Microbiology in Autopsies — MCQs
Arrange the following in sequential order with regards to the steps of collection of samples for pap smear testing: Use posterior vaginal wall retractor Take the sample Make smear on a slide Fix the smear
Autopsy finding after 24 hours in a case of death due to myocardial infarction is
Which parameter in vitreous humor is most commonly used to estimate the time since death?
Which among the following organisms is detected by the "hanging drop preparation"?
A patient with large, penetrating vegetations on his mitral and aortic valves develops severe headaches. Funduscopic examination reveals papilledema. CT scan of the brain demonstrates a ring-enhancing lesion. Which of the following organisms is the most likely cause of the patient's disorder?
Which of the following statements about sudden infant death syndrome (SIDS) is false?
Antemortem diagnosis of rabies is made with:
All tests are used to detect live bacteria, except:
What are the reasons a sample may be disqualified for culture?
Method of autopsy in which organs of various systems are removed en masse:
Microbiology in Autopsies Indian Medical PG Practice Questions and MCQs
Question 1: Arrange the following in sequential order with regards to the steps of collection of samples for pap smear testing: Use posterior vaginal wall retractor Take the sample Make smear on a slide Fix the smear
- A. 1,2,4,3
- B. 3,1,2,4
- C. 1,2,3,4 (Correct Answer)
- D. 2,1,3,4
Explanation: ***1,2,3,4*** - The correct sequence for collecting a Pap smear involves first **visualizing the cervix** using a posterior vaginal wall retractor, then **taking the sample** (e.g., using a broom or spatula and brush), followed by **making a smear on a slide** and finally **fixing the smear** to preserve the cells. - This sequential order ensures proper cell collection and preservation for accurate cytological examination. *1,2,4,3* - This option incorrectly places **fixing the smear** before **making the smear on the slide**. Cells must first be spread onto the slide before they can be fixed. - Fixing an un-smeared sample or attempting to smear after fixing would lead to an inadequate or damaged specimen. *3,1,2,4* - This sequence incorrectly starts with **making a smear on a slide** before any sample has been collected or the cervix visualized. - One cannot make a smear without first taking a sample and accessing the cervix via a retractor. *2,1,3,4* - This option incorrectly states that **taking the sample** occurs before **using a posterior vaginal wall retractor**. The retractor is essential for proper visualization and access to the cervix to obtain a quality sample. - Attempting to take a sample without proper visualization would lead to an inadequate or incorrect specimen collection.
Question 2: Autopsy finding after 24 hours in a case of death due to myocardial infarction is
- A. Coagulative necrosis. (Correct Answer)
- B. Fat necrosis.
- C. Liquefactive necrosis.
- D. Caseous necrosis.
Explanation: ***Coagulative necrosis*** - Coagulative necrosis is the predominant histological finding after **myocardial infarction**, typically occurring within the first 12 hours [1]. - It results in preserved tissue architecture with **cellular outlines** remaining visible, indicating ischemic tissue damage [1,2]. *Liquefactive necrosis* - Commonly associated with **bacterial infections** or brain infarction, it leads to the transformation of tissue into liquid pus, which is not characteristic of myocardial infarction. - It occurs later and is not typically observed in heart tissue within 12 hours post-infarction. *Fat necrosis* - Primarily occurs due to damage to **adipose tissue**, as seen in cases of pancreatitis or trauma, and is not relevant to myocardial injury. - It is characterized by the release of **lipases** and fatty acids, a response not seen in myocardial infarction. *Caseous necrosis* - Often associated with **tuberculosis** or fungal infections, presenting as cheese-like necrotic tissue, it is not a feature of myocardial infarction. - This type of necrosis appears much later and reflects chronic granulomatous inflammation rather than acute ischemic damage. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Heart, p. 552. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Heart, pp. 552-554.
Question 3: Which parameter in vitreous humor is most commonly used to estimate the time since death?
- A. K+ level (Correct Answer)
- B. Urea level
- C. Na+ level
- D. Glucose level
Explanation: ***K+ level*** - After death, cell membranes lose their integrity, leading to a steady leakage of **potassium ions** from intracellular to extracellular compartments, including the vitreous humor. - The rate of increase in **vitreous potassium** is relatively predictable and is thus a reliable indicator for estimating the **post-mortem interval (PMI)**. *Urea level* - While urea is present in vitreous humor, its post-mortem changes are not as consistent or well-defined for precise **PMI estimation** compared to potassium. - Urea levels are more influenced by pre-mortem renal function and other physiological factors, making it less reliable. *Na+ level* - **Sodium ion** concentrations in the vitreous humor tend to be relatively stable after death for a longer period compared to potassium. - The changes are not as pronounced or as linearly progressive as potassium, making it a less accurate marker for early **PMI estimation**. *Glucose level* - **Vitreous glucose** levels decrease rapidly after death due to continued glycolysis by residual cells and microorganisms. - While the decrease is significant, it's highly variable and influenced by factors like environmental temperature and bacterial contamination, making it less consistent for precise **PMI estimation**.
Question 4: Which among the following organisms is detected by the "hanging drop preparation"?
- A. Trichomonas vaginalis (Correct Answer)
- B. Mobiluncus
- C. Candida albicans
- D. Gardnerella vaginalis
Explanation: ***Trichomonas vaginalis*** - The "hanging drop preparation" is a microscopic technique primarily used to detect the **motility** of microorganisms. - **_Trichomonas vaginalis_** is a flagellated protozoan that exhibits characteristic **jerky motility**, which is easily observed in a hanging drop preparation of vaginal discharge. *Candida albicans* - **_Candida albicans_** is a yeast that can be identified in wet mount preparations by observing **yeast cells**, **pseudohyphae**, and **hyphae**. - It does not exhibit the same type of **motility** that makes hanging drop ideal for _Trichomonas_. *Mobiluncus* - **_Mobiluncus_** is a curved, Gram-variable rod that is associated with **bacterial vaginosis**. - While it can be motile, its detection is typically based on **Gram stain** morphology and its association with clue cells and a positive whiff test, not primary identification via hanging drop for motility. *Gardnerella vaginalis* - **_Gardnerella vaginalis_** is a Gram-variable rod considered a key bacterium in **bacterial vaginosis**. - It is identified microscopically as small coccobacillary organisms often coating epithelial cells (**clue cells**) in a **wet mount**, not primarily by its motility in a hanging drop.
Question 5: A patient with large, penetrating vegetations on his mitral and aortic valves develops severe headaches. Funduscopic examination reveals papilledema. CT scan of the brain demonstrates a ring-enhancing lesion. Which of the following organisms is the most likely cause of the patient's disorder?
- A. Herpesvirus
- B. Streptococcus pneumoniae
- C. Mycobacterium tuberculosis
- D. Staphylococcus aureus (Correct Answer)
Explanation: ***Staphylococcus aureus*** - This organism is a common cause of **infective endocarditis**, particularly in patients with intravenous drug use, and is known for producing **large, destructive vegetations** that can readily embolize [2]. - The development of **severe headaches**, **papilledema**, and a **ring-enhancing brain lesion** strongly suggests a **septic embolism** leading to a **brain abscess**, a known complication of infective endocarditis caused by virulent organisms like *S. aureus* [1], [2]. *Herpesvirus* - Herpesvirus infections, such as **HSV-1**, can cause **encephalitis**, which might present with headaches and neurological signs, but they are not typically associated with **infective endocarditis** or the formation of **septic emboli** from heart valves. - While herpes encephalitis can cause ring-enhancing lesions in specific brain regions (e.g., temporal or frontal lobes), the primary presentation here points to a systemic embolic source from the heart. *Streptococcus pneumoniae* - *Streptococcus pneumoniae* can cause endocarditis, though it is less common than *Staphylococcus aureus* and often occurs in patients with pre-existing valvular disease. - While septic emboli can occur, *S. pneumoniae* endocarditis is not as frequently associated with **large, destructive vegetations** and subsequent brain abscess formation as *S. aureus* [2]. *Mycobacterium tuberculosis* - **Tuberculous meningitis** can cause severe headaches, papilledema, and ring-enhancing lesions (tuberculomas) in the brain. - However, **tuberculous_endocarditis** is extremely rare and typically does not manifest with large, destructive vegetations or, more importantly, with a primary infectious source from the heart valves as indicated by the "large, penetrating vegetations."
Question 6: Which of the following statements about sudden infant death syndrome (SIDS) is false?
- A. Seen in premature babies
- B. Peak incidence is between 2-4 months of age
- C. Cause is prolonged breast feeding (Correct Answer)
- D. Occurs only in male children
Explanation: ***Cause is prolonged breast feeding*** - This statement is **false** because **breastfeeding** is actually considered a **protective factor** against SIDS, not a cause. - The longer an infant is breastfed, the lower the risk of SIDS. - Studies consistently show that breastfed infants have a **36-50% reduced risk** of SIDS. *Peak incidence is between 2-4 months of age* - This statement is **true** because SIDS most commonly occurs between **2-4 months of age**. - Over 90% of SIDS cases occur within the **first 6 months of life**. - The peak incidence is at **2-3 months** of age. *Seen in premature babies* - This statement is **true** because **prematurity** is a well-established **risk factor** for SIDS. - Premature infants have underdeveloped neurological and respiratory control systems. - Low birth weight and prematurity increase SIDS risk **2-3 fold**. *Occurs only in male children* - This statement is **false** because **SIDS affects both male and female infants**. - While there is a slight male predominance (approximately **60% male vs 40% female**), SIDS is **not exclusive to males**.
Question 7: Antemortem diagnosis of rabies is made with:
- A. Inoculation in culture media
- B. Negri bodies in hippocampus
- C. Corneal impression smear (Correct Answer)
- D. Rabies virus specific antibodies
Explanation: ***Corneal impression smear*** - A **corneal impression smear** can detect viral antigens in the cornea using fluorescent antibody staining, a method that can be performed on living patients. - This technique provides a relatively rapid and non-invasive way to diagnose rabies **antemortem**. *Inoculation in culture media* - Rabies virus is notoriously difficult to culture in standard cell culture media, making this method impractical and unreliable for **antemortem diagnosis**. - While viral isolation is possible in specialized research settings, it is not a routine diagnostic tool for rabies in living patients. *Negri bodies in hippocampus* - **Negri bodies** are eosinophilic inclusions found in the cytoplasm of neurons, particularly in the hippocampus, which are pathognomonic for rabies. - However, their detection requires **postmortem brain tissue biopsy**, making this a **postmortem diagnostic** method, not antemortem. *Rabies virus specific antibodies* - While the presence of **rabies virus-specific antibodies** (particularly in CSF) can indicate exposure and infection, they often appear late in the disease course. - The detection of antibodies may not be reliable for early **antemortem diagnosis**, especially in naive individuals whose immune response has not yet fully developed.
Question 8: All tests are used to detect live bacteria, except:
- A. Gram staining
- B. ELISA for antibodies (Correct Answer)
- C. Blood culture
- D. Direct microscopy with vital stains
Explanation: ***Correct: ELISA for antibodies*** - **ELISA (Enzyme-linked immunosorbent assay)** for antibodies detects the **host's immune response** to an infection, not the bacteria themselves - This test identifies **antibodies** (IgM, IgG, IgA) produced by the immune system in response to bacterial antigens - **Does NOT detect bacteria** (live or dead) - it detects the immunological memory of exposure - Antibody presence indicates past or current exposure but tells us nothing about the presence of live organisms *Incorrect: Gram staining* - **Gram staining** is primarily a **morphological identification tool** that visualizes bacteria under microscopy - While it stains both live and dead bacteria equally, it is **used clinically to detect bacteria in specimens** (CSF, pus, sputum) - In the context of bacterial detection methods, seeing bacteria on Gram stain from a clinical specimen indicates bacterial presence and guides immediate therapy - Though not a specific viability test, it demonstrates bacterial presence in the sample being examined *Incorrect: Blood culture* - **Blood culture** involves inoculating blood into growth media and incubating to allow bacterial multiplication - **Only viable (live) bacteria will grow** in culture media - this is the gold standard for detecting live bacteria in bloodstream infections - Growth in culture definitively confirms the presence of living, metabolically active bacteria *Incorrect: Direct microscopy with vital stains* - **Vital stains** (e.g., acridine orange, fluorescein diacetate) are dyes that differentiate living cells from dead cells - These stains rely on **metabolic activity** or **intact cell membrane** to distinguish viable organisms - Used in direct microscopy to specifically identify **live bacteria** based on their ability to take up or exclude certain dyes
Question 9: What are the reasons a sample may be disqualified for culture?
- A. Sample brought within 2 hr of collection
- B. Sample brought in sterile plastic container
- C. Sample brought in formalin (Correct Answer)
- D. Sample obtained after cleaning the collection site
Explanation: ***Sample brought in formalin*** - Formalin is a **fixative** that will kill any viable **microorganisms** present in the sample, rendering it unsuitable for culture because no growth will occur. - The purpose of a culture is to identify living organisms; a fixed sample prevents this crucial step. *Sample brought within 2 hr of collection* - This is an **ideal scenario** for sample integrity, as it minimizes the time for degradation or overgrowth of contaminants. - **Prompt transport** ensures the viability of fastidious organisms and accurate representation of the original microbial load. *Sample brought in sterile plastic container* - Using a **sterile container** is essential for preventing **contamination** from external sources. - A non-sterile container would introduce environmental microbes, leading to misleading culture results. *Sample obtained after cleaning the collection site* - **Cleaning the collection site** reduces the presence of **normal flora** or skin contaminants. - This practice helps to ensure that any organisms grown in culture are more likely to be pathogens from the infection site rather than surface contaminants.
Question 10: Method of autopsy in which organs of various systems are removed en masse:
- A. Lettulle (Correct Answer)
- B. Virchow
- C. Rokitansky
- D. Ghon
Explanation: ***Lettulle*** - The **Lettulle method** (or en masse method) involves the removal of organs in large blocks or as a single unit, which helps preserve anatomical relationships. - This technique is particularly useful for studying the **interrelationships between organs** and the spread of disease involving multiple systems. *Virchow* - The **Virchow method** involves the individual removal of each organ, which allows for detailed examination of each organ separately. - This method is straightforward but can disrupt the **anatomical relationships** between organs. *Rokitansky* - The **Rokitansky method** involves *in situ* dissection of organs, with the organs remaining largely in the body during dissection. - This technique is valued for maintaining the **topographical integrity** of organ systems within the body cavity. *Ghon* - The **Ghon method** is a modified block dissection method, focusing on the removal of specific organ blocks. - This often includes the **thoracic and abdominal organs** together, maintaining their anatomical connections.
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