Which of the following is not a sporicidal agent?
What is the most common cause of acute tonsillitis?
What is the most common cause of a peritonsillar abscess?
Empyema thoracis is most commonly caused by which organism
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?
The difference between contamination and infection is that in infection
NEET-PG 2013 - Microbiology NEET-PG Practice Questions and MCQs
Question 91: Which of the following is not a sporicidal agent?
- A. Formaldehyde
- B. Glutaraldehyde
- C. Ethylene oxide
- D. Isopropyl alcohol (Correct Answer)
Explanation: ***Isopropyl alcohol*** - Isopropyl alcohol is an **antiseptic** and **disinfectant** that works by denaturing proteins and dissolving lipids, but it is not effective against bacterial spores. - Its efficacy against microbes is primarily for **vegetative bacteria**, fungi, and enveloped viruses. *Formaldehyde* - Formaldehyde is a potent **sporicide** that cross-links proteins and nucleic acids, making it effective for high-level disinfection and sterilization. - It is often used in solutions or as a gas for sterilizing heat-sensitive medical equipment. *Glutaraldehyde* - Glutaraldehyde is a **high-level disinfectant** and **sterilant** that works by alkylating protein and nucleic acid components, effectively killing spores. - It's commonly used for sterilizing endoscopic instruments and other heat-sensitive devices. *Ethylene oxide* - Ethylene oxide is a gaseous sterilant that **alkylates proteins** and nucleic acids, making it highly effective against all microorganisms, including spores, bacteria, and viruses. - It is frequently used for sterilizing heat-sensitive and moisture-sensitive medical devices.
Question 92: What is the most common cause of acute tonsillitis?
- A. Streptococcus pneumoniae
- B. H. influenzae
- C. Staphylococcus aureus
- D. Group A beta-hemolytic streptococci (Correct Answer)
Explanation: ***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.
Question 93: What is the most common cause of a peritonsillar abscess?
- A. Streptococcus pneumoniae
- B. Staphylococcus aureus
- C. H. influenzae
- D. Group A beta-hemolytic streptococcus (Correct Answer)
Explanation: ***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**.
Question 94: Empyema thoracis is most commonly caused by which organism
- A. Streptococcus pneumoniae (Correct Answer)
- B. Pseudomonas
- C. Staphylococcus aureus
- D. Mycobacterium
Explanation: ***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
Question 95: 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?
- A. H. pylori (Correct Answer)
- B. V. cholerae
- C. H. influenzae
- D. K. pneumoniae
Explanation: ***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 96: The difference between contamination and infection is that in infection
- A. Infectious agent is on body surface (arthropods)
- B. Infectious agent is on body surface or on non-human objects
- C. Infectious agent is on clothes
- D. Infectious agent is in the body of human (Correct Answer)
Explanation: ***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.