Bacteriology Practice Questions

Q: Malignant pustules are seen in:

Anthrax. ***Anthrax*** - Cutaneous anthrax, caused by *Bacillus anthracis*, presents with a characteristic **painless ulcer with a black eschar** (malignant pustule) and surrounding edema. - This lesion evolves from a papule to a vesicle, then to a necrotic ulcer or "malignant pustule." *Pemphigus* - Pemphigus is an **autoimmune blistering disease** characterized by fragile blisters and erosions on the skin and mucous membranes. - It does not involve "malignant pustules" but rather flaccid bullae due to acantholysis. *Tularemia* - Tularemia, caused by *Francisella tularensis*, can present with an **ulceroglandular lesion** at the site of inoculation, but this is typically a single, painful ulcer with regional lymphadenopathy, not a "malignant pustule." - The ulcer is often clean-based and lacks the characteristic black eschar seen in anthrax. *Actinomycosis* - Actinomycosis is a bacterial infection caused by *Actinomyces species*, commonly presenting as **chronic, suppurative abscesses** that form sinus tracts. - The lesions are characterized by granulomas and "sulfur granules" in the pus, not "malignant pustules."

Q: A sexually active 25-year-old man develops epididymitis and orchitis. Needle biopsy demonstrates a prominent leukocytic infiltrate with numerous neutrophils. Which of the following organisms is the most likely cause of this man's infection?

Neisseria gonorrhoeae. ***Neisseria gonorrhoeae*** - In a sexually active man under 35, **Neisseria gonorrhoeae** is a common cause of epididymitis and orchitis, often manifesting with a prominent **neutrophilic infiltrate**. - This organism is a **Gram-negative diplococcus** that causes gonococcal urethritis, which can ascend to cause epididymitis. *Pseudomonas sp* - **Pseudomonas** infections of the genitourinary tract are typically associated with **nosocomial infections**, indwelling catheters, or compromised immune systems. - While it can cause severe inflammation, it is less common in a healthy, sexually active young man without predisposing factors. *Escherichia coli* - **E. coli** is a common cause of epididymitis, particularly in men over 35 or those engaging in **anal intercourse**, often due to retrograde flow of infected urine. - While it can cause an inflammatory response, *Neisseria gonorrhoeae* is more prevalent in the described demographic for sexually transmitted infections. *Mycobacterium tuberculosis* - **Mycobacterium tuberculosis** causes granulomatous inflammation and typically presents with **caseating necrosis** and **giant cells** rather than a prominent neutrophilic infiltrate. - While it can cause chronic epididymitis, it causes a different histological picture and is less acute than described.

Q: Which of the following is the most common cause of subacute endocarditis?

Streptococcus viridans. ***Streptococcus viridans*** - This group of bacteria is the most frequent cause of **subacute bacterial endocarditis**, particularly in individuals with pre-existing valvular heart disease. - They typically cause a **slowly progressive infection** on damaged heart valves, often following dental procedures. *Staphylococcus epidermidis* - This bacterium is a common cause of **nosocomial infections** and endocarditis associated with **prosthetic heart valves** or intravascular devices. - While it can cause endocarditis, it is less common than *S. viridans* for native valve subacute endocarditis. *Streptococcus pyogenes* - *S. pyogenes* is known for causing pharyngitis ("strep throat"), cellulitis, and **rheumatic fever**, which can lead to valvular damage. - However, it is a rare direct cause of infective endocarditis. *Staphylococcus aureus* - This bacterium is a common cause of **acute infective endocarditis**, particularly in intravenous drug users and those with prosthetic valves or catheters. - It typically causes a **rapidly destructive infection** and is less commonly associated with the subacute form.

Q: True statement about diphtheria toxin is -

Toxin is phage mediated. ***Toxin is phage mediated*** - The diphtheria toxin gene (tox gene) is carried by a **bacteriophage (a bacterial virus)**, specifically a lysogenic bacteriophage called corynephage beta. - This means that *Corynebacterium diphtheriae* only produces the toxin if it has been infected by and integrated the DNA of this specific bacteriophage into its genome, a process known as **lysogenic conversion**. *Toxin acts by inhibiting synthesis of capsule* - The diphtheria toxin specifically inhibits **protein synthesis** in eukaryotic cells by inactivating **Elongation Factor 2 (EF-2)**. - It does not interfere with the synthesis of a bacterial capsule, which *Corynebacterium diphtheriae* typically does not possess. *Endotoxaemia causes systemic manifestation* - Diphtheria toxin is an **exotoxin**, meaning it is secreted by the live bacterium and causes systemic effects by entering the bloodstream. - **Endotoxins** are components of the outer membrane of gram-negative bacteria (specifically **Lipopolysaccharide or LPS**) that are released upon bacterial cell lysis, and *Corynebacterium diphtheriae* is a gram-positive bacterium. *Toxin is required for local infection* - While the toxin is critical for the **virulence and systemic manifestations** of diphtheria, the initial local infection (e.g., pseudomembrane formation in the throat) is primarily due to bacterial growth and inflammatory response. - The toxin's main role is to cause **tissue necrosis** at the infection site and lead to serious systemic effects like **myocarditis** and **neuropathy**.

Q: Which of the following organisms is commonly implicated in spontaneous bacterial peritonitis in patients of Nephrotic syndrome?

Streptococcus pneumoniae. ***Streptococcus pneumoniae*** - This organism is a common cause of **spontaneous bacterial peritonitis (SBP)** in patients with **nephrotic syndrome**, particularly in children. - Patients with nephrotic syndrome are prone to infections due to impaired immunity (e.g., loss of immunoglobulins in urine) and **ascites**, providing a favorable environment for bacterial growth. *Salmonella* - While Salmonella can cause opportunistic infections, it is **not commonly implicated** in spontaneous bacterial peritonitis in nephrotic syndrome. - Salmonella typically causes **gastroenteritis** and can lead to bacteremia, but peritoneal infection is less common without direct bowel perforation. *Hemophilus influenza* - *Haemophilus influenzae* is a significant pathogen, but it is **not typically a cause** of spontaneous bacterial peritonitis in nephrotic syndrome. - It is more commonly associated with **respiratory infections**, meningitis, and epiglottitis. *Staphylococcus* - **Staphylococcal species** are generally not the primary cause of spontaneous bacterial peritonitis in uncomplicated nephrotic syndrome. - While *Staphylococcus aureus* can cause peritonitis, particularly in patients on **peritoneal dialysis** or with other predisposing factors, it is less common in SBP associated with nephrotic syndrome compared to *Streptococcus pneumoniae*.

Q: The most virulent pathogenic Bacillus species is

Bacillus anthracis. ***Bacillus anthracis*** - This species is the **causative agent of anthrax**, a severe and often fatal disease in humans and animals, making it the most virulent. - Its virulence is attributed to its **capsule** and the production of **anthrax toxins** (edema factor, lethal factor, and protective antigen). *Bacillus cereus* - Primarily known for causing **food poisoning** (emetic and diarrheal types) due to preformed toxins in contaminated food. - While it can cause opportunistic infections, it is generally considered **less virulent** than *B. anthracis*. *Bacillus subtilis* - This is a common **soil bacterium** and is often used as a **probiotic** and in industrial applications. - It is generally considered **non-pathogenic** to humans, though rare opportunistic infections have been reported in immunocompromised individuals. *Bacillus megaterium* - A large, **spore-forming bacterium** found in soil and various environments. - It is largely **non-pathogenic** and is commonly used in industrial microbiology for enzyme production.

Q: A 36 years male presented with complaint of productive cough and fever for last 2 months. He has undergone kidney transplantation 2 years back. His sputum examination revealed a gram positive filamentous bacteria that showed acid fastness with modified Ziehl-Neelsen staining (1% H2SO4). The most likely etiological agent is ?

Nocardia asteroides. ***Nocardia asteroides*** - This patient, being an **immunocompromised kidney transplant recipient**, is highly susceptible to **opportunistic infections**. *Nocardia* species are **gram-positive, filamentous, branched bacteria** that are **weakly acid-fast** (positive with modified Ziehl-Neelsen staining, typically 1% H2SO4), commonly causing **pulmonary infections** with productive cough and fever. - Pulmonary nocardiosis can mimic tuberculosis or other fungal infections, and the acid-fast staining characteristic helps differentiate it from non-acid-fast filamentous bacteria like *Actinomyces*. *Blastomyces dermatitidis* - This is a **dimorphic fungus** that causes **blastomycosis**, an endemic infection in certain geographic regions, which is usually diagnosed by visualization of broad-based budding yeasts or culture. - It would not appear as a **gram-positive filamentous bacterium** with acid-fast properties in sputum. *Actinomyces israelii* - *Actinomyces israelii* is a **gram-positive, filamentous bacterium** that causes **actinomycosis**, often characterized by chronic abscesses, sinus tracts, and "sulfur granules." - Unlike *Nocardia*, *Actinomyces* species are **not acid-fast**, which rules it out given the staining results. *Cryptosporidium parvum* - This is a **protozoan parasite** that causes **cryptosporidiosis**, primarily manifesting as **gastroenteritis** (diarrhea), especially in immunocompromised individuals. - It would not present as a **filamentous bacterial form in sputum**, nor would it be diagnosed by Gram stain and acid-fast modified Ziehl-Neelsen staining in this context.

Q: A young lady complains of sore throat for 3 days along with fever and headache. On examination, she was severely dehydrated, her BP was found to be 90/ 50 mm Hg and on the distal aspect of the cuff, small red spots were noted. What could be the most probable etiological agent responsible for causing these symptoms -

Neisseria meningitidis. Neisseria meningitidis - The combination of sore throat, fever, headache, severe dehydration, hypotension, and petechiae (small red spots from broken capillaries, often seen with bleeding diathesis) is highly suggestive of meningococcemia [1]. - Neisseria meningitidis can cause fulminant sepsis and meningitis, leading to rapid progression of symptoms including DIC and widespread petechial rashes due to vasculitis [2]. Brucella suis - Brucellosis typically presents as an insidious illness with undulating fever, arthralgia, and organomegaly, not sudden onset severe symptoms with dehydration and petechiae. - While it can be severe, it does not commonly manifest with the acute, dramatic hemorrhagic signs seen in this patient. Brucella abortus - Similar to Brucella suis, Brucella abortus causes brucellosis, which is a chronic or subacute infection. - The clinical picture of acute onset, severe dehydration, hypotension, and petechiae points away from brucellosis. Staphylococcus aureus - Staphylococcus aureus can cause various infections, including sepsis, but a sore throat and the specific presentation of petechiae with hypotension following an apparent upper respiratory tract infection are less characteristic [3]. - While S. aureus can produce toxins leading to toxic shock syndrome, meningococcal sepsis is a more direct fit for the rapid onset and hemorrhagic signs.

Q: The animal model frequently used for M. leprae is -

Nine-banded armadillos. ***Nine-banded armadillos*** - **Nine-banded armadillos** are particularly susceptible to *Mycobacterium leprae* due to their unusually low body temperature (around 30-35°C), which is ideal for the growth of the bacterium. - They are the only other species known to naturally develop **leprosy**, making them an invaluable model for studying the disease and testing vaccines and treatments. *Rabbits* - Rabbits are generally not susceptible to *Mycobacterium leprae* infection and are not used as a primary animal model for leprosy research. - While some mycobacterial infections can be studied in rabbits, they do not mimic the human disease progression of leprosy. *Guinea pig* - Guinea pigs are known for their susceptibility to certain mycobacterial infections, particularly tuberculosis, but they are not a suitable model for *Mycobacterium leprae*. - The unique growth requirements and disease presentation of leprosy are not replicated in guinea pigs. *Mice* - While mice can be experimentally infected with *Mycobacterium leprae*, especially immunodeficient strains (e.g., nude mice, SCID mice), the infection in mice is often limited and does not fully mimic the natural human disease. - The **footpad infection model** in mice is used for drug screening but does not allow for widespread systemic infection characteristic of natural leprosy.

Q: Infective dose of S.typhi is

10³-10⁶ bacilli. ***10³-10⁶ bacilli*** - The **infective dose** for *Salmonella typhi* is generally considered to be in the range of **10³ to 10⁶ bacilli**, making it a relatively high dose required for infection. - This relatively high infective dose contributes to the epidemiology of typhoid fever, often requiring significant contamination for transmission. *10⁷-10¹² bacilli* - This range represents an **extremely high infective dose**, far exceeding the typical amount needed for *S. typhi* to cause infection. - Such a quantity would imply a much greater resistance to host defenses or a much lower virulence for the pathogen than observed. *10 bacilli* - An infective dose of **10 bacilli** is considered very low, characteristic of highly virulent pathogens like *Shigella* species. - *Salmonella typhi* is not typically associated with such a small infective dose, as it requires a larger inoculum to overcome host defenses. *10² bacilli* - An infective dose of **10² (100) bacilli** is still considered a relatively low dose for bacterial pathogens. - While some pathogens can cause infection with this number, *S. typhi* generally requires a larger inoculum to establish an infection and cause typhoid fever.

Question 1

Malignant pustules are seen in:

Accepted Answer

Anthrax

Answer

Pemphigus

Answer

Tularemia

Answer

Actinomycosis

Question 2

A sexually active 25-year-old man develops epididymitis and orchitis. Needle biopsy demonstrates a prominent leukocytic infiltrate with numerous neutrophils. Which of the following organisms is the most likely cause of this man's infection?

Accepted Answer

Neisseria gonorrhoeae

Answer

Pseudomonas sp

Answer

Escherichia coli

Answer

Mycobacterium tuberculosis

Question 3

Which of the following is the most common cause of subacute endocarditis?

Accepted Answer

Streptococcus viridans

Answer

Staphylococcus epidermidis

Answer

Streptococcus pyogenes

Answer

Staphylococcus aureus

Question 4

True statement about diphtheria toxin is -

Accepted Answer

Toxin is phage mediated

Answer

Toxin acts by inhibiting synthesis of capsule

Answer

Endotoxaemia causes systemic manifestation

Answer

Toxin is required for local infection

Question 5

Which of the following organisms is commonly implicated in spontaneous bacterial peritonitis in patients of Nephrotic syndrome?

Accepted Answer

Streptococcus pneumoniae

Answer

Salmonella

Answer

Hemophilus influenza

Answer

Staphylococcus

Question 6

The most virulent pathogenic Bacillus species is

Accepted Answer

Bacillus anthracis

Answer

Bacillus cereus

Answer

Bacillus subtilis

Answer

Bacillus megaterium

Question 7

A 36 years male presented with complaint of productive cough and fever for last 2 months. He has undergone kidney transplantation 2 years back. His sputum examination revealed a gram positive filamentous bacteria that showed acid fastness with modified Ziehl-Neelsen staining (1% H2SO4). The most likely etiological agent is ?

Accepted Answer

Nocardia asteroides

Answer

Blastomyces dermatitidis

Answer

Actinomyces israelii

Answer

Cryptosporidium parvum

Question 8

A young lady complains of sore throat for 3 days along with fever and headache. On examination, she was severely dehydrated, her BP was found to be 90/ 50 mm Hg and on the distal aspect of the cuff, small red spots were noted. What could be the most probable etiological agent responsible for causing these symptoms -

Accepted Answer

Neisseria meningitidis

Answer

Brucella suis

Answer

Brucella abortus

Answer

Staphylococcus aureus

Question 9

The animal model frequently used for M. leprae is -

Accepted Answer

Nine-banded armadillos

Answer

Rabbits

Answer

Guinea pig

Answer

Mice

Question 10

Infective dose of S.typhi is

Accepted Answer

10³-10⁶ bacilli

Answer

10⁷-10¹² bacilli

Answer

10 bacilli

Answer

10² bacilli

Bacteriology — MCQs

Bacteriology — MCQs

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