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: 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: 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: 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: 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: 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 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: 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: Which of the following bacteria does not exhibit bipolar staining?

Haemophilus influenzae. ***Haemophilus influenzae*** - *Haemophilus influenzae* is a **pleomorphic coccobacillus** that typically stains uniformly and does not exhibit characteristic **bipolar staining**. - Its presence is often identified by Gram stain showing small, Gram-negative rods, but without the distinctive safety pin appearance. *Calymmatobacterium granulomatis* - *Calymmatobacterium granulomatis* (now *Klebsiella granulomatis*) is known to exhibit **bipolar staining**, often described as a **"safety pin" appearance**, especially in tissue smears from granuloma inguinale lesions. - This characteristic staining is due to the concentration of stain at the ends of the rod-shaped bacteria. *Yersinia pestis* - *Yersinia pestis*, the causative agent of plague, is classically described as having **bipolar staining**, giving it a distinctive **"safety pin" appearance** under a microscope. - This finding is a key diagnostic feature, particularly when observed in Gram-stained smears of clinical samples. *Francisella tularensis* - *Francisella tularensis* is a small, Gram-negative coccobacillus that is known to exhibit **bipolar staining**, though it may be less prominent than in *Yersinia pestis*. - This characteristic can assist in the microscopic identification of the bacterium, which causes tularemia.

Q: Which of the following Chlamydia species is primarily associated with respiratory infections?

C pneumoniae. ***C pneumoniae*** - *C. pneumoniae* is the **primary Chlamydia species** associated with **respiratory infections** in humans - It is a common cause of **community-acquired pneumonia** (5-10% of cases), **atypical pneumonia**, **bronchitis**, **pharyngitis**, and **sinusitis** - Transmission occurs via **respiratory droplets** from person to person - Causes both **acute and chronic respiratory infections** and has been linked to exacerbations of asthma and COPD - It is the most frequently encountered Chlamydia species in respiratory tract infections *C psittaci* - Causes **psittacosis** (ornithosis), a specific type of **atypical pneumonia** transmitted from **birds** (parrots, pigeons, poultry) - While it does cause respiratory infection, it is much **less common** than C. pneumoniae and is associated with **occupational or recreational bird exposure** - Not the primary Chlamydia species for general respiratory infections *C trachomatis* - Primarily causes **genital tract infections** (urethritis, cervicitis, PID) and **ocular infections** (trachoma, inclusion conjunctivitis) - Can cause **neonatal pneumonia** in infants exposed during birth, presenting at 1-3 months of age with a staccato cough - NOT a primary respiratory pathogen in adults *None of the options* - This is incorrect because **C. pneumoniae** is definitively the Chlamydia species primarily associated with respiratory infections

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

Which organism causes puerperal sepsis?

Accepted Answer

Group A beta hemolytic streptococci

Answer

CMV

Answer

Toxoplasma gondii

Answer

Group B beta hemolytic streptococci

Question 3

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 4

Empyema thoracis is most commonly caused by which organism

Accepted Answer

Streptococcus pneumoniae

Answer

Pseudomonas

Answer

Staphylococcus aureus

Answer

Mycobacterium

Question 5

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 6

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 7

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 8

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 9

Which of the following bacteria does not exhibit bipolar staining?

Accepted Answer

Haemophilus influenzae

Answer

Yersinia pestis

Answer

Calymmatobacterium granulomatis

Answer

Francisella tularensis

Question 10

Which of the following Chlamydia species is primarily associated with respiratory infections?

Accepted Answer

C pneumoniae

Answer

C psittaci

Answer

C trachomatis

Answer

None of the options

Bacteriology — MCQs

Bacteriology — MCQs

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