Bacteriology Practice Questions

Q: All are correct about the organism shown in the image except: (Recent NEET Pattern 2016-17)

Pneumonic plague is the predominant presentation. **Pneumonic plague is the predominant presentation** - **Bubonic plague** is the most common form of plague, accounting for approximately 80-90% of cases. - While pneumonic plague is highly dangerous and can be transmitted person-to-person, it is **not the predominant clinical form** globally. *Safety pin appearance* - The image shows bipolar staining, which gives *Yersinia pestis* its characteristic **"safety pin" appearance** under microscopy. - This is a classic diagnostic feature when stained with **Giemsa or Wayson stain**. *Direct immunofluorescence for F1 antigen in sputum* - **F1 antigen** is a major virulence factor of *Yersinia pestis* and is produced in large quantities by the bacterium. - **Direct immunofluorescence (DIF)** for detecting F1 antigen in patient samples like sputum is a rapid and specific diagnostic method for plague, especially pneumonic plague. *Doxycycline is used for prophylaxis in house-hold contacts of pneumonic plague* - Due to the high transmissibility and severity of pneumonic plague, **post-exposure prophylaxis (PEP)** is crucial for close contacts. - **Doxycycline** is a recommended antibiotic for PEP alongside other options like ciprofloxacin or levofloxacin.

Q: The following organism shown leads to development of:

Syphilis. ***Syphilis*** - The image displays **spirochetes**, which are characteristic of *Treponema pallidum*, the causative agent of **syphilis**. - **Syphilis** is a sexually transmitted infection that progresses through primary, secondary, latent, and tertiary stages. *Leptospirosis* - Caused by **Leptospira** species, which are also spirochetes but typically have hooked ends and are associated with exposure to contaminated water or animal urine. - Symptoms include fever, headaches, muscle aches, and occasionally severe conditions like Weil's disease (jaundice, renal failure, hemorrhage). *Lyme disease* - Caused by **Borrelia burgdorferi**, another spirochete transmitted by **ticks**. - Characterized by an expanding rash (**erythema migrans**), flu-like symptoms, and can lead to arthritis, neurological problems, and cardiac issues if untreated. *Relapsing fever* - Caused by various species of **Borrelia**, transmitted by **lice or ticks**. - Characterized by recurrent episodes of fever, headache, and muscle pain due to antigenic variation of the bacteria.

Q: The following colony is seen with:

Mycoplasma pneumoniae. ***Mycoplasma pneumoniae*** - The image displays characteristic **"fried egg" colonies**, which are typical for *Mycoplasma pneumoniae* when grown on appropriate agar. This morphology is due to the colony's center growing down into the agar while the periphery spreads on the surface. - This organism is a common cause of **atypical pneumonia** and lacks a cell wall. *Mycoplasma hominis* - While *Mycoplasma hominis* also forms "fried egg" colonies, they are typically **larger** and may develop more rapidly than *M. pneumoniae* colonies. - *M. hominis* is primarily associated with **genitourinary tract infections** and not typically found causing respiratory infections in the general population. *Mycoplasma genitalium* - *Mycoplasma genitalium* colonies are generally **much smaller** and more difficult to observe, often requiring specialized microscopy or staining techniques to visualize due to their extremely slow growth and small size. - This species is mainly implicated in **urogenital infections** like non-gonococcal urethritis. *Mycoplasma fermentans* - *Mycoplasma fermentans* also produces "fried egg" shaped colonies, but they are generally **smaller and less distinct** than those of *M. pneumoniae*. - This species has been associated with various conditions, including **arthritis** and opportunistic infections in immunocompromised individuals, but its colony morphology is not as classically defined as the "fried egg" for *M. pneumoniae* in typical clinical identification.

Q: A 35-year-old patient presents to the OPD 24 hours after a fight with a stranger in which he was bitten. GCS is 15/15 and following injury is noted on left forearm. He complains of extreme pain and tenderness in the injury. Swab from the injury was plated in chocolate agar and incubated in 10% carbon dioxide for 48 hours. Small colonies with pitting appearance were noted. Which of the following organism is responsible?

Eikenella corrodens. ***Eikenella corrodens*** - The context of a **human bite wound** and the characteristic **pitting of agar** by bacterial colonies are classic identifiers for *Eikenella corrodens*. - This organism is a common inhabitant of the **oral flora** and is frequently implicated in infections resulting from human bites. *Flavobacterium meningosepticum* - This organism is more commonly associated with **nosocomial infections**, particularly in newborns and immunocompromised patients, and severe infections like meningitis or sepsis, not typically human bite wounds. - While it can grow on chocolate agar, its colonial morphology does **not typically involve pitting** of the agar. *Capnocytophaga gingivalis* - This organism is also part of the normal oral flora and can cause infections related to human bites, especially in immunocompromised individuals. - However, while it can grow on chocolate agar, it characteristically exhibits **gliding motility** and ferments carbohydrates, but does not typically cause the striking **pitting** seen with *Eikenella corrodens*. *Streptobacillus moniliformis* - *Streptobacillus moniliformis* is associated with **rat bite fever** (Haverhill fever if contracted through contaminated food or water) and not typically human bite wounds. - It often produces **"fried egg" colonies** with a dense center and a lacy edge, which is distinct from the pitting observed here.

Q: All are true about the organism whose colonies are shown below except:

Warm agglutinin production. ***Warm agglutinin production*** - This is the **EXCEPTION** - Mycoplasma pneumoniae produces **COLD agglutinins**, not warm agglutinins - **Cold agglutinins** are IgM antibodies that agglutinate red blood cells at temperatures below 37°C and are a characteristic feature of **Mycoplasma pneumoniae** infection - **Warm agglutinins** are associated with autoimmune hemolytic anemia, not Mycoplasma infections - This is the FALSE statement, making it the correct answer in this EXCEPT question *Mulberry shaped colony* - **TRUE statement** - Mycoplasma colonies have a characteristic **"fried egg" or mulberry appearance** with a dense central zone and a flat peripheral zone - This distinctive colony morphology is due to the organisms growing into the agar surface while spreading on top - This is a key identifying feature of Mycoplasma species on culture media *Lack cell wall* - **TRUE statement** - Mycoplasma are unique among bacteria in that they **completely lack a cell wall** - This absence of cell wall makes them resistant to **beta-lactam antibiotics** (penicillins, cephalosporins) that target cell wall synthesis - The lack of cell wall also contributes to their **pleomorphism** (variable shape) and osmotic fragility - Their cell membrane contains **sterols**, which is unusual for prokaryotes *Divide by binary fission* - **TRUE statement** - Mycoplasma reproduce by **binary fission**, the standard method of bacterial reproduction - Despite lacking a cell wall, they still undergo typical prokaryotic cell division - They are the **smallest self-replicating organisms** capable of independent growth

Q: A blood smear from a patient with fever shows the following spirochetes on microscopy. Identify the organism:

Borrelia. ***Borrelia*** - The image distinctly shows **large, coarse, and irregularly coiled spirochetes**, which are characteristic morphological features of *Borrelia* species. These are larger than other spirochetes and their coils are less tightly wound. - *Borrelia* species cause diseases like **Lyme disease** (*B. burgdorferi*) and **relapsing fever** (*B. recurrentis*), which are diagnosed by identifying these distinctive spirochetes in blood smears or tissue samples. *Treponema pallidum* - This bacterium is characterized by **thinner, tightly coiled, and regularly spaced spirals**, appearing more delicate than the organisms shown in the image. - **Darkfield microscopy** is typically used for direct visualization of *Treponema pallidum* due to its thinness and inability to be stained by Gram stain. *Leptospira* - *Leptospira* are typically **thin, tightly coiled spirochetes** with characteristic **hooked ends**, which are not visible in the provided image. - They are known for causing **leptospirosis**, a zoonotic disease. *Brucella* - *Brucella* are **small, Gram-negative coccobacilli** and are not spirochetes at all. - They cause **brucellosis**, which is a systemic infection with different microscopic appearances.

Q: The following plate shows *H. influenzae* colonies. Which of the following is responsible for the phenomenon shown? (Recent NEET Pattern 2016-17)

V factor. ***V factor*** - The phenomenon depicted is **satellitism**, where *Haemophilus influenzae* grows as satellite colonies around a streak of *Staphylococcus aureus* on blood agar. - This occurs because *S. aureus* lyses red blood cells and releases **V factor (NAD - nicotinamide adenine dinucleotide)**, which is an essential growth factor that *H. influenzae* requires but cannot synthesize. - While *H. influenzae* requires both **X factor (hemin)** and **V factor (NAD)**, the satellitism phenomenon specifically demonstrates the role of **V factor** provided by *S. aureus*. - X factor is already available throughout the blood agar from lysed RBCs, so the enhanced growth specifically around *S. aureus* colonies is due to the **V factor** produced by the bacteria. *X factor* - **X factor (hemin)** is present throughout the blood agar medium from lysed red blood cells, so it does not explain the specific satellite growth pattern around *S. aureus* colonies. - Both X and V factors are required for growth, but the satellitism pattern demonstrates V factor dependency specifically. *PRP antigen* - **PRP (polyribosylribitol phosphate)** is the capsular polysaccharide of *Haemophilus influenzae* type b (Hib) and is a virulence factor. - It is not a growth factor and plays no role in the satellitism phenomenon. *All of the above* - Incorrect, as only **V factor** is responsible for the satellitism phenomenon shown in the image. - PRP antigen is not a growth factor, and X factor is already uniformly distributed in blood agar.

Q: Which of the bacteria is shown in this culture plate of nutrient agar? (Recent NEET Pattern 2016-17)

Pseudomonas. ***Pseudomonas*** - The image displays colonies with a **metallic sheen** and a characteristic **greenish-blue pigment**, consistent with *Pseudomonas aeruginosa* growth on nutrient agar. - This pigmentation is due to the production of **pyocyanin** and **pyoverdin**, which are distinctive for *Pseudomonas aeruginosa*. *Plesiomonas* - *Plesiomonas shigelloides* typically does not produce the intense metallic sheen or the characteristic greenish-blue pigment seen in the image. - It is more commonly associated with aquatic environments and gastrointestinal infections, and its colonies usually appear opaque or translucent. *Burkholderia* - *Burkholderia* species can produce a variety of colony morphologies, but they generally do not exhibit the striking **metallic sheen** or the specific greenish-blue pigmentation caused by pigments like pyocyanin. - Certain *Burkholderia* species, such as *B. cepacia*, might produce yellow or green pigments, but the overall appearance in the image is more typical of *Pseudomonas*. *Pasteurella* - *Pasteurella* species typically produce smaller, gray, translucent, and non-hemolytic colonies without the distinctive **metallic sheen** or pigment seen in the culture image. - They are also facultatively anaerobic and are often associated with respiratory infections in animals and humans after animal bites.

Q: All are correct about the organism shown except:

Inaba serotype has A and B antigens. ***Inaba serotype has A and B antigens*** - This statement is **INCORRECT** and is the right answer to this "EXCEPT" question. - The **Inaba serotype** of *Vibrio cholerae* has only **antigens A and C**, NOT A and B. - The three serotypes of *V. cholerae* O1 are: - **Ogawa:** A, B, C antigens - **Inaba:** A, C antigens (lacks B antigen) - **Hikojima:** A, B, C antigens (rare) *Fish in stream appearance* - This is a **CORRECT** characteristic of *Vibrio cholerae*. - Refers to the microscopic appearance in **hanging drop preparation** where bacteria show rapid darting motility in parallel streams. - This characteristic movement is due to the **single polar flagellum**. *Funnel shaped liquefaction in gelatin stab* - This is a **CORRECT** characteristic of *Vibrio cholerae*. - *V. cholerae* produces the enzyme **gelatinase**, which liquefies gelatin. - In gelatin stab culture, this creates a characteristic **funnel-shaped (infundibuliform) liquefaction** starting from the top. *Red reaction* - This is a **CORRECT** characteristic of *Vibrio cholerae*. - The "red reaction" refers to a **positive oxidase test**. - Indicates the presence of **cytochrome c oxidase** enzyme. - The test uses tetramethyl-p-phenylenediamine dihydrochloride reagent, which turns red/purple when positive.

Q: A 50-year-old village agricultural worker got a dental treatment from a quack for painful dental caries. He later developed a cheek swelling with pus discharge from sinus containing yellow specks. The specks were crushed between two slides and stained with gram stain and ZN stain. All are true about the incriminating organism except:

Environmental saprophytes. ***Environmental saprophytes*** - *Actinomyces israelii* is the primary causative agent of **actinomycosis**, and it is part of the **normal flora of the oral cavity**, gastrointestinal tract, and female genital tract. - It is an **endogenous infection**, meaning it originates from the body's own commensal bacteria, and is not acquired from the environment as a saprophyte. *Sun ray appearance* - The **sulfur granules**, characteristic of *Actinomyces* infections, often demonstrate a **"sun ray" or "rosette" appearance** when viewed under a microscope, due to the radiating filaments at the periphery. - These granules are microcolonies of the organism embedded in host material and are a key diagnostic feature of **actinomycosis**. *A. israelii grows as fluffy balls in BHI agar* - When cultured on **Brain Heart Infusion (BHI) agar**, *Actinomyces israelii* typically produces distinct colonial morphologies, often described as fluffy balls or **"mulberry-like" colonies** after extended anaerobic incubation. - This morphology is a characteristic feature aiding in the laboratory identification of the organism. *Spider colonies of A. israelii* - On solid culture media after initial isolation, *Actinomyces israelii* often forms **characteristic "spider-like" colonies** with irregular, filamentous projections. - This colonial morphology is quite distinct and helps in differentiating it from other bacteria during laboratory diagnosis.

Question 1

All are correct about the organism shown in the image except: (Recent NEET Pattern 2016-17)

Accepted Answer

Pneumonic plague is the predominant presentation

Answer

Safety pin appearance

Answer

Direct immunofluorescence for F1 antigen in sputum

Answer

Doxycycline is used for prophylaxis in house-hold contacts of pneumonic plague

Question 2

The following organism shown leads to development of:

Accepted Answer

Syphilis

Answer

Leptospirosis

Answer

Lyme disease

Answer

Relapsing fever

Question 3

The following colony is seen with:

Accepted Answer

Mycoplasma pneumoniae

Answer

Mycoplasma hominis

Answer

Mycoplasma genitalium

Answer

Mycoplasma fermentans

Question 4

A 35-year-old patient presents to the OPD 24 hours after a fight with a stranger in which he was bitten. GCS is 15/15 and following injury is noted on left forearm. He complains of extreme pain and tenderness in the injury. Swab from the injury was plated in chocolate agar and incubated in 10% carbon dioxide for 48 hours. Small colonies with pitting appearance were noted. Which of the following organism is responsible?

Accepted Answer

Eikenella corrodens

Answer

Flavobacterium meningosepticum

Answer

Capnocytophaga gingivalis

Answer

Streptobacillus moniliformis

Question 5

All are true about the organism whose colonies are shown below except:

Accepted Answer

Warm agglutinin production

Answer

Mulberry shaped colony

Answer

Lack cell wall

Answer

Divide by binary fission

Question 6

A blood smear from a patient with fever shows the following spirochetes on microscopy. Identify the organism:

Accepted Answer

Borrelia

Answer

Treponema pallidum

Answer

Leptospira

Answer

Brucella

Question 7

The following plate shows *H. influenzae* colonies. Which of the following is responsible for the phenomenon shown? (Recent NEET Pattern 2016-17)

Accepted Answer

V factor

Answer

X factor

Answer

All of the above

Answer

PRP antigen

Question 8

Which of the bacteria is shown in this culture plate of nutrient agar? (Recent NEET Pattern 2016-17)

Accepted Answer

Pseudomonas

Answer

Plesiomonas

Answer

Burkholderia

Answer

Pasteurella

Question 9

All are correct about the organism shown except:

Accepted Answer

Inaba serotype has A and B antigens

Answer

Fish in stream appearance

Answer

Funnel shaped liquefaction in gelatin stab

Answer

Red reaction

Question 10

A 50-year-old village agricultural worker got a dental treatment from a quack for painful dental caries. He later developed a cheek swelling with pus discharge from sinus containing yellow specks. The specks were crushed between two slides and stained with gram stain and ZN stain. All are true about the incriminating organism except:

Accepted Answer

Environmental saprophytes

Answer

Sun ray appearance

Answer

A. israelii grows as fluffy balls in BHI agar

Answer

Spider colonies of A. israelii

Bacteriology — MCQs

Bacteriology — MCQs

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