Bacteriology — MCQs

Bacteriology Indian Medical PG Practice Questions and MCQs

Question 2241: Hemorrhagic meningitis is caused by

A. Neisseria meningitidis
B. Bacillus anthracis (Correct Answer)
C. Haemophilus influenzae
D. Streptococcus pneumoniae

Explanation: ***Bacillus anthracis*** - *Bacillus anthracis* causes **anthrax meningitis**, which is characteristically **hemorrhagic** and rapidly fatal - Characterized by extensive **meningeal and brain parenchymal bleeding** with hemorrhagic CSF - This form of meningitis is specifically known for its **hemorrhagic nature** due to the toxins produced by the bacteria, leading to vascular damage and edema - Often presents as "cardinal's cap" appearance due to severe hemorrhagic involvement *Streptococcus pneumoniae* - *Streptococcus pneumoniae* is the most common cause of **bacterial meningitis** in adults - Typically causes **purulent meningitis** with neutrophilic infiltration, not hemorrhagic meningitis - While severe cases can have complications with vascular involvement, it is not characterized by hemorrhagic meningitis *Neisseria meningitidis* - *Neisseria meningitidis* is a common cause of **bacterial meningitis**, often presenting with petechial rash due to **vasculitis** - Can lead to **disseminated intravascular coagulation (DIC)** and purpura fulminans with hemorrhagic skin lesions - However, the meningitis itself is typically **purulent**, not grossly hemorrhagic *Haemophilus influenzae* - *Haemophilus influenzae* type b (Hib) was a major cause of **bacterial meningitis** before vaccination - Causes **purulent meningitis** with inflammation and pus formation, rather than significant hemorrhage within the meninges - Now rare due to effective vaccination programs

Question 2242: Causative organism for ANUG is:

A. Streptococcus sanguis
B. Treponema pallidum and spirochetes
C. Fusospirochetal complex (Correct Answer)
D. Staphylococcus epidermidis

Explanation: ***Fusospirochetal complex*** - **Acute Necrotizing Ulcerative Gingivitis (ANUG)**, also known as Vincent's angina or trench mouth, is caused by a synergistic polymicrobial infection involving **Fusobacterium species** (particularly F. nucleatum) and **oral spirochetes** (Borrelia vincentii and Treponema species). - This fusospirochetal complex creates a destructive, ulcerative inflammation of the gingiva, presenting with **painful, bleeding gums, punched-out papillae, pseudomembrane formation**, and characteristic **fetid breath**. - The condition typically occurs in patients with **poor oral hygiene, stress, immunosuppression**, or **malnutrition**. *Streptococcus sanguis* - This bacterium is a common commensal of the oral cavity and plays a role in **dental plaque formation** and initial colonization of tooth surfaces. - While present in the mouth, it is **not the causative agent** for the necrotizing lesions characteristic of ANUG. *Treponema pallidum and spirochetes* - **Treponema pallidum** specifically causes **syphilis**, a sexually transmitted infection, not ANUG. - While **oral spirochetes** (other Treponema and Borrelia species) are indeed critical components of ANUG, they work synergistically with **Fusobacterium**, hence the term "fusospirochetal complex." - This option is partially correct but incomplete and includes T. pallidum which is incorrect. *Staphylococcus epidermidis* - **Staphylococcus epidermidis** is a skin commensal organism implicated in **nosocomial infections** and biofilm formation on medical devices. - It has **no role** in the pathogenesis of ANUG.

Question 2243: Epiglottitis is mainly caused by:

A. Streptococcus
B. Staphylococcus
C. Mycoplasma
D. Haemophilus (Correct Answer)

Explanation: ***Haemophilus*** - **_Haemophilus influenzae_ type b (Hib)** was historically the leading cause of epiglottitis, especially in children, prior to widespread vaccination. - While other bacteria can cause epiglottitis, **_Haemophilus influenzae_** remains one of the most significant causative agents, particularly in unvaccinated populations or in adults. *Streptococcus* - Various species of **_Streptococcus_**, such as **_Streptococcus pneumoniae_** and **Group A _Streptococcus_ (GAS)**, can cause other upper respiratory tract infections like pharyngitis or pneumonia. - While they can occasionally be isolated in epiglottitis, they are **not the main cause** compared to Haemophilus. *Staphylococcus* - **_Staphylococcus aureus_** is a common cause of skin infections, abscesses, and some respiratory infections, such as pneumonia. - It is **rarely the primary pathogen** responsible for acute epiglottitis. *Mycoplasma* - **_Mycoplasma pneumoniae_** is a common cause of atypical pneumonia, often presenting with a more gradual onset and milder symptoms compared to bacterial epiglottitis. - It is a **bacterium lacking a cell wall** and does not typically cause the acute, life-threatening inflammation characteristic of epiglottitis.

Question 2244: Residual auditory defect is a common complication in meningitis caused by

A. Staphylococcus
B. Meningococcus
C. Escherichia coli
D. Haemophilus influenzae (Correct Answer)

Explanation: ***Haemophilus influenzae*** - *Haemophilus influenzae* type b (Hib) meningitis has the **highest rate of sensorineural hearing loss** among bacterial meningitis causes, affecting **5-35% of survivors**. - Direct damage to the **cochlea and auditory nerve** occurs from intense inflammation, bacterial toxins, and cell wall components (lipopolysaccharide). - The inflammatory response leads to **labyrinthitis, cochlear obliteration**, and subsequent permanent auditory impairment. - Even though Hib meningitis is now rare due to vaccination, when it occurs, **residual hearing loss remains its most common neurological sequela**. *Staphylococcus* - **Staphylococcal meningitis** is typically associated with **neurosurgical procedures, trauma, or CSF shunt infections**, not community-acquired disease. - More commonly leads to complications like **abscess formation, ventriculitis**, or **subdural empyema** rather than isolated hearing loss. - While severe meningitis of any cause can cause auditory defects, *Staphylococcus* is not primarily recognized for this specific sequela. *Meningococcus* - **Meningococcal meningitis** (*Neisseria meningitidis*) can cause hearing loss, but at a **lower rate (5-10%)** compared to H. influenzae. - Though currently more prevalent than Hib meningitis (due to vaccination programs), the **frequency of hearing loss as a complication** is lower when comparing case-to-case outcomes. - Often associated with more dramatic systemic complications like **fulminant septicemia** and **Waterhouse-Friderichsen syndrome** rather than isolated auditory defects. *Escherichia coli* - **E. coli meningitis** primarily affects **neonates and infants**, acquired during birth from maternal gastrointestinal flora. - Main complications include **hydrocephalus, cerebral abscess, developmental delays**, and **ventriculitis**. - While neurological sequelae are common (up to 50%), **residual auditory defects are not the predominant or most characteristic long-term complication** compared to H. influenzae.

Question 2245: Pseudomembranous colitis is caused by:

A. Pseudomonas
B. Cl. welchii
C. Cl. difficile (Correct Answer)
D. Cl. perfringens

Explanation: ***Clostridium difficile*** - **Pseudomembranous colitis** is a severe inflammation of the colon, most commonly caused by an overgrowth of **Clostridium difficile** bacteria in the gut. - This overgrowth often occurs after antibiotic use, which disrupts the normal gut flora, allowing **C. difficile** to produce toxins that damage the colon lining. *Pseudomonas* - **Pseudomonas aeruginosa** is a common opportunistic pathogen but is not associated with causing **pseudomembranous colitis**. - It is more commonly linked to infections such as hospital-acquired pneumonia, urinary tract infections, and wound infections. *Clostridium welchii* - **Clostridium welchii** is an older name for **Clostridium perfringens**, and it is not the causative agent of **pseudomembranous colitis**. - **Clostridium perfringens** is primarily known for causing **gas gangrene** and a type of **food poisoning**. *Clostridium perfringens* - **Clostridium perfringens** primarily causes **gas gangrene** (a severe soft tissue infection) and certain types of **food poisoning** due to its toxin production. - Unlike **Clostridium difficile**, it does not typically cause **pseudomembranous colitis** following antibiotic use.

Question 2246: Sulfur granules in pus are seen in

A. Actinomyces israelii (Correct Answer)
B. Candida albicans
C. Nocardia brasiliensis
D. Histoplasma capsulatum

Explanation: ***Actinomyces israelii*** - **Sulfur granules** are characteristic macroscopic aggregates of filamentous bacteria found in pus from infections caused by *Actinomyces israelii*. - These granules are yellow, gritty, and represent colonies of the organism embedded in a calcium phosphate matrix, indicating an **actinomycosis infection**. *Candida albicans* - *Candida albicans* is a **yeast** that typically causes infections like thrush or candidiasis, which produce creamy white plaques or a curd-like discharge, but not sulfur granules. - It is a **fungus**, not a filamentous bacterium, and its microscopic appearance involves budding yeast cells and pseudohyphae. *Nocardia brasiliensis* - *Nocardia brasiliensis* can cause **nocardiosis**, which may involve cutaneous or pulmonary infections. While it can form granules (mycetoma-like lesions), these are not typically referred to as "sulfur granules" in the same way as *Actinomyces*. - Nocardial infections often present with abscesses and draining sinuses, and its granules are usually smaller and have a different microscopic appearance than those of *Actinomyces*. *Histoplasma capsulatum* - *Histoplasma capsulatum* is a **dimorphic fungus** that causes histoplasmosis, primarily affecting the lungs. - It exists as a mold in the environment and as yeast cells within macrophages in the host; it does not form sulfur granules in pus.

Question 2247: Causative agents of "Vincent's angina"

A. Borrelia burgdorferi and Lactobacillus
B. Leptospira and Treponema pallidum
C. Borrelia recurrentis and Bacteroides
D. Borrelia vincenti and Fusobacterium nucleatum (Correct Answer)

Explanation: ***Borrelia vincenti and Fusobacterium nucleatum*** - **Vincent's angina**, also known as **acute necrotizing ulcerative gingivitis (ANUG)**, is polymicrobial and characteristically involves a synergistic infection of **spirochetes** (like *Borrelia vincenti*, now classified as *Treponema vincentii*) and **fusobacteria** (like *Fusobacterium nucleatum*). - These organisms thrive in an anaerobic environment, leading to the characteristic ulcerative and necrotic lesions of the gingiva and oral mucosa. - This synergistic infection produces the classic "fusospirochaetal" complex seen on microscopy. *Borrelia burgdorferi and Lactobacillus* - *Borrelia burgdorferi* is the causative agent of **Lyme disease**, a tick-borne illness causing systemic symptoms, not Vincent's angina. - *Lactobacillus* species are common commensal bacteria found in the oral cavity, gut, and vagina, and are not pathogenic in the context of Vincent's angina. *Leptospira and Treponema pallidum* - *Leptospira* species cause **leptospirosis**, a zoonotic disease with symptoms like fever, headache, and muscle aches, often affecting the kidneys and liver. - *Treponema pallidum* is the causative agent of **syphilis**, a sexually transmitted infection, which presents with different oral lesions (e.g., chancre, mucous patches) that are distinct from Vincent's angina. *Borrelia recurrentis and Bacteroides* - *Borrelia recurrentis* causes **relapsing fever**, characterized by recurrent episodes of fever and other systemic symptoms, transmitted by lice or ticks. - While *Bacteroides* are common anaerobic bacteria in the oral flora, they are not the primary synergistic pair specifically associated with the distinct clinical presentation of Vincent's angina, as are the spirochetes and fusobacteria.

Question 2248: A person returns to Delhi from Bangladesh after 2 days and has diarrhea. Stool examination shows RBC's in stool. The likely organism causing is ?

A. Enteropathogenic E. Coli
B. Salmonella typhi
C. Enterotoxigenic E. Coli
D. Shigella dysenteriae (Correct Answer)

Explanation: ***Shigella dysenteriae*** - This organism causes **bacillary dysentery**, characterized by fever, abdominal cramps, and frequent, small-volume stools containing **blood and mucus (RBCs)**, which fits the clinical picture of a traveler experiencing diarrhea with RBCs in stool. - The rapid onset (within 2 days of return) and the presence of **RBCs in stool** are highly suggestive of an invasive bacterial pathogen like *Shigella*. *Enteropathogenic E. Coli* - **EPEC** typically causes **watery diarrhea**, particularly in infants, by disrupting intestinal microvilli. - It does **not usually cause bloody stools** or significant red blood cells in the stool. *Salmonella typhi* - While *Salmonella typhi* causes **typhoid fever**, its initial presentation is typically with fever, headache, and constipation, followed by a **pea-soup diarrhea** in later stages, which is usually not bloody. - The rapid onset of bloody diarrhea within 2 days is less characteristic of typhoid fever, which has a longer incubation period. *Enterotoxigenic E. Coli* - **ETEC** is a common cause of **traveler's diarrhea**, but it produces toxins that lead to **watery, non-bloody diarrhea**. - The presence of **RBCs in the stool** makes ETEC an unlikely cause in this scenario.

Question 2249: All of the following cause Fournier's gangrene except:

A. Bacteroides
B. Clostridium (Correct Answer)
C. Streptococcus
D. Staphylococcus

Explanation: ***Clostridium*** - While *Clostridium* species (especially *C. perfringens*) **CAN be isolated** from Fournier's gangrene cases and contribute to gas formation and tissue necrosis, they are **less commonly identified as primary pathogens** compared to other organisms. - In the context of this question, *Clostridium* is considered the "except" option because it is **relatively less frequently implicated** in Fournier's gangrene compared to the other listed organisms, though it is NOT entirely excluded from the microbiology of this condition. - *Clostridium* species are more classically associated with **gas gangrene (clostridial myonecrosis)** in traumatic wounds and deep muscle tissue. *Bacteroides* - ***Bacteroides fragilis*** and other **anaerobic gram-negative bacilli** are among the **most commonly isolated organisms** in Fournier's gangrene. - They produce enzymes that facilitate tissue destruction and contribute significantly to the **polymicrobial synergistic necrotizing infection**. - Essential component of the typical microbial flora in perianal and genital infections. *Streptococcus* - ***Streptococcus pyogenes*** (Group A Streptococcus) and other streptococcal species are **frequently isolated** from Fournier's gangrene. - They produce toxins and enzymes causing **rapid necrotizing fasciitis** with systemic toxicity. - Major contributor to the aggressive nature and rapid progression of the infection. *Staphylococcus* - ***Staphylococcus aureus*** (including MRSA) is **commonly found** in polymicrobial Fournier's gangrene infections. - Contributes to local tissue destruction through toxin production and enzyme activity. - Often isolated from perianal and genital skin flora, facilitating its involvement in these infections.

Question 2250: Causative organism of "glanders" is:

A. Pseudomonas pseudomallei
B. Leptospira
C. Chlamydia
D. Burkholderia mallei (Correct Answer)

Explanation: ***Burkholderia mallei*** - **_Burkholderia mallei_** is the bacterial species responsible for causing **glanders**, a contagious disease primarily affecting horses, donkeys, and mules. - Humans can contract glanders through direct contact with infected animals or contaminated materials, with respiratory and cutaneous forms of the disease being common. *Pseudomonas pseudomallei* - **_Pseudomonas pseudomallei_** (`_Burkholderia pseudomallei_`) is the causative agent of **melioidosis**, a severe infection with a wide range of clinical manifestations. - While it's closely related to _Burkholderia mallei_, melioidosis is distinct from glanders and typically found in tropical and subtropical regions. *Leptospira* - **_Leptospira_** is a spirochete bacterium responsible for **leptospirosis**, a zoonotic disease that affects both animals and humans. - It is typically transmitted through contact with water or soil contaminated with the urine of infected animals, presenting with fever, headache, body aches, and sometimes severe organ damage. *Chlamydia* - **_Chlamydia_** is a genus of intracellular bacteria known for causing a variety of infections in humans, including sexually transmitted infections (STIs), eye infections (`_trachoma_`), and respiratory infections. - It is not associated with glanders, which is caused by a distinct bacterial species with a different mode of transmission and host range.

Practice by Chapter

Staphylococci

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Streptococci and Enterococci

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Neisseria and Moraxella

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Corynebacterium and Listeria

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Bacillus and Clostridium

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Enterobacteriaceae

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Vibrio, Aeromonas, and Plesiomonas

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Pseudomonas and Related Bacteria

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Haemophilus and HACEK Group

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Bordetella and Brucella

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Mycobacteria

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Spirochetes

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