Bacteriology Practice Questions

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: 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: 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: 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: Who discovered the bacterium Treponema pallidum?

Fritz Schaudinn and Erich Hoffmann. ***Fritz Schaudinn and Erich Hoffmann*** - **Fritz Schaudinn** was a German zoologist, and **Erich Hoffmann** was a German dermatologist; they jointly discovered **Treponema pallidum** in **1905**. - Their discovery of the spirochete was a crucial step in understanding the etiology of **syphilis**. *Robert Koch* - **Robert Koch** is renowned for identifying the causative agents of **tuberculosis**, **cholera**, and **anthrax**. - He developed Koch's postulates, a fundamental set of criteria for establishing the causal relationship between a microbe and a disease. *Twort* - **Frederick Twort** was a British bacteriologist who is credited with the discovery of **bacteriophages** in **1915**. - His work involved examining transparent areas in bacterial cultures, leading to the identification of lytic viruses that infect bacteria. *Ellerman* - **Vilhelm Ellerman** was a Danish pathologist known for his work in **hematology** and **virology**. - Alongside **Olaf Bang**, he demonstrated that avian leukemia (erythroleukemia) could be transmitted by a filterable agent, indicating a viral etiology for some cancers.

Q: Pseudomonas is which type of bacteria?

Aerobic. ***Aerobic*** - **Pseudomonas aeruginosa** is a classic example of an **aerobic bacterium**, meaning it requires oxygen for growth and metabolism. - Its ability to thrive in aerobic environments contributes to its prevalence in hospital settings and its capacity to cause a wide range of infections. *Anaerobic* - Anaerobic bacteria grow in the absence of oxygen and often die in its presence. **Pseudomonas** does not exhibit this characteristic. - Examples of anaerobic bacteria include *Clostridium* species. *Microaerophilic* - Microaerophilic bacteria require oxygen but only in low concentrations (5-10%), higher concentrations are inhibitory. - **Pseudomonas** grows optimally in atmospheric oxygen levels, not restricted to low concentrations. *Obligate anaerobe* - Obligate anaerobes are severely inhibited or killed by oxygen. - This is the opposite of **Pseudomonas**, which strictly requires oxygen for survival.

Q: Which of the following is called Preisz-Nocard bacillus?

C. pseudotuberculosis. ***C. pseudotuberculosis*** - This bacterium is historically known as the **Preisz-Nocard bacillus**, named after its discoverers. - It is an important pathogen in animals, causing conditions like **caseous lymphadenitis** in sheep and goats. *C. diphtheriae* - This bacterium causes **diphtheria** and is known for producing a potent **exotoxin** that can lead to systemic complications. - It forms a characteristic **pseudomembrane** in the throat and is not associated with the Preisz-Nocard designation. *M. tuberculosis* - This is the causative agent of **tuberculosis** in humans, primarily affecting the lungs. - It is known for its **acid-fast staining** property and a complex pathogenesis involving granuloma formation. *Mycoplasma* - This genus includes bacteria that lack a **cell wall**, making them resistant to many common antibiotics. - They are known for causing various infections, including **atypical pneumonia** and genitourinary tract infections, but are not referred to as the Preisz-Nocard bacillus.

Q: Boutonneuse fever is caused by which of the following?

B. Rickettsia conorii. ***Rickettsia conorii*** - **Boutonneuse fever**, also known as Mediterranean spotted fever, is specifically caused by the bacterium **Rickettsia conorii**. - This zoonotic disease is transmitted to humans through the bite of infected ticks, primarily the **dog tick** (Rhipicephalus sanguineus). *Rickettsia japonica* - **Rickettsia japonica** is the causative agent of **oriental spotted fever**, a tick-borne illness primarily found in Japan. - This Rickettsial disease is distinct from Boutonneuse fever, having a different geographical distribution and primary vector. *Rickettsia sibirica* - **Rickettsia sibirica** is responsible for **Siberian tick typhus** (North Asian tick typhus), which is prevalent in Siberia, Mongolia, and Northern China. - While also a tick-borne Rickettsial infection, its clinical presentation and geographic range differ from Boutonneuse fever. *Rickettsia australis* - **Rickettsia australis** causes **Queensland tick typhus**, an indigenous Rickettsial disease found in Australia. - This pathogen is distinct from Rickettsia conorii and causes a localized form of tick typhus.

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: Which of the following is a superantigen ?

TSST. ***TSST*** - **Toxic Shock Syndrome Toxin-1 (TSST-1)** is a classic example of a superantigen produced by *Staphylococcus aureus*. - Superantigens **bind directly to MHC class II molecules and T-cell receptors (TCRs)** outside of the antigen-binding groove, leading to non-specific activation of a large percentage of T cells and a massive release of cytokines. *Cholera toxin* - **Cholera toxin** is an exotoxin produced by *Vibrio cholerae* that causes massive fluid secretion in the intestine by **activating adenylate cyclase** in enterocytes. - It functions by **ADP-ribosylating the Gs alpha subunit**, leading to constitutive activation of cyclic AMP production, but it is not a superantigen. *Diphtheria toxin* - **Diphtheria toxin**, produced by *Corynebacterium diphtheriae*, inhibits protein synthesis in eukaryotic cells by **ADP-ribosylating elongation factor-2 (EF-2)**. - This action leads to cell death and the characteristic pseudomembrane formation in diphtheria, but it does not act as a superantigen. *Vero-cytoxin* - **Vero-cytoxin** (also known as Shiga toxin or Shiga-like toxin) is produced by *E. coli* O157:H7 and other Shiga toxin-producing *E. coli* (STEC). - It inhibits protein synthesis by **cleaving ribosomal RNA**, primarily causing damage to intestinal cells and renal endothelial cells, but it is not a superantigen.

Question 1

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 2

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 3

Empyema thoracis is most commonly caused by which organism

Accepted Answer

Streptococcus pneumoniae

Answer

Pseudomonas

Answer

Staphylococcus aureus

Answer

Mycobacterium

Question 4

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 5

Who discovered the bacterium Treponema pallidum?

Accepted Answer

Fritz Schaudinn and Erich Hoffmann

Answer

Robert Koch

Answer

Twort

Answer

Ellerman

Question 6

Pseudomonas is which type of bacteria?

Accepted Answer

Aerobic

Answer

Anaerobic

Answer

Microaerophilic

Answer

Obligate anaerobe

Question 7

Which of the following is called Preisz-Nocard bacillus?

Accepted Answer

C. pseudotuberculosis

Answer

C. diphtheriae

Answer

M. tuberculosis

Answer

Mycoplasma

Question 8

Boutonneuse fever is caused by which of the following?

Accepted Answer

B. Rickettsia conorii

Answer

A. Rickettsia japonica

Answer

C. Rickettsia sibirica

Answer

D. Rickettsia australis

Question 9

Color of granules in mycetoma caused by Actinomadura pelletierrii -

Accepted Answer

Red

Answer

Black

Answer

Yellow

Answer

Brown

Question 10

Which of the following is a superantigen ?

Accepted Answer

TSST

Answer

Cholera toxin

Answer

Diphtheria toxin

Answer

Vero-cytoxin

Bacteriology — MCQs

Bacteriology — MCQs

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