sucrose), its ability to produce hydrogen sulfide (H₂S), and its ability to reduce ferric iron (Fe³⁺) to ferrous iron (Fe²⁺). This combination of information makes it ideal for identifying and differentiating different bacterial species.

The other options are incorrect:

• Voges Proskauer test: This test detects the production of acetoin, an intermediate product in certain types of glucose fermentation. While some bacteria that perform a specific type of glucose fermentation (mixed acid fermentation) will also produce acetoin, the Voges Proskauer test is not a direct indicator of overall glucose fermentation capabilities.
• Catalase test: This test determines if a bacterium produces the enzyme catalase, which breaks down hydrogen peroxide (H₂O₂). Although some bacteria that ferment glucose also produce catalase, this test focuses on a different metabolic pathway and doesn’t provide information on glucose fermentation itself.
• Coagulase test: This test evaluates whether a bacterium produces coagulase, an enzyme that clots fibrinogen in blood plasma. It has no direct relation to glucose fermentation and is used to identify staphylococcal species specifically.

Answer: Mycobacterium bovis

Zoonotic cases of tuberculosis (TB) are usually associated with Mycobacterium bovis. This bacterium is closely related to Mycobacterium tuberculosis, which primarily infects humans, but M. bovis has a broader host range and can infect various mammals, including cattle. Humans can contract TB through the consumption of contaminated milk or direct contact with infected animals.

The other options are incorrect:

• Mycobacterium tuberculosis: This is the main culprit behind “human TB,” usually transmitted person-to-person through respiratory droplets. However, it can rarely infect animals, including cattle.
• Mycobacterium avium: This species can cause TB in humans, particularly those with compromised immune systems, but it’s mainly associated with birds and environmental exposure.
• Mycobacterium caprae: This type is extremely rare and primarily affects goats. While technically zoonotic, human infections are virtually unheard of.

Answer: Campylobacter fetus subsp. venerealis

The causative agent of bovine reproductive disease is Campylobacter fetus subsp. venerealis. This bacterium is specifically associated with bovine venereal campylobacteriosis, a sexually transmitted infection in cattle that can lead to reproductive problems, including infertility and abortion.

The other options are incorrect:

• Campylobacter fetus subsp. fetus: Campylobacter fetus subsp. fetus is associated with abortion in sheep and cattle. However, in the context of bovine reproductive disease, Campylobacter fetus subsp. venerealis is the more relevant pathogen.
• Campylobacter coli: Campylobacter coli is commonly associated with human gastroenteritis. It is not a primary causative agent of bovine reproductive disease.
• Campylobacter jejuni: Campylobacter jejuni is a common cause of human gastroenteritis and is not typically associated with bovine reproductive disease.

Answer: They produce endotoxin.

Anthrax bacilli, also known as Bacillus anthracis, are not classified as true endotoxin producers. They primarily release exotoxins, highly potent protein toxins responsible for the severe symptoms of anthrax disease. These exotoxins, Lethal Factor, Edema Factor, and Protective Antigen, work together to disrupt host cell functions and cause tissue damage.

The other options are incorrect:

• They are spore-forming: Anthrax bacilli are indeed spore-forming bacteria, a defining characteristic that allows them to persist in harsh environments for extended periods, contributing to their potential as biological weapons.
• They have a polypeptide capsule: Anthrax bacilli possess a capsule composed of polyglutamic acid, a polypeptide. This capsule plays a crucial role in evading the host immune system during infection.
• They produce non-hemolytic colonies: Anthrax colonies on sheep blood agar typically appear grayish-white and non-hemolytic, meaning they don’t break down red blood cells and cause a clear zone around the colony.

Answer: Exotoxin

Shiga toxin is a potent exotoxin produced by certain types of bacteria, primarily Shigella dysenteriae and some strains of Escherichia coli (STEC). Exotoxins are protein toxins actively secreted by bacteria into the surrounding environment, where they interact with host cells and disrupt their functions. In the case of Shiga toxin, it inhibits protein synthesis in eukaryotic cells, leading to cell death and tissue damage.

The other options are incorrect:

• Endotoxin: Endotoxins are lipopolysaccharides (LPS) found in the outer membrane of Gram-negative bacteria. They are released upon cell death and lysis, not actively secreted. While endotoxins can trigger inflammatory responses, they don’t have the same specific targeting and toxicity as Shiga toxin.
• Neurotoxin: Neurotoxins specifically target nerve cells, disrupting their function and causing neurological symptoms. Shiga toxin primarily affects intestinal epithelial cells and endothelial cells, not neurons.
• Exfoliative toxin: Exfoliative toxins cause skin or mucosal membrane shedding, leading to blistering and peeling. Shiga toxin doesn’t cause such exfoliative effects.

Answer: Ciprofloxacin

Ciprofloxacin is not commonly used to treat dermatophytosis (fungal disease) in cats and dogs. It is an antibiotic that belongs to the fluoroquinolone class and is primarily effective against bacterial infections, not fungal infections.

The other options are incorrect:

• Itraconazole: This is a potent antifungal medication commonly used to treat various fungal infections in animals, including dermatophytosis. It effectively targets and eliminates the fungal species responsible for the disease.
• Fluconazole: Similar to itraconazole, fluconazole is another antifungal agent effective against dermatophytes. It’s a readily available option for treating fungal infections in pets.
• Terbinafine: This is another fungicidal drug with excellent activity against dermatophytes. It’s frequently used topically or orally to treat fungal infections in cats and dogs.

Answer: Motile

While motility is a common characteristic of many Enterobacteriaceae members, it is not universal. Some species, like Salmonella typhi and Shigella dysenteriae, are non-motile. This means they lack flagella, the hair-like appendages that enable bacteria to move.

The other options are incorrect:

• Gram-negative: All members of Enterobacteriaceae are indeed Gram-negative bacteria. This means they have a cell wall structure with an outer membrane containing lipopolysaccharides (LPS), giving them a pink color when stained by Gram’s method.
• Catalase positive: All Enterobacteriaceae possess the enzyme catalase, which breaks down hydrogen peroxide (H₂O₂) into water and oxygen. This characteristic helps them tolerate environments with reactive oxygen species and is a useful tool for identification in the laboratory.
• Facultative anaerobes: Enterobacteriaceae are facultative anaerobes, meaning they can grow with or without oxygen. They can switch between aerobic respiration (using oxygen) and anaerobic respiration (using alternative electron acceptors) depending on the availability of oxygen in their environment.

Answer: Ixodes

Borrelia burgdorferi, the bacterium that causes Lyme disease, is transmitted by ticks of the genus Ixodes. The primary vector for Lyme disease is the black-legged tick, Ixodes scapularis, in North America, and Ixodes ricinus in Europe.

The other options are incorrect:

• Aedes: Aedes mosquitoes are known vectors for various diseases, including dengue and Zika, but they are not associated with the transmission of Borrelia burgdorferi.
• Anopheles: Anopheles mosquitoes are primarily known as vectors for the transmission of Plasmodium parasites, causing malaria. They are not involved in the transmission of Lyme disease.
• Argus: There is no widely recognized vector called Argus in the context of Lyme disease transmission or other major vector-borne diseases.

Answer: Both ‘Mycobacterium tuberculosis’ & ‘Mycobacterium avium’

Glycerol can indeed enhance the growth of both Mycobacterium tuberculosis and Mycobacterium avium. Here’s why:

Mycobacterium tuberculosis: Glycerol serves as a readily available carbon and energy source for M. tuberculosis, leading to increased replication and growth. Studies have shown that adding glycerol to culture media can significantly enhance M. tuberculosis yields.
Mycobacterium avium: Similar to M. tuberculosis, M. avium can readily utilize glycerol for growth and metabolism. Glycerol supplementation has been found to promote M. avium growth in various culture conditions.

The other options are incorrect:

Mycobacterium bovis: While M. bovis can also metabolize glycerol to some extent, the growth-promoting effect is not as pronounced as in M. tuberculosis and M. avium. Therefore, glycerol wouldn’t be the most significant factor influencing its growth compared to the other two options.

Answer: Clostridium botulinum

Clostridium botulinum is the bacterium that causes food intoxication. The intoxication results from the ingestion of botulinum toxin, which is produced by the bacterium under anaerobic conditions. Botulinum toxin is a potent neurotoxin that can cause paralysis and other symptoms when ingested with contaminated food.

The other options are incorrect:

• Clostridium tetani: Clostridium tetani is the bacterium responsible for causing tetanus, a condition characterized by muscle stiffness and spasms. Tetanus is not associated with food intoxication.
• Streptococcus pyogenes: Streptococcus pyogenes is associated with various infections, including strep throat and skin infections. It is not a common cause of food intoxication.
• Salmonella Typhimurium: Salmonella Typhimurium is a bacterium that causes foodborne infections rather than food intoxication. Infections with Salmonella can lead to symptoms such as diarrhea, abdominal cramps, and fever.

Answer: Mycoplasma bovis

Mycoplasma bovis exhibits a unique colony morphology on agar plates. Their colonies appear fried-egg-like with a central opaque “yolk” surrounded by a translucent “white” periphery. This distinctive appearance is due to their specific growth pattern and lack of a true cell wall.

The other options are incorrect:

• Klebsiella pneumoniae: While Klebsiella colonies can vary in appearance depending on the medium and conditions, they typically don’t resemble a fried egg. They often appear flat, mucoid, or wrinkled.
• Bacillus anthracis: Bacillus anthracis colonies are usually rough, dry, and grayish-white, lacking the central and peripheral zones characteristic of the “egg-fried” appearance.
• Mycobacterium bovis: Mycobacterium bovis colonies grow slower than Mycoplasma bovis and typically appear smooth, waxy, and creamy white, not resembling a fried egg.

Answer: Salmonella Gallinarum

Fowl typhoid is caused by Salmonella Gallinarum. It is a bacterial infection that affects poultry, particularly chickens, and can lead to systemic illness with symptoms such as lethargy, diarrhea, and high mortality rates in affected flocks.

The other options are incorrect:

• Salmonella Typhimurium: This serovar is more commonly associated with human foodborne illnesses and can occasionally infect poultry, but it doesn’t cause fowl typhoid.
• Salmonella Pullorum: This serovar is responsible for pullorum disease, another septicemic disease in poultry, but it’s clinically distinct from fowl typhoid and primarily affects chicks and poults.
• Salmonella Enteritidis: This serovar is another common cause of human foodborne illness but rarely causes disease in poultry and wouldn’t be associated with fowl typhoid.

Answer: It can grow at refrigerator temperatures (4°C)

Listeriosis, the disease caused by Listeria monocytogenes, is a major concern in food safety because of its ability to grow at low temperatures. This includes temperatures commonly found in refrigerators (4°C). This characteristic makes it crucial to maintain proper hygiene and storage practices to prevent food contamination and subsequent growth of the bacteria.

The other options are incorrect:

• It is an extracellular pathogen: Listeria monocytogenes can be both an intracellular and extracellular pathogen, depending on the host cell and the specific strain.
• It is non-motile: While some strains are non-motile, others possess flagella and exhibit motility.
• After Gram-staining, it exhibits G+ large bacilli: Listeria monocytogenes is a Gram-positive rod-shaped bacterium, not a large bacillus.

Answer: Microsporum canis

Dermatophytosis in humans, contracted from infected cats, is commonly caused by Microsporum canis. Microsporum canis is a fungus that can infect the skin, hair, and nails, leading to dermatophytosis or ringworm. Cats, particularly kittens, are known carriers of this fungus.

The other options are incorrect:

• Trychophyton canis: While this species can also cause dermatophytosis in humans, it’s more commonly associated with soil and rarely transmitted directly from cats.
• Microsporum capri: This species mainly infects goats and doesn’t play a significant role in human dermatophytosis.
• Epidermyphyton canis: This genus rarely causes skin infections in humans and isn’t associated with transmission from cats.

Answer: Polymerase chain reaction

Polymerase chain reaction (PCR) is not a serological test; it is a molecular biology technique used to amplify and analyze DNA. Serological tests detect antibodies or antigens in blood serum, while PCR directly amplifies and analyzes DNA.

The other options are incorrect:

• Rose-Bengal plate test: This is a rapid and sensitive agglutination test used for screening for bovine brucellosis in serum or milk samples.
• Brucella milk ring test: This is a simple and inexpensive screening test for detecting antibodies to Brucella in milk samples.
• Complement fixation test: This is a more confirmatory serological test for bovine brucellosis, offering high specificity and sensitivity.

Answer: Actinobacillus lignieresii

Wooden tongue, or timber tongue, with a history of grazing rough pasture indicates an infection by Actinobacillus lignieresii. This bacterium is the causative agent of a condition known as actinobacillosis, characterized by the formation of abscesses and fibrous lesions in the tongue and surrounding tissues of cattle.

The other options are incorrect:

• Borrelia anserina: Borrelia anserina is a spirochete bacterium that is primarily associated with avian hosts and causes fowl spirochetosis. It is not the causative agent of wooden tongue in cattle.
• Actinomyces bovis: Actinomyces bovis is associated with lumpy jaw disease in cattle, not wooden tongue. It causes chronic, suppurative infections in the tissues, often resulting in the formation of abscesses.
• Mycoplasma bovis: Mycoplasma bovis is a bacterium associated with respiratory and joint infections in cattle. It is not the causative agent of wooden tongue.

Answer: All of these

Fungi can indeed cause disease in humans and animals through multiple mechanisms, not just one. Here’s how each option plays a role:

• Tissue invasion: Some fungi directly invade and damage host tissues, causing localized infections or systemic disease depending on the species and location. Examples include invasive candidiasis, aspergillosis, and mucormycosis.
• Toxin production: Many fungi produce various toxins that contribute to disease pathogenesis. These toxins can have diverse effects, from damaging cells and disrupting organ function to triggering immune responses and inflammation. Examples include aflatoxins (produced by Aspergillus flavus), ergot alkaloids (produced by Claviceps purpurea), and trichothecenes (produced by Fusarium species).
• Induction of hypersensitivity: Certain fungi can trigger allergic reactions in individuals sensitized to their components. This can manifest as allergic rhinitis, asthma, or skin reactions depending on the allergen and exposure route. Examples include allergic bronchopulmonary aspergillosis and dermatophytosis (ringworm) caused by Trichophyton species.

Answer: All of these

Cryptococcus neoformans boasts several key virulence factors that contribute to its ability to cause disease, and all three listed options play a significant role:

• Capsule: The polysaccharide capsule surrounding C. neoformans acts as a shield, protecting the fungus from phagocytosis by immune cells and allowing it to evade the host’s immune response.
• Ability to grow at mammalian body temperature: C. neoformans can thrive at 37°C, the human body temperature, enabling it to establish itself within the warm environment of the host.
• Production of phenol oxidase: This enzyme catalyzes the production of melanin, a pigment with antioxidant and stress-protective properties. Melanin also helps C. neoformans resist antifungal drugs and contributes to its virulence by scavenging free radicals generated by the host’s immune response.

Answer: Mycoplasma bovis

As explained above, Mycoplasma bovis is the only organism among the listed options that lacks a cell wall. This unique characteristic contributes to its distinct pathogenicity and complicates antibiotic treatment due to its enhanced ability to evade the host’s immune system and certain antimicrobial agents.

The other options are incorrect:

• Actinomyces bovis: Actinomyces bovis is a bacterium with a cell wall. It is associated with lumpy jaw disease in cattle.
• Mycobacterium bovis: Mycobacterium bovis is a bacterium known for its complex cell wall structure, rich in mycolic acids. It has a cell wall.
• Borrelia anserina: Borrelia anserina is a spirochete bacterium and has a cell wall. It is associated with avian hosts.

Answer: Obligate anaerobe

The most common bacteria responsible for gas gangrene belong to the genus Clostridium, specifically Clostridium perfringens. These bacteria strictly require an anaerobic environment (absence of oxygen) for growth and multiplication. In the anaerobic environment of injured tissues deprived of oxygen, Clostridium perfringens thrives and produces potent toxins that cause tissue damage and gas production, characteristic of gas gangrene.

The other options are incorrect:

• Facultative anaerobe: These organisms can grow with or without oxygen. While some Clostridium species are facultative anaerobes, the gas gangrene-causing strains are obligate anaerobes.
• Microaerophilic: These organisms require low oxygen concentrations for growth. Again, gas gangrene-causing Clostridium species don’t tolerate even minimal oxygen levels and are obligate anaerobes.
• Obligate aerobe: These organisms require oxygen for growth and cannot survive in its absence. Gas gangrene bacteria, as mentioned, strictly require an anaerobic environment.

Answer: Contact with urine from infected animal

Leptospira, the bacterium responsible for leptospirosis, is primarily transmitted to humans through contact with urine from infected animals. Leptospires are shed in the urine of infected animals, contaminating the environment. Humans can become infected through direct contact with contaminated water, soil, or surfaces, especially mucous membranes or broken skin.

The other options are incorrect:

• Animal scratch: While animal scratches can theoretically transmit Leptospira if there’s contact with infected animal urine on the claws, it’s a less common and less significant route compared to direct contact with urine.
• Animal bite: Although animal bites can transmit other diseases, Leptospira isn’t typically transmitted this way. The bacteria are primarily shed in the urine, not saliva.
• Arthropod vector: Some specific Leptospira strains can be transmitted by blood-sucking arthropods like rodents and mosquitoes, but this type of transmission is less common in human cases compared to direct contact with contaminated urine.

Answer: Fusarium species

Zearalenone, a potent estrogenic mycotoxin, is primarily produced by Fusarium species. This genus of filamentous fungi includes various plant pathogens known for their ability to produce a diverse range of mycotoxins, including zearalenone.

The other options are incorrect:

• Aspergillus species: While some Aspergillus species can produce other mycotoxins, they are not known for producing zearalenone.
• Penicillium species: Penicillium species are primarily known for their antibiotic production and are not associated with zearalenone production.
• Claviceps species: Claviceps species can produce ergot alkaloids, a different type of mycotoxin, but not zearalenone.

Answer: Robertson cooked-meat medium

Robertson cooked-meat medium is an example of an anaerobic medium. It is used for the cultivation of anaerobic bacteria, which are organisms that thrive in the absence of oxygen. The medium is prepared by cooking meat, which removes the oxygen and creates an environment suitable for the growth of anaerobes.

The other options are incorrect:

• Sabouraud dextrose agar: This medium supports the growth of fungi, but it’s not designed for anaerobes and provides an aerobic environment.
• MacConkey agar: This medium is used for isolating and differentiating Gram-negative bacteria, and it also provides an aerobic environment.
• Mannitol salt agar: This medium is used for detecting Staphylococcus aureus, which is a facultative anaerobe capable of growing in both aerobic and anaerobic conditions. While it can support some anaerobic growth, it’s not specifically designed for obligate anaerobes.

Answer: Differential medium

MacConkey agar is an example of a differential medium. It is specifically designed to differentiate between lactose-fermenting and non-lactose-fermenting Gram-negative bacteria. The medium contains lactose, neutral red dye, and crystal violet. Lactose-fermenting bacteria produce acid, causing a color change in the colonies, while non-lactose fermenters do not change color.

The other options are incorrect:

• General purpose medium: While MacConkey agar can support the growth of a variety of Gram-negative bacteria, it’s not considered a general purpose medium as its selective and differential properties limit its use to specific applications.
• Enrichment medium: Enrichment media are designed to favor the growth of specific target organisms by providing additional nutrients or suppressing competing bacteria. MacConkey agar doesn’t primarily aim to increase bacterial growth but to differentiate them based on a specific metabolic property.
• Enriched medium: Enriched media contain additional nutrients like blood or serum to support the growth of fastidious bacteria with more demanding nutritional requirements. MacConkey agar, while containing nutrients, isn’t specifically categorized as an enriched medium.

Answer: Urethritis

Mycoplasma genitalium and Mycoplasma hominis are the primary species associated with urethritis, particularly in sexually active individuals. These species can infect the urethra, causing inflammation and symptoms like pain during urination, frequent urination, and discharge.

The other options are incorrect:

• Meningitis: While Mycoplasma pneumoniae can rarely cause meningitis, it’s a much less common complication compared to urethritis.
• Prosthetic heart valve: Mycoplasma infections in prosthetic heart valves are also uncommon, although they can occur in immunocompromised individuals.
• Septic arthritis: Mycoplasma can occasionally cause septic arthritis, but it’s again a rare complication and less frequent than urethritis.

Answer: Ciprofloxacin

The current preferred antimicrobial treatment for cutaneous anthrax is ciprofloxacin. Ciprofloxacin is a fluoroquinolone antibiotic that is effective against Bacillus anthracis, the bacterium causing anthrax. Other fluoroquinolones, such as levofloxacin, are also considered effective alternatives.

The other options are incorrect:

• Aminoglycosides: While effective against anthrax, they are typically reserved for severe cases or when fluoroquinolones are contraindicated due to potential ototoxicity and nephrotoxicity.
• Penicillin: Penicillin G was historically the first-line treatment for anthrax, but its activity is bacteriostatic (stops growth) and requires intravenous administration, making fluoroquinolones a more favorable choice for uncomplicated cases.
• Tetracycline: Although effective against anthrax, tetracyclines have some limitations like potential interactions with other medications and side effects like photosensitivity, reducing their preference compared to fluoroquinolones.

Answer: A polypeptide capsule

Bacillus anthracis is unique among bacteria as it possesses a polypeptide capsule. The capsule is composed of a protein called poly-D-glutamic acid. This capsule is a key virulence factor for Bacillus anthracis, providing protection against phagocytosis by the host’s immune cells.

The other options are incorrect:

• An endotoxin: Endotoxins are lipopolysaccharides found in the outer membrane of Gram-negative bacteria. Bacillus anthracis is Gram-positive and doesn’t possess an endotoxin.
• A polysaccharide capsule: While many bacteria do possess polysaccharide capsules, Bacillus anthracis distinguishes itself by having a unique polypeptide capsule.
• Teichoic acid in its outer cell wall: Teichoic acid is another component of the cell wall in many Gram-positive bacteria, including Bacillus anthracis. However, its presence is not unique to this specific bacterium.

Answer: Ehrlichiosis

Ehrlichiosis is a disease that can be transmitted by ticks. It is caused by various species of bacteria belonging to the genus Ehrlichia, which are primarily transmitted to humans through the bite of infected ticks.

The other options are incorrect:

• Q fever: This disease is primarily caused by Coxiella burnetii, a bacterium transmitted through inhalation of contaminated aerosols, not by ticks.
• Leptospirosis: While some Leptospira species can survive in ticks, the primary mode of transmission for this bacterial infection is contact with infected animal urine or contaminated water, not tick bites.
• Yellow fever: This viral disease is transmitted by mosquitoes, not ticks.

Answer: 107.6°F (42°C) microaerophilic Skirrow medium

Campylobacter jejuni is a microaerophilic bacterium, which means it grows best in low-oxygen conditions. Therefore, the special laboratory conditions needed to recover C. jejuni include a temperature of 42°C (107.6°F) and a microaerophilic environment. Skirrow medium is a selective medium containing antibiotics that inhibit the growth of other bacteria while allowing the growth of Campylobacter species.

The other options are incorrect:

• 98.6°F (37°C) aerobic blood agar plates: C. jejuni requires a higher temperature and reduced oxygen. Standard blood agar plates at 37°C and atmospheric oxygen wouldn’t be suitable.
• 98.6°F (37°C) anaerobic blood agar plates: While anaerobic conditions wouldn’t harm C. jejuni, the ideal environment is microaerophilic, not completely anaerobic. Additionally, blood agar might not be selective enough for optimal isolation.
• 107.6°F (42°C) anaerobic Skirrow medium: Although the temperature is correct, anaerobic conditions wouldn’t provide enough oxygen for C. jejuni’s microaerophilic requirements.

Answer: Enterococcus faecalis

The characteristics described in the question, including Gram-positive cocci, vancomycin resistance, PYR (pyrrolidonyl arylamidase) positivity, and the presence of Lancefield group D antigen, are indicative of Enterococcus faecalis. Enterococci, including E. faecalis, are Gram-positive cocci that belong to Lancefield group D. They are known for their resistance to vancomycin, and PYR testing is positive for Enterococcus species.

The other options are incorrect:

• Staphylococcus aureus: While Gram-positive cocci, they are typically arranged in clusters and not vancomycin-resistant as mentioned.
• Streptococcus pneumoniae: Diplococcal Gram-positive cocci, susceptible to vancomycin and not PYR-positive.
• Streptococcus agalactiae: Gram-positive cocci in chains, typically not vancomycin-resistant, and belongs to Lancefield group B.

Answer: Enterhemorrhagic E. coli (EHEC)

Verotoxin-producing Escherichia coli (VTEC) or Shiga toxin-producing E. coli (STEC), such as the O157:H7 serotype, belongs to the Enterohemorrhagic E. coli (EHEC) group. EHEC strains produce toxins known as Shiga toxins or verotoxins, which are associated with severe gastrointestinal illness, including bloody diarrhea and, in some cases, hemolytic uremic syndrome (HUS).

The other options are incorrect:

• Enteroaggregative E. coli (EAEC): These E. coli strains typically cause persistent, watery diarrhea through a different mechanism involving biofilm formation and adherence to the intestinal mucosa.
• Enteroinvasive E. coli (EIEC): These E. coli strains invade intestinal epithelial cells, mimicking Shigella bacteria, and cause dysentery-like symptoms with bloody diarrhea.
• Enterotoxigenic E. coli (ETEC): These E. coli strains produce heat-stable and heat-labile toxins that cause watery diarrhea through their effect on intestinal electrolyte and fluid secretion.

Answer: Urease production

A key typical characteristic that distinguishes Helicobacter pylori from Campylobacter species is urease production. H. pylori is known for its ability to produce urease, an enzyme that hydrolyzes urea to ammonia and carbon dioxide. This urease activity is one of the diagnostic features used for the identification of H. pylori in the laboratory.

The other options are incorrect:

• Coagulase production: Both H. pylori and Campylobacter species are Gram-negative and do not produce coagulase.
• Catalase production: Both H. pylori and Campylobacter species are catalase-positive, meaning they can break down hydrogen peroxide.
• Curved shape: Only Campylobacter species have a characteristic curved or spiral shape due to their polar flagella. H. pylori has rod-shaped morphology with multiple sheathed flagella.

Answer: Salmonella species

In a 4-year-old with fever and diarrhea, the growth of a Gram-negative rod in blood culture is most likely to be due to Salmonella species. Salmonella is a Gram-negative bacterium that can cause gastroenteritis, and it is commonly associated with foodborne infections leading to symptoms such as fever and diarrhea.

The other options are incorrect:

• Group B Streptococcus: While this Gram-positive organism can cause meningitis and sepsis in newborns, it’s less common in older children, and gastroenteritis isn’t typically a presenting symptom.
• Listeria species: These Gram-positive rods can cause meningitis and encephalitis but are more commonly associated with pregnant women, newborns, and immunocompromised individuals. They are not typical agents of childhood gastroenteritis.
• Neisseria species: These Gram-negative diplococci typically cause respiratory infections like meningitis or gonorrhea, and not gastroenteritis.

Answer: Raw milk

Unpasteurized dairy products, especially milk and soft cheeses, are major reservoirs of L. monocytogenes. The bacteria can easily contaminate milk during milking and processing, posing a significant risk of infection for consumers if consumed raw.

The other options are incorrect:

• Human feces: While L. monocytogenes can be present in human feces, person-to-person transmission through fecal-oral route is relatively uncommon.
• Soil: L. monocytogenes can be found in soil and water, but direct ingestion of contaminated soil is an unlikely source of infection in most cases.
• Ticks: Ticks typically transmit other bacterial pathogens like Lyme disease bacteria, not L. monocytogenes.

Answer: Pilli

The ability of Neisseria meningitidis to colonize the respiratory mucosa is associated with its ability to synthesize pili (also known as fimbriae). Pili are hair-like appendages on the surface of bacteria that facilitate adhesion to host cells and mucosal surfaces. In the case of Neisseria meningitidis, pili play a crucial role in the initial attachment to respiratory mucosal cells, enabling the bacterium to establish colonization.

The other options are incorrect:

• Coagulase: This enzyme is not produced by Neisseria meningitidis and not involved in mucosal colonization.
• Collagenase: This enzyme degrades collagen, but isn’t directly involved in Neisseria meningitidis adhesion to mucosal epithelium.
• Lipases: These enzymes break down lipids, not relevant to the adhesion process and colonization of the respiratory mucosa

Answer: Produces a potent urease

UTI (urinary tract infection) caused by Proteus mirabilis facilitates the formation of kidney stones because the organism produces a potent urease. Urease is an enzyme that hydrolyzes urea, leading to the production of ammonia and carbon dioxide. The increase in ammonia can elevate the pH of the urine, resulting in the formation of struvite or triple phosphate kidney stones.

The other options are incorrect:

• Destroys blood vessels in the kidney: While Proteus mirabilis can contribute to inflammatory processes, direct blood vessel destruction isn’t the primary mechanism for kidney stone formation.
• Exhibits ‘swarming’ motility: This flagellar-based movement allows Proteus mirabilis to spread on moist surfaces but doesn’t directly contribute to stone formation.
• Ferments many sugars: This metabolic ability helps the bacteria survive in the urinary tract but doesn’t directly influence stone formation.