Bacteriology — MCQs

A 16-year-old girl presents with a painfully enlarged lymph node in her right axilla and low grade fever. Peripheral blood counts are within normal limits. The lymph node is biopsied, and numerous granulomas filled with neutrophils and necrotic debris are observed. Which of the following organisms could produce this disease?

Q2219

The following is the etiological agent of Rocky Mountain spotted fever:

Q2220

Which is the most common organism causing acute epiglottitis among the following options?

Bacteriology Indian Medical PG Practice Questions and MCQs

Question 2211: Gas gangrene can be caused by all Except

A. Clostridium sporogenes
B. Clostridium difficile (Correct Answer)
C. Clostridium septicum
D. Clostridium bifermentans

Explanation: ***Clostridium difficile*** - *Clostridium difficile* is primarily known for causing **pseudomembranous colitis** and **antibiotic-associated diarrhea**, not gas gangrene. - Its pathogenic mechanisms involve **toxins A and B** which cause colonic inflammation and damage, distinct from the tissue destruction and gas production seen in gas gangrene. *Clostridium sporogenes* - *Clostridium sporogenes* is an anaerobic bacterium that can produce **gas** and contribute to **tissue necrosis** in mixed infections, including gas gangrene. - While not one of the most common causes, it possesses enzymatic capabilities that can degrade tissues and support the anaerobic environment characteristic of gas gangrene. *Clostridium septicum* - *Clostridium septicum* is a significant cause of **spontaneous gas gangrene**, especially in patients with **hematological malignancies** or **colonic pathologies**. - It is highly invasive and can rapidly spread through tissues, producing potent toxins that lead to extensive myonecrosis and gas formation. *Clostridium bifermentans* - *Clostridium bifermentans* is one of the less common species of *Clostridium* that can cause **gas gangrene**, particularly in **polymicrobial infections**. - It is capable of producing **proteolytic enzymes** that contribute to tissue destruction and the characteristic foul-smelling discharge associated with clostridial myonecrosis.

Question 2212: Which of the following is not a biovar of Corynebacterium diphtheriae?

A. Belfanti
B. Meningitidis (Correct Answer)
C. Gravis
D. Intermedius

Explanation: ***Meningitidis*** - **Meningitidis** is the species name for *Neisseria meningitidis*, a bacterium known for causing **meningitis** and other invasive diseases. - It is **not a biovar** or strain type of *Corynebacterium diphtheriae*, the causative agent of diphtheria. *Belfanti* - **Belfanti** is one of the recognized **biovars of *Corynebacterium diphtheriae***, known for its biochemical characteristics differentiating it from other strains. - While it can cause diphtheria, it is generally associated with milder symptoms compared to other biovars. *Gravis* - **Gravis** is a clinically significant **biovar of *Corynebacterium diphtheriae***, historically associated with severe forms of diphtheria. - It is known for its ability to produce potent toxins and cause widespread outbreaks. *Intermedius* - **Intermedius** is another established **biovar of *Corynebacterium diphtheriae***, exhibiting biochemical traits that differentiate it from Gravis and Mitis. - It is also capable of causing diphtheria, although its clinical presentation can vary.

Question 2213: The term 'leathery' appearance in medical terminology is characteristically used to describe:

A. Anthrax
B. Neisseria
C. Diphtheria (Correct Answer)
D. Proteus

Explanation: ***Diphtheria*** - The term "leather" in medical terminology is commonly used to describe the **pseudomembrane** found in diphtheria, which is tough, leathery, and firmly adherent. - This **pseudomembrane** is composed of fibrin, bacteria, inflammatory cells, and necrotic tissue, and its removal can cause bleeding. *Anthrax* - Anthrax typically causes a **black eschar** with surrounding edema, which is distinct from the leathery pseudomembrane of diphtheria. - The characteristic lesion is often referred to as a **malignant pustule** and is not described as "leather." *Neisseria* - Infections caused by *Neisseria* species, such as **meningitis** or **gonorrhea**, do not involve the formation of a leathery pseudomembrane. - *Neisseria meningitidis* can cause **purpuric rash** and petechiae, while *Neisseria gonorrhoeae* typically causes mucopurulent discharges. *Proteus* - *Proteus* species are common causes of **urinary tract infections** and wound infections. - These infections do not produce a "leathery" appearance or pseudomembrane and are known for their strong **ammonia-like odor** in urine.

Question 2214: In a patient of the nephrotic syndrome with spontaneous bacterial peritonitis, which one of the following micro-organisms is most commonly involved?

A. Proteus
B. Pneumococcus (Correct Answer)
C. Escherichia
D. Staphylococcus

Explanation: ***Pneumococcus*** - **Streptococcus pneumoniae (Pneumococcus)** is the **most common** causative organism of **spontaneous bacterial peritonitis (SBP)** in patients with **nephrotic syndrome**, especially in children. - Nephrotic syndrome causes loss of **immunoglobulins (IgG)** in the urine, leading to **opsonization defects** that increase susceptibility to **encapsulated organisms** like Pneumococcus. - The organism typically reaches the peritoneal cavity via **hematogenous spread** from respiratory or other primary sites. - This contrasts with SBP in **cirrhotic ascites**, where gram-negative enteric organisms predominate. *Escherichia* - **Escherichia coli (E. coli)** is the most common cause of SBP in **cirrhotic patients** with ascites (due to bacterial translocation from the gut). - In **nephrotic syndrome**, E. coli is a less common cause compared to Pneumococcus, as the immune defect specifically affects defense against encapsulated organisms. - The pathophysiology differs between cirrhosis (portal hypertension, bacterial translocation) and nephrotic syndrome (immunoglobulin loss). *Proteus* - **Proteus mirabilis** is an uncommon cause of spontaneous bacterial peritonitis in nephrotic syndrome. - Proteus is more frequently associated with **urinary tract infections**, especially in patients with structural abnormalities or catheterization. *Staphylococcus* - **Staphylococcus** species are rare causes of primary spontaneous bacterial peritonitis in nephrotic syndrome. - When present, Staphylococcus usually suggests **secondary peritonitis** from perforation, surgical complications, or catheter-related peritonitis (e.g., peritoneal dialysis).

Question 2215: All of the following statements about cholera are true except -

A. Culture medium is TCBS Agar
B. O & H antigens measure carrier state (Correct Answer)
C. Produces indole and reduces nitrate
D. Synthesize neuraminidase

Explanation: ***O & H antigens measure carrier state*** - **O and H antigens** are primarily involved in serotyping *Vibrio cholerae* and are crucial for the initial classification of different strains, particularly differentiating between toxigenic and non-toxigenic strains. - The detection of **carrier states** in cholera is typically achieved through culturing stool samples for the presence of *Vibrio cholerae*, rather than by measuring O and H antigens, as these antigens reflect the bacterial surface components. *Culture medium is TCBS Agar* - **Thiosulfate-citrate-bile salts-sucrose (TCBS) agar** is a selective and differential medium widely used for isolating *Vibrio* species, including *Vibrio cholerae*, from clinical samples and environmental sources. - It works by inhibiting the growth of most enteric bacteria while allowing *Vibrio* species to grow and produce distinct colonies (e.g., yellow colonies for sucrose-fermenting *V. cholerae*). *Produces indole and reduces nitrate* - *Vibrio cholerae* is biochemically characterized by its ability to **produce indole** from tryptophan and to **reduce nitrates** to nitrites, which are important diagnostic markers. - These metabolic activities are part of the standard battery of biochemical tests used to identify and confirm the presence of *Vibrio cholerae* in laboratory settings. *Synthesize neuraminidase* - *Vibrio cholerae* produces **neuraminidase**, an enzyme that cleaves **sialic acid** residues from mucin, potentially enhancing the binding of cholera toxin to intestinal epithelial cells by exposing GM1 ganglioside receptors. - This enzyme contributes to the pathogen's virulence by modifying the host's intestinal environment, although its direct role in disease pathogenesis is still under investigation.

Question 2216: “Hundred day cough” is the name of

A. Cough due to Haemophilus influenzae
B. Cough due to respiratory syncytial virus
C. Cough due to Bordetella pertussis (Correct Answer)
D. Cough due to adenovirus

Explanation: ***Cough due to Bordetella pertussis*** - **Whooping cough**, caused by **Bordetella pertussis**, is colloquially known as the "hundred-day cough" due to its prolonged duration. - The cough can last for weeks to months, especially in unvaccinated individuals, characterized by severe paroxysms followed by a characteristic "whoop" inspiration. *Cough due to Haemophilus influenzae* - **Haemophilus influenzae** can cause respiratory infections like bronchitis or pneumonia, with cough as a symptom, but it is not specifically known as the "hundred-day cough." - This bacterium is more commonly associated with **otitis media**, sinusitis, epiglottitis, and meningitis, rather than a prolonged, distinctive coughing illness. *Cough due to respiratory syncytial virus* - **Respiratory syncytial virus (RSV)** is a common cause of respiratory infections, particularly in infants and young children, leading to bronchiolitis and pneumonia. - While RSV can cause a persistent cough, it is not referred to as the "hundred-day cough"; its symptoms are typically more acute and can involve wheezing and difficulty breathing. *Cough due to adenovirus* - **Adenoviruses** can cause various respiratory illnesses ranging from the common cold to pneumonia, with cough being a frequent symptom. - However, the cough associated with adenovirus infections is generally not as prolonged or severe as "whooping cough" and does not typically fit the "hundred-day cough" description.

Question 2217: Scrub typhus is caused by:

A. R.akari
B. R.typhi
C. Orientia tsutsugamushi (Correct Answer)
D. R.conorii

Explanation: ***R.tsutsugamushi*** - **Scrub typhus** is specifically caused by **Orientia tsutsugamushi**, which was formerly classified as *Rickettsia tsutsugamushi*. - This organism is transmitted by the bite of infected **chiggers** (larval mites) found in certain geographical areas. *R.akari* - *Rickettsia akari* is the causative agent of **rickettsialpox**, a mild rickettsial disease characterized by an eschar and a vesicular rash. - It is transmitted by the bite of an infected **mite**, specifically the house mouse mite, *Liponyssoides sanguineus*. *R.typhi* - *Rickettsia typhi* is responsible for **murine typhus** (also known as endemic typhus), a rickettsial disease. - This bacterium is transmitted to humans by the bite of an infected **flea**, typically the rat flea (*Xenopsylla cheopis*). *R. conorii* - *Rickettsia conorii* causes **Mediterranean spotted fever**, also known as boutonneuse fever or Israeli spotted fever. - It is transmitted by the bite of infected **ticks**, primarily the dog tick (*Rhipicephalus sanguineus*).

Question 2218: A 16-year-old girl presents with a painfully enlarged lymph node in her right axilla and low grade fever. Peripheral blood counts are within normal limits. The lymph node is biopsied, and numerous granulomas filled with neutrophils and necrotic debris are observed. Which of the following organisms could produce this disease?

A. Bartonella henselae (Correct Answer)
B. Chlamydia psittaci
C. Coxiella burnetii
D. Borrelia burgdorferi

Explanation: ***Bartonella henselae*** - This organism causes **cat scratch disease (CSD)**, which typically presents with **lymphadenopathy** (often in the axilla) following a cat scratch or bite. - The characteristic histological finding in CSD is **suppurative granulomas** (granulomas with central necrosis and neutrophils), or **stellate microabscesses**, in the affected lymph nodes. *Chlamydia psittaci* - This bacterium causes **psittacosis**, primarily a respiratory illness (pneumonia) acquired from birds. - While it can cause systemic symptoms like **fever**, it is not typically associated with localized, painful suppurative lymphadenopathy or granulomas in the axilla. *Coxiella burnetii* - This organism is the causative agent of **Q fever**, which can present as an acute febrile illness, pneumonia, or hepatitis, often from exposure to infected farm animals. - It does not typically cause localized painful lymphadenopathy with suppurative granulomas in the axilla. *Borrelia burgdorferi* - This bacterium causes **Lyme disease**, characterized by an expanding erythematous rash (erythema migrans), followed by joint, cardiac, and neurological manifestations. - Primary findings do not include suppurative granulomas in lymph nodes, although general lymphadenopathy can occur.

Question 2219: The following is the etiological agent of Rocky Mountain spotted fever:

A. Coxiella burnetii
B. Rochalimaea quintana
C. Rickettsia rickettsii (Correct Answer)
D. Rickettsia tsutsugamushi

Explanation: ***Rickettsia rickettsii*** - This bacterium is the definitive **causative agent** of **Rocky Mountain spotted fever (RMSF)**. - RMSF is a severe **tick-borne disease** endemic to the Americas, characterized by fever, headache, and a distinctive rash. *Coxiella burnetii* - This bacterium causes **Q fever**, an acute or chronic infectious disease often presenting with flu-like symptoms or pneumonia. - Unlike *Rickettsia rickettsii*, it is **not transmitted by ticks** in the same way and does not cause a spotted rash. *Rochalimaea quintana* - Now known as **Bartonella quintana**, this bacterium is the etiologic agent of **trench fever** and can cause chronic bacteremia in individuals experiencing homelessness. - It is primarily transmitted by **body lice** and does not cause RMSF. *Rickettsia tsutsugamushi* - This bacterium is the causative agent of **scrub typhus**, a common febrile illness in Asia and the Pacific. - **Scrub typhus** is transmitted by infected chiggers and is characterized by a distinctive eschar, which is not typical for RMSF.

Question 2220: Which is the most common organism causing acute epiglottitis among the following options?

A. N. Meningitidis
B. H. influenzae (Correct Answer)
C. S. pyogenes
D. S. Pneumoniae

Explanation: ***H. influenzae*** - **_Haemophilus influenzae_ type b (Hib)** was historically the **most common cause** of acute epiglottitis, particularly in children before widespread Hib vaccination. - This remains the **classically taught answer** in medical education and is still relevant in **unvaccinated populations** or areas with low vaccination coverage. - **Important note:** In the **post-vaccine era** with widespread Hib vaccination, the incidence has decreased by >95%, and other organisms (particularly _Streptococcus_ species) have become relatively more common, especially in adults. - However, H. influenzae remains the organism most associated with acute epiglottitis in traditional medical teaching. *N. meningitidis* - **_Neisseria meningitidis_** primarily causes **meningococcal meningitis** and **meningococcemia** (fulminant septicemia). - While it can cause various invasive infections, it is **not a common cause** of acute epiglottitis. - Characteristic features include petechial/purpuric rash in septicemia. *S. pyogenes* - **_Streptococcus pyogenes_** (Group A Streptococcus) is the leading cause of **acute bacterial pharyngitis** ("strep throat"). - It causes complications like **acute rheumatic fever** and **acute post-streptococcal glomerulonephritis**. - In the post-Hib vaccine era, it has emerged as an **increasingly common cause** of epiglottitis, especially in adults, but is still less classically associated than H. influenzae in traditional teaching. *S. pneumoniae* - **_Streptococcus pneumoniae_** is a major cause of **community-acquired pneumonia, acute otitis media, bacterial meningitis**, and **bacteremia**. - While it can cause **supraglottitis/epiglottitis** (particularly in adults in the modern era), it is **less classically associated** with acute epiglottitis compared to the traditional pathogen H. influenzae type b.

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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