Bacteriology Practice Questions

Q: "Citron bodies" are boat- or leaf-shaped pleomorphic organisms found in exudates. This is a characteristic feature of which organism?

Cl. septicum. ***Cl. septicum*** - *Clostridium septicum* characteristically forms **"Citron bodies"** - boat-shaped or leaf-shaped pleomorphic organisms in exudates - These spindle-shaped, cigar-like forms are a **distinctive morphological feature** of this organism - Associated with **gas gangrene** and spontaneous myonecrosis, particularly in patients with underlying malignancy or neutropenia - The pleomorphic morphology distinguishes it from other clostridial species *Cl. welchii* - *Clostridium perfringens* (formerly *Cl. welchii*) appears as **large, rectangular, "boxcar-shaped" Gram-positive rods** - Does **not** form citron bodies or show the characteristic boat/leaf-shaped pleomorphism - Most common cause of gas gangrene but has different morphological appearance *Cl. edematiens* - *Clostridium oedematiens* (now *Clostridium novyi*) appears as **large, Gram-positive rods** with subterminal spores - Does not form citron bodies - Associated with gas gangrene but lacks the pleomorphic morphology described *Cl. tetani* - *Clostridium tetani* has characteristic **terminal spores** giving a "drumstick" or "tennis racket" appearance - Does not form citron bodies or pleomorphic shapes - Morphologically distinct with its terminal spore appearance

Q: A patient presents with purulent urethral discharge and laboratory findings of gram-negative diplococci on modified Thayer-Martin media. What is the most likely diagnosis?

Neisseria gonorrhoeae. ***Neisseria gonorrhoeae*** - **Purulent urethral discharge** and identification of **gram-negative diplococci** on microscopy from a urethral swab are highly characteristic of *Neisseria gonorrhoeae* infection. - *N. gonorrhoeae* grows well on **modified Thayer-Martin media**, a selective medium specifically designed for *Neisseria* species. - This organism is the causative agent of **gonorrhea**, a common sexually transmitted infection. - The combination of clinical presentation (purulent discharge) and laboratory findings (gram-negative diplococci on Thayer-Martin media) makes this the definitive diagnosis. *Haemophilus ducreyi* - Causes **chancroid**, which presents with **painful genital ulcers** and **lymphadenopathy**, NOT purulent urethral discharge. - *H. ducreyi* is a gram-negative **bacillus** (rod-shaped), NOT diplococci. - It requires special media supplemented with X and V factors for growth, not primarily Thayer-Martin medium. *Treponema pallidum* - Causes **syphilis**, which typically presents with a **chancre** (painless ulcer) in primary stage and systemic symptoms in later stages. - Cannot be cultured on routine media and is identified by **darkfield microscopy** or serological tests. - Does not appear as gram-negative diplococci. *Chlamydia trachomatis* - Can cause urethritis with **mucopurulent or watery discharge**, but not typically purulent. - *Chlamydia* are **obligate intracellular bacteria** that cannot be visualized as gram-negative diplococci on gram stain. - Cannot be cultured on standard bacteriologic media like Thayer-Martin medium.

Q: Which organism causes puerperal sepsis?

Group A beta hemolytic streptococci. ***Group A beta hemolytic streptococci*** - **Group A Streptococcus (GAS)**, specifically *Streptococcus pyogenes*, is the **classic and most important cause of puerperal sepsis** (puerperal fever). - Historically, GAS was responsible for devastating epidemics of puerperal fever in maternity wards before the introduction of antiseptic practices by Ignaz Semmelweis. - GAS causes severe, rapidly progressive postpartum infections with **high morbidity and mortality** if untreated. - Clinically presents with fever, severe uterine tenderness, and can progress to **toxic shock syndrome** and septicemia. *Group B beta hemolytic streptococci* - **Group B Streptococcus (GBS)**, *Streptococcus agalactiae*, can cause postpartum endometritis and maternal infections. - However, GBS is **more commonly associated with neonatal sepsis** rather than being the primary cause of classic puerperal sepsis. - While it can colonize the genital tract and cause infection, it is not the historical or most severe cause of puerperal fever. *CMV* - **Cytomegalovirus (CMV)** is a viral infection that causes congenital infections when transmitted in utero. - It is not a bacterial cause of **puerperal sepsis**, which is primarily a bacterial postpartum infection. *Toxoplasma gondii* - **Toxoplasma gondii** is a parasite causing toxoplasmosis, which can lead to congenital abnormalities. - It is not associated with **puerperal sepsis**, which is a bacterial infection of the postpartum period.

Q: Empyema thoracis is most commonly caused by which organism

Streptococcus pneumoniae. ***Streptococcus pneumoniae*** - This is the **most common cause of empyema thoracis**, accounting for **40-70% of all cases** in most published series - It is the leading cause of **community-acquired pneumonia** that progresses to parapneumonic effusion and empyema - The pneumococcal infection leads to **inflammatory exudation** into the pleural space, which can progress through exudative, fibrinopurulent, and organizing phases to form frank empyema - Remains the most frequent causative organism across all age groups in community-acquired empyema *Staphylococcus aureus* - An important but **less common cause** of empyema, accounting for approximately 10-20% of cases - More frequently seen in **specific clinical contexts**: post-influenza pneumonia, hospital-acquired infections, hematogenous spread, and pediatric empyema - Causes **severe, necrotizing infections** with abscess formation and is associated with higher morbidity - While clinically significant, it is **not the most common** overall cause *Pseudomonas* - *Pseudomonas aeruginosa* is primarily associated with **nosocomial empyema** in hospitalized patients - Risk factors include **ventilator-associated pneumonia**, immunosuppression, and **cystic fibrosis** - Accounts for a small percentage of empyema cases overall *Mycobacterium* - *Mycobacterium tuberculosis* causes **tuberculous empyema**, a chronic condition with characteristic **thick pleural fluid** and caseous material - Important in regions with high TB prevalence but represents a distinct entity from acute bacterial empyema - Not a common cause of acute pyogenic empyema in most settings

Q: An adult male presents with chronic atrophic gastritis. Growth on Skirrow's medium and a positive rapid urease test were observed. What is the most likely diagnosis?

H. pylori. ***H pylori*** - The combination of **chronic atrophic gastritis**, growth on **Skirrow's medium**, and a **positive rapid urease test** is highly characteristic of *Helicobacter pylori* infection. - *H. pylori* is a known cause of **gastritis**, peptic ulcers, and is the only bacterium that produces large amounts of **urease**, which is detected by the rapid urease test. *H. influenzae* - This bacterium is primarily associated with **respiratory tract infections**, meningitis, and otitis media, not gastric conditions. - It does not typically grow on Skirrow's medium and is not known to produce significant urease for a positive rapid urease test. *K. pneumoniae* - *Klebsiella pneumoniae* is a common cause of **pneumonia**, urinary tract infections, and sepsis, with no direct involvement in chronic atrophic gastritis or urease production in the stomach. - It does not typically grow on selective media like Skirrow's, which is designed for microaerophilic organisms. *V. cholerae* - *Vibrio cholerae* is the causative agent of **cholera**, characterized by severe watery diarrhea, and is not associated with gastric inflammation or positive urease tests in this context. - It grows on specific media like TCBS agar and does not cause chronic atrophic gastritis.

Q: What is the most common cause of a peritonsillar abscess?

Group A beta-hemolytic streptococcus. ***Group A beta-hemolytic streptococcus*** - This bacterium, also known as **_Streptococcus pyogenes_**, is the most common cause of **streptococcal pharyngitis**, which is the precursor to most peritonsillar abscesses. - Peritonsillar abscesses are typically a complication of untreated or inadequately treated **tonsillitis**. *Streptococcus pneumoniae* - While **_Streptococcus pneumoniae_** can cause upper respiratory infections like sinusitis and otitis media, it is not the primary cause of peritonsillar abscesses. - Its infections are more commonly associated with **pneumonia** and **meningitis**. *Staphylococcus aureus* - **_Staphylococcus aureus_** is a common cause of skin and soft tissue infections, but it is less frequently isolated as the primary pathogen in peritonsillar abscesses. - It can be involved in **polymicrobial infections** or as a secondary invader. *H. influenzae* - **_Haemophilus influenzae_** can cause various infections, particularly in children, such as otitis media and epiglottitis. - However, it is not considered the most common cause of **peritonsillar abscesses**.

Q: The most common cause of meningitis in children aged 5 yrs is-

S. pneumoniae. ***S. pneumoniae*** - **_Streptococcus pneumoniae_** (Pneumococcus) is the **most common cause of bacterial meningitis** in children aged 5 years and older, as well as in adults. - Widespread vaccination has reduced its incidence but it remains a significant pathogen. *H. influenzae* - **_Haemophilus influenzae_ type b (Hib)** was a major cause of meningitis in young children, but its incidence has **drastically decreased** due to the routine **Hib vaccine**. - Without vaccination, it would still be a significant cause in this age group, but with high vaccine coverage, it is less common than _S. pneumoniae_. *Staphylococcus* - **_Staphylococcus aureus_** and other staphylococcal species are **less common causes of meningitis** in otherwise healthy children. - They are more typically associated with meningitis following **neurosurgery**, trauma, or in immunocompromised patients. *E.coli* - **_Escherichia coli_** is a common cause of **neonatal meningitis** (in infants less than 3 months old), often acquired during passage through the birth canal. - It is **rarely a cause of meningitis** in children aged 5 years.

Q: What is the most common cause of acute tonsillitis?

Group A beta-hemolytic streptococci. ***Group A beta-hemolytic streptococci*** - **Group A Streptococcus (GAS)**, specifically *Streptococcus pyogenes*, is the most frequent bacterial cause of **acute tonsillitis** and pharyngitis, especially in school-aged children. - Infection can lead to complications such as **rheumatic fever** and **post-streptococcal glomerulonephritis** if not appropriately treated. *Streptococcus pneumoniae* - While *S. pneumoniae* is a common cause of **otitis media**, **sinusitis**, and **pneumonia**, it is less commonly the primary cause of acute tonsillitis. - It typically causes respiratory infections involving the lower airways or adjacent structures rather than primarily tonsillar inflammation. *H. Influenza* - *Haemophilus influenzae* is a significant pathogen for **otitis media**, **epiglottitis**, and **meningitis**, particularly in unvaccinated children. - It is not a common primary cause of acute tonsillitis, which is predominantly bacterial or viral. *Staphylococcus aureus* - *Staphylococcus aureus* is often associated with **skin and soft tissue infections**, as well as more serious conditions like **sepsis** and **endocarditis**. - Although it can cause pharyngeal infections, it is an infrequent cause of acute tonsillitis compared to Group A Streptococcus.

Q: Color of granules in mycetoma caused by Actinomadura pelletierrii -

Red. ***Red*** - *Actinomadura pelletierrii* is a common cause of **actinomycetoma** and is characterized by producing **red granules** in the lesions. - The color of these granules is a key diagnostic feature, helping differentiate it from other causes of mycetoma. *Black* - **Black granules** are typically associated with **eumycetoma** caused by **dematiaceous fungi** such as *Madurella mycetomatis*. - This color indicates the presence of **melanin**, a pigment produced by these fungal species. *Yellow* - **Yellow granules** are commonly seen in actinomycetoma caused by organisms such as *Nocardia brasiliensis* or sometimes *Actinomadura madurae*. - This color helps differentiate these specific actinomycetes from other types that produce different granule colors. *Brown* - While varying shades of color can occur, **brown granules** are not the characteristic color produced by *Actinomadura pelletierrii*. - Some *Streptomyces* species or certain eumycetoma agents can occasionally produce brownish granules, but red is specific for *A. pelletierrii*.

Q: All are non-sporing anaerobes of medical importance except which of the following?

Clostridia. ***Clostridia*** - This genus is characterized by its ability to form **spores**, which are highly resistant structures allowing survival in adverse conditions. - Examples include *Clostridium difficile*, *Clostridium tetani*, and *Clostridium botulinum*, all of which are important human pathogens. *Actinomyces* - *Actinomyces* are **non-sporing, Gram-positive, anaerobic rods** that cause chronic, granulomatous infections, often forming sinus tracts. - They are known for producing characteristic **"sulfur granules"** in pus. *Bacteroides* - *Bacteroides* are **non-sporing, Gram-negative, anaerobic rods** that are a major component of the normal human gut flora. - They are frequently involved in **intra-abdominal infections** and abscess formation. *Fusobacterium* - *Fusobacterium* species are **non-sporing, Gram-negative, fusiform-shaped anaerobic rods**. - They are common in the **oral cavity** and can cause infections such as Vincent's angina and Lemierre's syndrome.

Question 1

"Citron bodies" are boat- or leaf-shaped pleomorphic organisms found in exudates. This is a characteristic feature of which organism?

Accepted Answer

Cl. septicum

Answer

Cl. edematiens

Answer

Cl. tetani

Answer

Cl. welchii

Question 2

A patient presents with purulent urethral discharge and laboratory findings of gram-negative diplococci on modified Thayer-Martin media. What is the most likely diagnosis?

Accepted Answer

Neisseria gonorrhoeae

Answer

Treponema pallidum

Answer

Haemophilus ducreyi

Answer

Chlamydia trachomatis

Question 3

Which organism causes puerperal sepsis?

Accepted Answer

Group A beta hemolytic streptococci

Answer

CMV

Answer

Toxoplasma gondii

Answer

Group B beta hemolytic streptococci

Question 4

Empyema thoracis is most commonly caused by which organism

Accepted Answer

Streptococcus pneumoniae

Answer

Pseudomonas

Answer

Staphylococcus aureus

Answer

Mycobacterium

Question 5

An adult male presents with chronic atrophic gastritis. Growth on Skirrow's medium and a positive rapid urease test were observed. What is the most likely diagnosis?

Accepted Answer

H. pylori

Answer

V. cholerae

Answer

H. influenzae

Answer

K. pneumoniae

Question 6

What is the most common cause of a peritonsillar abscess?

Accepted Answer

Group A beta-hemolytic streptococcus

Answer

Streptococcus pneumoniae

Answer

Staphylococcus aureus

Answer

H. influenzae

Question 7

The most common cause of meningitis in children aged 5 yrs is-

Accepted Answer

S. pneumoniae

Answer

Staphylococcus

Answer

E.coli

Answer

H. influenzae

Question 8

What is the most common cause of acute tonsillitis?

Accepted Answer

Group A beta-hemolytic streptococci

Answer

Streptococcus pneumoniae

Answer

H. influenzae

Answer

Staphylococcus aureus

Question 9

Color of granules in mycetoma caused by Actinomadura pelletierrii -

Accepted Answer

Red

Answer

Black

Answer

Yellow

Answer

Brown

Question 10

All are non-sporing anaerobes of medical importance except which of the following?

Accepted Answer

Clostridia

Answer

Bacteroides

Answer

Fusobacterium

Answer

Actinomyces

Bacteriology — MCQs

Bacteriology — MCQs

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