NEET-PG 2013 - Microbiology Practice Questions

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: 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 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: The difference between contamination and infection is that in infection

Infectious agent is in the body of human. ***Infectious agent is in the body of human*** - **Infection** implies that microorganisms have successfully **invaded the host tissues** and are replicating within the body, potentially causing a host response or disease. - The presence of the pathogen *inside* the body, beyond just surface adherence, is the defining characteristic of infection. *Arthropods on the body surface* - This describes an **infestation** (e.g., lice, mites), where the arthropods are physically present on the body surface but may not have *invaded* tissues in the same way bacteria or viruses do during an infection. - While some arthropods can transmit infectious agents, their mere presence on the surface is not synonymous with an internal infection. *Infectious agent is on body surface or on non-human objects* - This scenario describes **contamination**, where microorganisms are present on surfaces (either human skin or inanimate objects) but have not yet penetrated or established themselves within host tissues. - Contamination is a potential precursor to infection but is not an infection itself. *Infectious agents on clothes* - This is a clear example of **fomite contamination**, where infectious agents are present on inanimate objects like clothing. - The microorganisms are external to the body and are not causing an infection in the person wearing the clothes unless they are transferred and subsequently invade the host.

Question 1

Pseudomonas is which type of bacteria?

Accepted Answer

Aerobic

Answer

Anaerobic

Answer

Microaerophilic

Answer

Obligate anaerobe

Question 2

Empyema thoracis is most commonly caused by which organism

Accepted Answer

Streptococcus pneumoniae

Answer

Pseudomonas

Answer

Staphylococcus aureus

Answer

Mycobacterium

Question 3

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 4

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 5

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 6

The difference between contamination and infection is that in infection

Accepted Answer

Infectious agent is in the body of human

Answer

Infectious agent is on body surface (arthropods)

Answer

Infectious agent is on body surface or on non-human objects

Answer

Infectious agent is on clothes

NEET-PG 2013 — Microbiology