Bacteriology Practice Questions

Q: The image shows a spirochete. Which of the following typically has 5-8 regular spirals with hooked ends?

Leptospira. ***Leptospira*** - *Leptospira* are characterized by their **fine, closely wound spirals** and notably **hooked ends**, typically having 5-8 such tight coils. - They are highly motile and responsible for **leptospirosis**, an infection transmitted through contact with infected animal urine. *Treponema pallidum* - *Treponema pallidum* has **tightly coiled**, regular spirals but generally **lacks the hooked ends** characteristic of *Leptospira*. - This bacterium is the causative agent of **syphilis**, a sexually transmitted infection. *Borrelia* - *Borrelia* species are known for their **loosely coiled**, irregular spirals, which are distinct from the fine and regular coils of *Leptospira*. - They are responsible for diseases like **Lyme disease** (*Borrelia burgdorferi*) and **relapsing fever** (*Borrelia recurrentis*). *Campylobacter* - *Campylobacter* are **spiral-shaped** or **curved rods**, but they are much shorter and have fewer, looser turns than the spirochetes mentioned, not typically described with 5-8 regular spirals. - They are primarily associated with **gastroenteritis** and are not classified as spirochetes.

Q: All are true about the terminal area marked 'X' in this bacteria except:

Strongly eosinophilic. ***Strongly eosinophilic*** - The terminal areas marked 'X' represent **metachromatic granules** (also called volutin granules) which stain reddish-purple with methylene blue, a basic dye, indicating they are **basophilic**, not eosinophilic. - Eosinophilic structures stain well with acidic dyes like eosin, resulting in a pink or red color. *Volutin granules* - The terminal areas marked 'X' are characteristic **volutin granules**, also known as **metachromatic granules**, which are inclusions seen in certain bacteria. - These granules are prominent in *Corynebacterium diphtheriae*, which typically exhibits a **club-shaped** or **cuneiform** morphology. *Function as storage reservoir for phosphate* - Volutin granules primarily serve as a **storage reservoir for inorganic polyphosphate**, which is crucial for the bacterium's energy metabolism and various cellular processes. - This stored phosphate can be utilized when environmental phosphate levels are low. *Also found in Yersinia pestis* - **Bipolar staining**, which resembles prominent granules at the ends of the bacteria (similar to the appearance of volutin granules), is a characteristic feature of *Yersinia pestis*. - This gives *Yersinia pestis* a distinctive "safety pin" appearance on Wright-Giemsa or Wayson stain.

Q: Which is incorrect about the picture shown below?

Stimulation of Renshaw cell. ***Stimulation of Renshaw cell*** - Tetanus toxin (tetanospasmin) **inhibits the release of inhibitory neurotransmitters** (glycine and GABA) from Renshaw cells, preventing them from modulating alpha motor neuron activity. - This **disinhibition leads to sustained muscle contraction** and spasms characteristic of tetanus, such as opisthotonus. *Opisthotonus* - This image clearly depicts **opisthotonus**, a severe spasm of the muscles causing the head and heels to bend backward, and the body to arch forward. - It's a classic sign of **severe tetanus** due to generalized muscle rigidity and uncontrolled muscle spasms. *Tetanospasmin* - The clinical picture of **opisthotonus** is directly caused by **tetanospasmin**, the neurotoxin produced by *Clostridium tetani*. - This toxin blocks the release of inhibitory neurotransmitters, leading to **uncontrolled muscle contractions and spasms**. *Laryngospasm* - **Laryngospasm** is a serious complication of tetanus, involving spasmic closure of the glottis, which can lead to **airway obstruction and asphyxia**. - While not directly depicted, it is a well-known and life-threatening manifestation of severe tetanus caused by the same mechanism as other muscle spasms due to tetanospasmin.

Q: The following gram stain shows which bacteria?

Staphylococcus aureus. ***Staphylococcus aureus*** - The image displays clusters of **Gram-positive cocci**, which is characteristic of *Staphylococcus* species. - While visual identification from a Gram stain alone cannot definitively distinguish *S. aureus* from other staphylococci, this morphology is consistent with *Staphylococcus aureus* (which forms grape-like clusters) and is the most common pathogenic species. *Streptococcus pneumoniae* - *Streptococcus pneumoniae* typically appears as **Gram-positive cocci in pairs (diplococci)** or short chains, not grape-like clusters. - Furthermore, it is often Lancet-shaped and can have a capsule, which is not depicted in the image. *Listeria monocytogenes* - *Listeria monocytogenes* is a **Gram-positive rod**, appearing as short rods, sometimes in pairs or short chains. - The bacteria in the image are clearly cocci, not rods. *Vibrio cholerae* - *Vibrio cholerae* is a **Gram-negative curved rod** or vibrio, meaning it has a comma-like shape and stains pink/red. - The bacteria in the image are cocci and appear purple/blue (Gram-positive) rather than pink/red.

Q: The arrow points to the presence of which bacteria?

Clostridium tetani. ***Clostridium tetani*** - The image displays **long, filamentous bacteria** with **terminal spores**, giving them a classic "tennis racket" or "drumstick" appearance, which is characteristic of *Clostridium tetani*. - *Clostridium tetani* is a **Gram-positive, anaerobic bacillus** known for producing spores, especially in unfavorable conditions. *Streptococcus bovis* - *Streptococcus bovis* (now reclassified as *Streptococcus gallolyticus*) typically appears as **Gram-positive cocci** in chains, rather than long rods with terminal spores. - It is associated with **bacteremia**, endocarditis, and colon cancer, and its morphology does not match the image. *Hemophilus influenzae* - *Hemophilus influenzae* is a **Gram-negative coccobacillus** that can appear as short rods or cocci, often pleomorphic, and does not form spores or long filaments. - This bacterium is a common cause of respiratory infections, otitis media, and meningitis. *Bacillus cereus* - *Bacillus cereus* is a **Gram-positive rod** that forms spores, but these spores are typically **central or subterminal** and do not give the distinctive "tennis racket" morphology seen with *Clostridium tetani*. - It is known for causing **food poisoning** due to enterotoxin production.

Q: Which of the following organisms is incriminated in a patient of left sided endocarditis involving the mitral valve? (Recent NEET Pattern 2016-17)

Streptococcus viridans. ***Streptococcus viridans*** - This group of bacteria is the **most common cause** of **subacute infective endocarditis** on native, previously damaged valves, particularly the mitral valve. - They typically colonize the oral cavity and can enter the bloodstream after dental procedures or poor oral hygiene, leading to seeding of cardiac valves. *Candida albicans* - *Candida albicans* is a common cause of **fungal endocarditis**, which typically presents as a more subacute or chronic illness and can occur in immunocompromised individuals or those with indwelling catheters. - While it can affect the mitral valve, it is less common than bacterial causes, especially in the context of left-sided endocarditis unless specific risk factors (e.g., intravenous drug use, prosthetic valves, prolonged antibiotic use) are present. *Enterococci* - **Enterococcal endocarditis** often occurs in older patients, those with underlying genitourinary or gastrointestinal tract pathology, or healthcare-associated infections. - While they can affect native or prosthetic valves, they are not the most common cause of native valve endocarditis involving the mitral valve in the general population. *Pseudomonas* - **Pseudomonas endocarditis** is typically associated with **intravenous drug use** and commonly affects the **tricuspid valve** (right-sided endocarditis). - While it can involve left-sided valves, it is less frequent in the absence of intravenous drug use compared to *Streptococcus viridans*.

Q: What is incorrect about the bacteria causing the following colonies? (Recent NEET Pattern 2016-17)

Carbon dioxide promotes sporulation. ***Carbon dioxide promotes sporulation*** - This statement is incorrect because **carbon dioxide inhibits sporulation** and promotes the vegetative state of *Bacillus anthracis*. - **Bicarbonate** (often added as sodium bicarbonate) is required for the expression of the capsule in vivo, but not for sporulation. *Medusa head colony* - This is a characteristic appearance of **Bacillus anthracis colonies** on blood agar, often described as having curled margins and irregular projections. - The image provided clearly shows this **distinct morphology**. *Bamboo Rod appearance* - This describes the typical morphology of **Bacillus anthracis** under microscopy, specifically showing **Gram-positive, non-motile rods** arranged in long chains. - This appearance is a key diagnostic feature of the bacteria. *Biological warfare* - *Bacillus anthracis* is a well-known agent for **biological warfare** because its spores are highly stable, easily disseminated, and can cause severe, often fatal, disease (anthrax) upon inhalation. - Its use in bioweapons programs has been documented historically.

Q: Identify the bacteria based on the colony morphology shown in the image.

Bacillus anthracis. ***Bacillus anthracis*** - The image displays characteristic **“Medusa head” colonies** with irregular, wavy margins and a dull, ground-glass appearance, which are classic for *Bacillus anthracis*. - These colonies are often non-hemolytic on blood agar and are notably **non-motile**, a key differentiator from *Bacillus cereus* or *Bacillus subtilis*. *Bacillus subtilis* - While also a *Bacillus* species, *Bacillus subtilis* typically forms **spreading colonies** with a more uniform, often granular or wrinkled texture, distinct from the Medusa head morphology. - It is generally **motile** and can produce various pigments, unlike the non-motile, grayish-white colonies of *B. anthracis*. *Mycoplasma hominis* - *Mycoplasma hominis* forms very tiny colonies, often described as having a **"fried egg" appearance** due to central growth sinking into the agar and a peripheral translucent ring. - These colonies are typically **much smaller** than those seen in the image and require specialized media for growth, making them easily distinguishable. *Mycoplasma pneumoniae* - *Mycoplasma pneumoniae* also produces miniature colonies, typically taking on a **"fried egg" morphology**, but even more fastidious in their growth requirements and size than *M. hominis*. - It would not produce the large, irregular, and distinctly textured colonies observed in the provided image.

Q: Which organism is incriminated in causing the following lesions? (Recent NEET Pattern 2016-17)

Streptococcus pyogenes. ***Streptococcus pyogenes*** - The image depicts **impetigo**, characterized by crusted lesions, often found on the face. - **Streptococcus pyogenes** (Group A Streptococcus) is a common cause of impetigo, either alone or in combination with *Staphylococcus aureus*. *Streptococcus pneumoniae* - *Streptococcus pneumoniae* is primarily associated with **respiratory tract infections**, such as pneumonia and otitis media, not skin lesions like impetigo. - While it can cause invasive diseases, its primary presentation is typically not superficial skin infections. *Enterococcus* - *Enterococcus* species are common inhabitants of the normal **gastrointestinal flora** and are frequently implicated in **urinary tract infections**, endocarditis, and hospital-acquired infections. - They are generally not a primary cause of impetigo or similar superficial skin infections. *Staphylococcus aureus* - While *Staphylococcus aureus* is a very common cause of **impetigo**, the question asks for "the organism" as if there is only one most specific answer without providing other context, suggesting **Streptococcus pyogenes** as a highly relevant primary pathogen, especially if non-bullous impetigo is implied by the crusted appearance. - *S. aureus* often presents with **purulent lesions** (e.g., boils, carbuncles) and bullous impetigo with fluid-filled blisters which eventually rupture and crust.

Q: A 35-year-old male farmer presents with multiple discharging cervical sinuses. Which of these stains will be useful for the diagnosis and where does this organism normally colonize in the body? (AIIMS Nov 2015)

Modified kinyoun acid fast stain, mouth. ***Modified Kinyoun acid-fast stain, mouth*** - This clinical presentation of **multiple discharging cervical sinuses** in a farmer is highly suggestive of **actinomycosis**, caused by *Actinomyces israelii*. - *Actinomyces israelii* is a **Gram-positive, non-spore-forming, anaerobic to microaerophilic rod** that is **partially acid-fast (modified Kinyoun acid-fast stain)** and a normal inhabitant of the **oral cavity, gastrointestinal tract, and female genital tract**. *Gram stain, hypopharynx* - While *Actinomyces israelii* would stain Gram-positive, the **Gram stain** alone is not specific enough to confirm actinomycosis, especially given the characteristic partially acid-fast nature. - The **hypopharynx** is not the primary or most common normal colonization site for *Actinomyces israelii*; the mouth is more accurate. *PAS, intestine* - The **Periodic Acid-Schiff (PAS) stain** is typically used to identify fungi, carbohydrates, and glycogen, not primarily *Actinomyces*. - While *Actinomyces* can be found in the intestine, it's not the most common colonization site associated with cervicofacial actinomycosis. *Grocott methenamine silver stain, vagina* - **Grocott Methenamine Silver (GMS) stain** is primarily used for the detection of fungi and some encapsulated bacteria, but not specifically *Actinomyces*. - Though *Actinomyces* can colonize the vagina, it's more commonly associated with pelvic actinomycosis, not the cervical presentation described.

Question 1

The image shows a spirochete. Which of the following typically has 5-8 regular spirals with hooked ends?

Accepted Answer

Leptospira

Answer

Treponema pallidum

Answer

Borrelia

Answer

Campylobacter

Question 2

All are true about the terminal area marked 'X' in this bacteria except:

Accepted Answer

Strongly eosinophilic

Answer

Volutin granules

Answer

Function as storage reservoir for phosphate

Answer

Also found in Yersinia pestis

Question 3

Which is incorrect about the picture shown below?

Accepted Answer

Stimulation of Renshaw cell

Answer

Opisthotonus

Answer

Tetanospasmin

Answer

Laryngospasm

Question 4

The following gram stain shows which bacteria?

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus pneumoniae

Answer

Listeria monocytogenes

Answer

Vibrio cholerae

Question 5

The arrow points to the presence of which bacteria?

Accepted Answer

Clostridium tetani

Answer

Streptococcus bovis

Answer

Hemophilus influenzae

Answer

Bacillus cereus

Question 6

Which of the following organisms is incriminated in a patient of left sided endocarditis involving the mitral valve? (Recent NEET Pattern 2016-17)

Accepted Answer

Streptococcus viridans

Answer

Candida albicans

Answer

Enterococci

Answer

Pseudomonas

Question 7

What is incorrect about the bacteria causing the following colonies? (Recent NEET Pattern 2016-17)

Accepted Answer

Carbon dioxide promotes sporulation

Answer

Medusa head colony

Answer

Bamboo Rod appearance

Answer

Biological warfare

Question 8

Identify the bacteria based on the colony morphology shown in the image.

Accepted Answer

Bacillus anthracis

Answer

Bacillus subtilis

Answer

Mycoplasma hominis

Answer

Mycoplasma pneumoniae

Question 9

Which organism is incriminated in causing the following lesions? (Recent NEET Pattern 2016-17)

Accepted Answer

Streptococcus pyogenes

Answer

Streptococcus pneumoniae

Answer

Enterococcus

Answer

Staphylococcus aureus

Question 10

A 35-year-old male farmer presents with multiple discharging cervical sinuses. Which of these stains will be useful for the diagnosis and where does this organism normally colonize in the body? (AIIMS Nov 2015)

Accepted Answer

Modified kinyoun acid fast stain, mouth

Answer

Gram stain, hypopharynx

Answer

PAS, intestine

Answer

Grocott methenamine silver stain, vagina

Bacteriology — MCQs

Bacteriology — MCQs

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