Bacteriology Practice Questions

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.

Q: All are useful in management of patient with infection with the following organism except:

Intramuscular tetanus immunoglobulin. This image depicts a gram stain morphology suggestive of **Clostridium perfringens**, characterized by **gram-positive rods** (the purple lines) and **spores** (the round blue dots). *C. perfringens* is a common cause of **gas gangrene** (myonecrosis). ***Intramuscular tetanus immunoglobulin*** - **Tetanus** is caused by *Clostridium tetani*, not *Clostridium perfringens*. Tetanus immunoglobulin is used to treat or prevent tetanus, which presents with muscle spasms and lockjaw, not gas gangrene. - While both are *Clostridium* species, their pathogenic mechanisms and clinical manifestations are distinct, requiring different specific treatments. *Hyperbaric oxygen* - *Clostridium perfringens* is an **anaerobic bacterium**, meaning it thrives in low-oxygen environments. - **Hyperbaric oxygen therapy** increases tissue oxygen levels, which is highly toxic to *C. perfringens* and can halt toxin production and bacterial growth. *Metronidazole* - **Metronidazole is an antimicrobial highly effective against anaerobic bacteria**, including *Clostridium perfringens*. - It works by disrupting bacterial DNA synthesis and is a crucial part of antibiotic regimens for gas gangrene. *Wound debridement* - Gas gangrene caused by *Clostridium perfringens* involves rapid tissue destruction and necrosis. - **Surgical debridement** is critical for removing infected, necrotic tissue, reducing the bacterial load, and allowing antibiotics and hyperbaric oxygen to be more effective.

Q: All are correct about the organism shown below except:

Phage type A is the commonest worldwide. ***Phage type A is the commonest worldwide*** - While **phage typing** is used for epidemiologic studies of *Mycobacterium tuberculosis*, **phage type A is not recognized as the most common type worldwide**. - Phage typing for *M. tuberculosis* involves using specific bacteriophages to differentiate strains for epidemiological tracking, but the statement about "phage type A" being the commonest is **incorrect**. - This makes it the correct answer for this EXCEPT question. *Obligate aerobe* - *Mycobacterium tuberculosis* is an **obligate aerobe**, meaning it requires oxygen for growth. - This characteristic explains its predilection for oxygen-rich environments in the body, such as the **lungs**. - This statement is **correct**, so it is not the answer to this EXCEPT question. *Dysgonic growth of colonies* - **Dysgonic growth** refers to colonies that grow slowly with a rough, dry, and crumbly appearance, which is characteristic of *M. tuberculosis*. - This slow growth contributes to the **prolonged incubation period** (3-8 weeks) required for culturing the organism in the laboratory. - This statement is **correct**, so it is not the answer to this EXCEPT question. *Niacin test positive for nicotinic acid* - The **niacin accumulation test** (detecting nicotinic acid) is a key biochemical test used to differentiate *Mycobacterium tuberculosis* from other mycobacteria. - *M. tuberculosis* typically accumulates large amounts of **niacin** (nicotinic acid), making this test positive and serving as a positive identifying feature. - This statement is **correct**, so it is not the answer to this EXCEPT question.

Q: All are true about the organism shown except:

Tetanolysin acts on Renshaw cell leading to tetanic spasm. ***Tetanolysin acts on Renshaw cell leading to tetanic spasm*** - **Tetanospasmin**, not tetanolysin, is the neurotoxin produced by *Clostridium tetani* that acts on Renshaw cells to cause muscle spasms. - **Tetanolysin** is a hemolysin that causes tissue damage, which contributes to the anaerobic environment for bacterial growth, but it is not directly responsible for the neurotoxic effects. *Motile bacteria* - *Clostridium tetani* is a **motile** bacterium, possessing peritrichous flagella, which aids in its spread in tissues. - This motility is a characteristic feature of the organism, often observed in laboratory cultures. *Fir tree growth in gelatin stab* - When grown in a gelatin stab culture, *Clostridium tetani* produces a characteristic **"fir tree" or "inverted fir tree" pattern** due to its motility and liquefaction of the gelatin. - This distinctive growth pattern is a classic microbiological identification feature for the organism. *Risus sardonicus* - **Risus sardonicus** (a sustained, involuntary spasm of the facial muscles, causing a characteristic grimace) is a classic clinical manifestation of tetanus caused by **tetanospasmin**. - This symptom is due to the uncontrolled muscle contractions resulting from the neurotoxin's effect on inhibitory neurons.

Q: What is correct about the schematic image of Salmonella typhi?

A=Vi antigen, B=H antigen, C=O antigen. ***A=Vi antigen, B=H antigen, C=O antigen*** - The image correctly identifies A as the **Vi antigen** (capsular polysaccharide), B as the **H antigen** (flagellar protein), and C as the **O antigen** (lipopolysaccharide of the outer bacterial membrane). - These antigens are crucial for the serological classification and pathogenicity of *Salmonella typhi*. *A=H antigen, B=Vi antigen, C=O antigen* - This option incorrectly identifies A as the H antigen and B as the Vi antigen. The **Vi antigen** forms a capsule-like layer, and the **H antigen** is part of the flagella. - The O antigen is correctly identified as part of the outer membrane (C), but the incorrect assignments for A and B make this option wrong. *A=H antigen, B=O antigen, C=Vi antigen* - This option incorrectly identifies A as the H antigen and C as the Vi antigen. The **H antigen** is associated with flagella, not the outermost layer, and the **Vi antigen** is a surface capsule. - The O antigen is also incorrectly assigned to B, which represents the flagella. *A=O antigen, B=Vi antigen, C=H antigen* - This option incorrectly identifies A as the O antigen and C as the H antigen. The **O antigen** is embedded in the outer membrane, not the outermost layer (A). - The **Vi antigen** is incorrectly assigned to B (flagella), and the **H antigen** is incorrectly assigned to C (outer membrane).

Q: A 45-year-old alcoholic presents with severe respiratory distress and red current jelly sputum. On examination bronchial breathing was heard in right infraclavicular and inframammary areas. The X-ray chest is shown below. All are correct about the organism incriminated except:

Indole positive. The clinical presentation of an alcoholic with **severe respiratory distress** and **red currant jelly sputum** is pathognomonic for pneumonia caused by ***Klebsiella pneumoniae***. The chest X-ray showing consolidation in the right upper lobe further supports this diagnosis. The question asks which statement is **INCORRECT** (except) regarding *Klebsiella pneumoniae*. ***Indole positive*** - *Klebsiella pneumoniae* is **indole negative**, not indole positive. This is the incorrect statement. - The indole test detects the production of indole from tryptophan metabolism. *K. pneumoniae* does not produce indole, which differentiates it from *Escherichia coli* (indole positive). - This is a key biochemical differentiator in the Enterobacteriaceae family. *Urease positive* - *Klebsiella pneumoniae* is **urease positive**. This is a correct statement. - Urease production is a characteristic feature used in biochemical identification. - The enzyme hydrolyzes urea to ammonia and carbon dioxide. *Citrate positive* - *Klebsiella pneumoniae* is **citrate positive**. This is a correct statement. - It can utilize citrate as its sole carbon source, demonstrated by the Simmons citrate test. - This is part of the IMViC testing panel. *Voges-Proskauer positive* - *Klebsiella pneumoniae* is **Voges-Proskauer positive**. This is a correct statement. - The VP test detects acetoin production during glucose fermentation. - The standard IMViC profile for *K. pneumoniae* is: Indole (-), Methyl Red (-), Voges-Proskauer (+), Citrate (+). **Key Point:** *Klebsiella pneumoniae* is indole negative, which is the most important biochemical feature distinguishing it from *E. coli* in clinical microbiology.

Q: The given image shows:

Clostridium perfringens. ***Clostridium perfringens*** - This image depicts the **Nagler reaction** (also known as the lecithinase test), which is characteristic of *Clostridium perfringens* - The opaque zone around the bacterial colonies is due to the breakdown of **lecithin** by the alpha-toxin (lecithinase) produced by *C. perfringens* - *C. perfringens* is the classic organism demonstrating a strong positive Nagler reaction *Clostridium botulinum* - *Clostridium botulinum* does not produce lecithinase and would not show a positive Nagler reaction - It is best known for producing **botulinum toxin**, which causes flaccid paralysis *Clostridium tetani* - *Clostridium tetani* is identified by its **tennis-racket spore morphology** and production of tetanus toxin - It does not produce lecithinase, and thus the Nagler reaction would be negative *Clostridium novyi* - While *Clostridium novyi* can produce alpha-toxin, it is not the primary organism for which the Nagler reaction is used for definitive identification - *C. perfringens* remains the classic and most reliable example for this test

Question 1

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 2

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 3

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 4

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

Question 5

All are useful in management of patient with infection with the following organism except:

Accepted Answer

Intramuscular tetanus immunoglobulin

Answer

Hyperbaric oxygen

Answer

Metronidazole

Answer

Wound debridement

Question 6

All are correct about the organism shown below except:

Accepted Answer

Phage type A is the commonest worldwide

Answer

Obligate aerobe

Answer

Dysgonic growth of colonies

Answer

Niacin test positive for nicotinic acid

Question 7

All are true about the organism shown except:

Accepted Answer

Tetanolysin acts on Renshaw cell leading to tetanic spasm

Answer

Motile bacteria

Answer

Fir tree growth in gelatin stab

Answer

Risus sardonicus

Question 8

What is correct about the schematic image of Salmonella typhi?

Accepted Answer

A=Vi antigen, B=H antigen, C=O antigen

Answer

A=H antigen, B=Vi antigen, C=O antigen

Answer

A=H antigen, B=O antigen, C=Vi antigen

Answer

A=O antigen, B=Vi antigen, C=H antigen

Question 9

A 45-year-old alcoholic presents with severe respiratory distress and red current jelly sputum. On examination bronchial breathing was heard in right infraclavicular and inframammary areas. The X-ray chest is shown below. All are correct about the organism incriminated except:

Accepted Answer

Indole positive

Answer

Urease positive

Answer

Citrate positive

Answer

Voges-Proskauer positive

Question 10

The given image shows:

Accepted Answer

Clostridium perfringens

Answer

Clostridium botulinum

Answer

Clostridium tetani

Answer

Clostridium novyi

Bacteriology — MCQs

Bacteriology — MCQs

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