Bacteriology Practice Questions

Q: Neutrophilic granulomatous mastitis is caused by which of the following organisms?

Corynebacterium kroppenstedtii. ***Corynebacterium kroppenstedtii*** - This organism is the most commonly identified cause of **idiopathic granulomatous mastitis (IGM)**, specifically the subtype characterized by **neutrophilic microabscesses** adjacent to **non-caseating granulomas**. - It is a **lipophilic diphtheroid** often isolated from breast aspirates or biopsies of patients with **chronic, relapsing breast inflammation**. *Corynebacterium minutissimum* - This bacterium is primarily associated with **erythrasma**, a superficial skin infection presenting as reddish-brown patches, especially in intertriginous areas. - It is generally not involved in causing deep-seated, chronic granulomatous inflammation or abscess formation within the breast parenchyma. *Mycobacterium tuberculosis* - *M. tuberculosis* causes **tuberculous mastitis**, which is histologically defined by the presence of **caseating granulomas** and large areas of necrosis. - This differs from neutrophilic granulomatous mastitis, which features predominantly **non-caseating granulomas** mixed with neutrophils and microabscesses. *Staphylococcus aureus* - *S. aureus* is the leading cause of **acute mastitis** and **breast abscesses**, characterized by rapid onset, pain, fever, and abundant acute inflammatory cells (pus). - It is typically associated with acute suppurative changes, not the chronic, indolent, granulomatous tissue reaction found in neutrophilic granulomatous mastitis.

Q: In a village, several people developed dysentery after consuming raw milk. On laboratory examination, gram-negative, curved rods with polymorphonuclear infiltration were found in stool samples. Which of the following is the most likely causative organism?

Campylobacter jejuni. ***Campylobacter jejuni*** - This organism is a **Gram-negative, curved or S-shaped rod** (seagull appearance) that causes inflammatory diarrhea (**dysentery**) and is the most common antecedent of **Guillain-Barré Syndrome**. - The association of dysentery with consumption of **raw milk** is a classic epidemiological feature of *C. jejuni* infection, explaining the outbreak. *Clostridium perfringens* - This is a **Gram-positive, spore-forming rod** and causes toxin-mediated food poisoning (Type A) characterized primarily by watery diarrhea, not typically dysentery. - The source is usually contaminated meat and gravies, and the stool sample would show a **Gram-positive rod**, not a curved Gram-negative rod. *Staphylococcus aureus* - This organism is a **Gram-positive coccus** that causes food intoxication with rapid onset vomiting being the prominent feature, not dysentery. - The pathology is preformed toxin-mediated, and stool analysis would reveal **cocci**, not curved rods, and lacks the PMN infiltration typical of dysentery. *Vibrio parahaemolyticus* - While it is a **Gram-negative curved rod**, it is strongly associated with the consumption of **raw or undercooked seafood**, especially shellfish. - Clinically, it usually causes watery diarrhea, and raw milk is not its typical vehicle of transmission for large outbreaks.

Q: Group A Streptococcus is the most common cause of bacterial pharyngitis in school-aged children. Which of the following bacterial components is primarily responsible for its attachment to fibronectin on the epithelial lining of the pharynx?

Lipoteichoic acid. ***Lipoteichoic acid*** - **Lipoteichoic acid (LTA)**, along with the **M protein**, serves as a key adhesin for Group A Streptococcus, mediating attachment by binding to **fibronectin** receptors on pharyngeal epithelial cells. - This adherence mechanism is essential for the initial colonization and subsequent establishment of **streptococcal pharyngitis**. *Lipoprotein* - **Lipoproteins** are structurally diverse cell components, but they are not recognized as the primary molecular component mediating the specific attachment of GAS to **fibronectin**. - They often reside in the cell membrane and typically function in **nutrient transport** or signaling pathways. *Capsule* - The **hyaluronic acid capsule** of Group A Streptococcus mainly functions as an **anti-phagocytic factor** against host immune cells, preventing ingestion. - While important for virulence, it is not the molecule that directly facilitates initial adherence to the **fibronectin** layer of the host epithelium. *Flagella* - **Flagella** are organelles primarily responsible for **bacterial motility** (movement). - *Streptococcus pyogenes* (Group A Streptococcus) is a **non-motile** organism and therefore lacks flagella.

Q: A patient presents with a history of chronic meningitis. Laboratory findings show Gram-positive, filamentous branching bacteria, Positive ZN stain, Growth on paraffin bait culture. Which of the following is the most likely causative organism?

Nocardia asteroides. ***Nocardia asteroides*** - This organism is characterized by **Gram-positive, filamentous, branching bacteria** which are also typically **weakly acid-fast** (Positive ZN stain), differentiating it from Actinomyces. - The ability to utilize paraffin as a sole carbon source and grow on **paraffin bait culture** is a classical diagnostic method specifically employed for identifying **Nocardia** species, fitting the clinical picture of chronic meningitis (Nocardiosis). *Actinomyces israelii* - Although it is a **Gram-positive, filamentous, branching bacterium**, *Actinomyces* is strictly **anaerobic** and is typically **non-acid fast** (ZN negative), which contradicts the lab finding. - It commonly causes chronic suppurative infections like lumpy jaw, often involving **sulfur granules**, and is not diagnosed via paraffin culture methods. *Mycobacterium tuberculosis* - This organism is a major cause of **chronic meningitis** and is **strongly acid-fast** (ZN positive), but its morphology is that of a simple rod (**bacillus**), not a **filamentous branching** structure. - It requires specific media like **Lowenstein-Jensen (LJ) medium** for culture and is not known to grow on paraffin bait. *Cryptococcus neoformans* - This is an encapsulated **yeast (fungus)**, not a bacterium, and therefore does not show **filamentous branching** or Gram-positive bacterial morphology. - Diagnosis is typically made via **India ink stain** or detection of **Cryptococcal antigen** in CSF, not ZN staining or paraffin bait culture.

Q: The Kanagawa phenomenon observed on Wagatsuma agar is characteristic of which of the following organisms?

Vibrio parahaemolyticus. ***Vibrio parahaemolyticus*** - The **Kanagawa phenomenon** describes the ability of certain strains of *Vibrio parahaemolyticus* to produce a **heat-stable direct hemolysin (TDH)**. - This hemolysin causes **beta-hemolysis** (complete clearing) when the organism is grown on a specialized high-salt medium like **Wagatsuma agar**, distinguishing pathogenic strains. *Vibrio cholerae* - This organism causes **cholera** and typically produces yellow colonies on **TCBS agar** (Thiosulfate Citrate Bile Salts Sucrose). - Its primary virulence mechanism is the production of **cholera toxin**, and it does not exhibit the specific Kanagawa phenomenon. *Staphylococcus aureus* - *S. aureus* produces several hemolysins (alpha, beta, delta) but is generally identified using tests like the **coagulase test** and growth on **Mannitol Salt Agar**. - The Kanagawa phenomenon on Wagatsuma agar is a specific test reserved for identifying potentially pathogenic *Vibrio* species. *Burkholderia pseudomallei* - This bacterium causes **melioidosis** and is typically identified by its characteristic **wrinkled colony morphology** on media like Ashdown agar. - It is a Gram-negative bacillus common in Southeast Asia and is not associated with the specific hemolytic action defined by the Kanagawa test.

Q: Which of the following is responsible for green color on antibiotic disk sensitivity testing?

Pyoverdine and pyocyanin. **Pyoverdine and pyocyanin** - The characteristic green color in *Pseudomonas aeruginosa* cultures, as seen in the antibiotic disk sensitivity testing agar, is due to the synergistic production of **pyoverdine** (a fluorescent yellow-green pigment and siderophore) and **pyocyanin** (a blue-green phenazine pigment). - These pigments are **excreted products** that contribute to the organism's distinctive appearance on culture media and are factors in its pathogenicity. *Pneumolysin* - **Pneumolysin** is a **cytotoxin** produced by *Streptococcus pneumoniae*, which is responsible for damaging host cells but does not produce green pigmentation in culture. - It is a key virulence factor in pneumococcal infections, contributing to inflammation and tissue injury, but its presence does not result in a green color on agar. *Optochin* - **Optochin** is an **antibiotic** used to differentiate *Streptococcus pneumoniae* (sensitive) from other alpha-hemolytic streptococci (resistant). - Its action is cidal or static against *S. pneumoniae*, creating a **zone of inhibition** around the disk, but it does not produce any color change on its own. *Alpha hemolysin* - **Alpha hemolysis** refers to the **partial lysis of red blood cells**, resulting in a greenish discoloration around bacterial colonies on blood agar, often seen with *Streptococcus pneumoniae* or viridans streptococci. - While it produces a greenish hue, the strong, pervasive green color observed across the entire agar in the context of antibiotic disk sensitivity testing for organisms like *Pseudomonas aeruginosa* is specifically due to the exopigments pyoverdine and pyocyanin, rather than solely alpha hemolysis.

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.

Question 1

Neutrophilic granulomatous mastitis is caused by which of the following organisms?

Accepted Answer

Corynebacterium kroppenstedtii

Answer

Corynebacterium minutissimum

Answer

Staphylococcus aureus

Answer

Mycobacterium tuberculosis

Question 2

In a village, several people developed dysentery after consuming raw milk. On laboratory examination, gram-negative, curved rods with polymorphonuclear infiltration were found in stool samples. Which of the following is the most likely causative organism?

Accepted Answer

Campylobacter jejuni

Answer

Staphylococcus aureus

Answer

Vibrio parahaemolyticus

Answer

Clostridium perfringens

Question 3

Group A Streptococcus is the most common cause of bacterial pharyngitis in school-aged children. Which of the following bacterial components is primarily responsible for its attachment to fibronectin on the epithelial lining of the pharynx?

Accepted Answer

Lipoteichoic acid

Answer

Capsule

Answer

Flagella

Answer

Lipoprotein

Question 4

A patient presents with a history of chronic meningitis. Laboratory findings show Gram-positive, filamentous branching bacteria, Positive ZN stain, Growth on paraffin bait culture. Which of the following is the most likely causative organism?

Accepted Answer

Nocardia asteroides

Answer

Actinomyces israelii

Answer

Mycobacterium tuberculosis

Answer

Cryptococcus neoformans

Question 5

The Kanagawa phenomenon observed on Wagatsuma agar is characteristic of which of the following organisms?

Accepted Answer

Vibrio parahaemolyticus

Answer

Vibrio cholerae

Answer

Staphylococcus aureus

Answer

Burkholderia pseudomallei

Question 6

Which of the following is responsible for green color on antibiotic disk sensitivity testing?

Accepted Answer

Pyoverdine and pyocyanin

Answer

Pneumolysin

Answer

Optochin

Answer

Alpha hemolysin

Question 7

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 8

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 9

Which is incorrect about the picture shown below?

Accepted Answer

Stimulation of Renshaw cell

Answer

Opisthotonus

Answer

Tetanospasmin

Answer

Laryngospasm

Question 10

The following gram stain shows which bacteria?

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus pneumoniae

Answer

Listeria monocytogenes

Answer

Vibrio cholerae

Bacteriology — MCQs

Bacteriology — MCQs

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