NEET-PG 2013 - Microbiology Practice Questions

Q: Most common organism causing ventilator associated pneumonia -

Pseudomonas. ***Pseudomonas*** - **Pseudomonas aeruginosa** is one of the most common causes of **ventilator-associated pneumonia (VAP)**, particularly in **late-onset VAP** (≥5 days) and in patients with prolonged mechanical ventilation, prior antibiotic exposure, or underlying lung disease. - Its ability to form **biofilms** and its intrinsic antibiotic resistance contribute to its prevalence in hospital-acquired infections. - Along with **Staphylococcus aureus** (especially MRSA), Pseudomonas is consistently among the leading causes of VAP in ICU settings. *Legionella* - **Legionella** is a less common cause of VAP and is typically associated with contaminated water sources, manifesting as **Legionnaires' disease**. - It usually causes severe, rapidly progressive pneumonia and is often harder to culture than other bacteria. *Pneumococcus* - **Streptococcus pneumoniae (Pneumococcus)** is the most common cause of **community-acquired pneumonia (CAP)**, but it is less frequently implicated in VAP. - While it can cause severe pneumonia and may be seen in **early-onset VAP**, its incidence in late-onset VAP is lower compared to Gram-negative rods like Pseudomonas. *Coagulase negative staphylococcus* - **Coagulase-negative Staphylococci** (e.g., *Staphylococcus epidermidis*) are common **contaminants** in cultures and primarily cause device-related infections, such as those associated with central venous catheters. - They are rarely a primary cause of VAP, as they typically have low virulence in the respiratory tract.

Q: What is the typical bacterial count in the duodenum?

10^2 per gram. ***10^2 per gram*** - The duodenum has a **relatively low bacterial count** (typically 10^2-10^4 CFU/gram) due to the **acidic environment** from gastric acid and **rapid transit** of contents. - A count of **10^2 CFU/gram** represents the **lower end of the normal range** for the proximal duodenum, where gastric acid effects are strongest. - This sparse bacterial population contrasts sharply with the dense colonization seen in the distal gut. *10^1 per gram* - This represents an **extremely low count** more characteristic of the **stomach**, not the duodenum. - Such minimal bacterial presence is due to the **hostile acidic environment** (pH 1-3) in the stomach. - The duodenum, while having low counts, consistently has higher bacterial densities than this. *10^5 per gram* - This count is characteristic of the **distal small intestine (ileum)**, where bacterial concentrations progressively increase. - A bacterial count of **10^5 per gram in the duodenum** would be considered **abnormal** and suggest **small intestinal bacterial overgrowth (SIBO)**. - SIBO occurs when colonic-type bacteria colonize the small intestine inappropriately. *10^10 per gram* - This bacterial density is typical of the **colon** (which harbors 10^11-10^12 CFU/gram), the most densely colonized part of the human gut. - Such a high count in the duodenum would indicate **severe bacterial overgrowth** or gross contamination. - The colon's anaerobic environment supports this massive bacterial population.

Q: Which is the most common bacterial organism causing bacterial upper respiratory tract infections (including sinusitis, otitis media, and pharyngitis) in adults?

Streptococcus pneumoniae. ***Streptococcus pneumoniae*** - *Streptococcus pneumoniae* is the **most common bacterial pathogen** causing upper respiratory tract infections overall, including **bacterial sinusitis**, **otitis media**, and **community-acquired pneumonia**. - It is a frequent colonizer of the nasopharynx and leads to infection when host immunity is compromised. - Accounts for the highest burden of bacterial URTIs when considering all anatomical sites. *Haemophilus influenzae* - *Haemophilus influenzae* (particularly non-typeable strains) is the **second most common** cause of bacterial sinusitis and otitis media in adults. - While significant, it is less prevalent overall than *S. pneumoniae* across all URTI types. *Staphylococcus aureus* - *Staphylococcus aureus* primarily causes **skin and soft tissue infections** and device-related infections. - It is **not a common primary pathogen** in typical acute bacterial URTIs, though it may cause secondary infections or colonize the anterior nares. *Streptococcus pyogenes* - *Streptococcus pyogenes* (Group A Streptococcus) is the **most common cause of bacterial pharyngitis** (strep throat) in adults. - However, when considering the **full spectrum of bacterial URTIs** (pharyngitis, sinusitis, otitis media), *S. pneumoniae* has a broader overall impact and higher prevalence across multiple sites.

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: In a patient presenting with respiratory symptoms, acute angled septate hyphae are seen in which of the following fungi?

Aspergillus. ***Aspergillus*** - *Aspergillus* species are characterized by their distinctive **acute-angled (dichotomous) septate hyphae** when observed microscopically in tissue sections or clinical samples. - This morphological feature is crucial for differentiating *Aspergillus* infections, such as **aspergillosis**, from other fungal infections. *Mucor* - *Mucor* (along with *Rhizopus* and *Lichtheimia*) belongs to the Zygomycetes class, which are characterized by **broad, non-septate, ribbon-like hyphae** with irregular branching, not acute-angled septate hyphae. - These fungi are associated with **mucormycosis**, often seen in immunocompromised patients, particularly those with diabetes. *Penicillium* - *Penicillium* is a common mold known for producing penicillin and typically appears as **septate hyphae** but is more often recognized by its branching, brush-like conidiophores (penicilli) in culture rather than a distinct acute-angled septate hyphal morphology in clinical samples causing invasive disease. - While it can cause opportunistic infections, its hyphae are less commonly described as having uniquely acute angles compared to *Aspergillus*. *Candida* - *Candida* species are typically observed as **yeast cells (oval budding forms)**, often forming **pseudohyphae** (elongated yeast cells that remain attached) or true hyphae under specific conditions, but not as acute-angled septate hyphae. - *Candida* is a common cause of superficial and invasive candidiasis, and its microscopic appearance is distinct from filamentous fungi.

Q: Patient came from Nagaland and shows positive test with OXK antigen. Diagnosis is?

Scrub typhus. ***Scrub typhus*** - A **positive Weil-Felix test** for the **OXK antigen** is highly suggestive of scrub typhus, particularly if the patient is from an endemic region like Nagaland. - Scrub typhus is caused by **_Orientia tsutsugamushi_**, transmitted by **chiggers** (larval mites), often presenting with fever and an **eschar**. *Trench fever* - Caused by **_Bartonella quintana_** and transmitted by the **human body louse**. - It does not typically show a positive Weil-Felix test for the OXK antigen. *Endemic typhus* - Also known as **murine typhus**, it is caused by **_Rickettsia typhi_** and transmitted by **fleas** (e.g., rat flea). - While it causes a positive Weil-Felix test, it usually involves the **OX19 antigen**, not OXK. *Epidemic typhus* - Caused by **_Rickettsia prowazekii_** and transmitted by the **human body louse**. - It yields a positive Weil-Felix test for the **OX19 and OX2 antigens**, but typically not for OXK.

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: XDR-TB is defined as resistance to which of the following drug combinations?

Fluoroquinolones plus INH plus rifampicin plus amikacin. **Fluoroquinolones plus INH plus rifampicin plus amikacin** - **Extensively drug-resistant tuberculosis (XDR-TB)** is defined by resistance to the most effective anti-TB drugs: **isoniazid (INH)**, **rifampicin**, any **fluoroquinolone**, and at least one of the three injectable second-line drugs (**amikacin**, **kanamycin**, or **capreomycin**). - This combination signifies a substantial therapeutic challenge due to limited treatment options and a high risk of treatment failure. *INH plus rifampicin* - Resistance to **INH** and **rifampicin** defines **multidrug-resistant tuberculosis (MDR-TB)**, which is a precursor to XDR-TB but not XDR-TB itself. - While serious, MDR-TB is not as extensively resistant as XDR-TB, as it doesn't include resistance to fluoroquinolones and second-line injectables. *Fluoroquinolones plus INH plus amikacin* - This combination is incomplete for the definition of XDR-TB because it omits **rifampicin** from the core definition. - XDR-TB specifically requires resistance to both **INH** and **rifampicin** (defining MDR-TB), in addition to resistance to a fluoroquinolone and one of the injectable second-line drugs. *Fluoroquinolones plus rifampicin plus kanamycin* - This combination is also incomplete for the definition of XDR-TB as it omits **isoniazid (INH)**, which is one of the two most crucial first-line drugs that characterize MDR-TB. - XDR-TB builds upon MDR-TB's resistance to both INH and rifampicin.

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.

Question 1

Most common organism causing ventilator associated pneumonia -

Accepted Answer

Pseudomonas

Answer

Legionella

Answer

Pneumococcus

Answer

Coagulase negative staphylococcus

Question 2

What is the typical bacterial count in the duodenum?

Accepted Answer

10^2 per gram

Answer

10^1 per gram

Answer

10^10 per gram

Answer

10^5 per gram

Question 3

Which is the most common bacterial organism causing bacterial upper respiratory tract infections (including sinusitis, otitis media, and pharyngitis) in adults?

Accepted Answer

Streptococcus pneumoniae

Answer

Staphylococcus aureus

Answer

Haemophilus influenzae

Answer

Streptococcus pyogenes

Question 4

Color of granules in mycetoma caused by Actinomadura pelletierrii -

Accepted Answer

Red

Answer

Black

Answer

Yellow

Answer

Brown

Question 5

In a patient presenting with respiratory symptoms, acute angled septate hyphae are seen in which of the following fungi?

Accepted Answer

Aspergillus

Answer

Mucor

Answer

Penicillium

Answer

Candida

Question 6

Patient came from Nagaland and shows positive test with OXK antigen. Diagnosis is?

Accepted Answer

Scrub typhus

Answer

Trench fever

Answer

Endemic typhus

Answer

Epidemic typhus

Question 7

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 8

XDR-TB is defined as resistance to which of the following drug combinations?

Accepted Answer

Fluoroquinolones plus INH plus rifampicin plus amikacin

Answer

INH plus rifampicin

Answer

Fluoroquinolones plus INH plus amikacin

Answer

Fluoroquinolones plus rifampicin plus kanamycin

Question 9

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 10

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

NEET-PG 2013 — Microbiology