Bacteriology — MCQs

Bacteriology Indian Medical PG Practice Questions and MCQs

Question 2421: Which of the following bacteria is not capsulated?

A. Pneumococcus
B. Klebsiella
C. Meningococcus
D. Proteus (Correct Answer)

Explanation: ***Proteus*** - *Proteus* species are **non-capsulated bacteria**; their primary virulence factor is urease production and motility via flagella. - While they can cause infections, the lack of a capsule means they do not evade phagocytosis in the same manner as the other listed options. *Pneumococcus* - **_Streptococcus pneumoniae_**, commonly known as pneumococcus, is a highly **capsulated bacterium**. - Its polysaccharide capsule is a major **virulence factor** that inhibits phagocytosis, contributing to its ability to cause pneumonia, meningitis, and other invasive diseases. *Klebsiella* - **_Klebsiella pneumoniae_** is a **heavily capsulated Gram-negative bacterium** with a prominent polysaccharide capsule. - The thick capsule gives colonies a **mucoid appearance** and serves as a major **virulence factor** that protects against phagocytosis, contributing to pneumonia, UTIs, and other infections. *Meningococcus* - **_Neisseria meningitidis_**, or meningococcus, is a **capsulated bacterium**. - Its **polysaccharide capsule** is vital for immune evasion and is the basis for serogrouping and vaccine development against meningococcal disease.

Question 2422: Darting motility which occurs in V.cholerae, also found in -

A. Campylobacter jejuni (Correct Answer)
B. Bacillus anthracis
C. Shigella
D. Pneumococcus

Explanation: ***Campylobacter jejuni*** - *Campylobacter jejuni* is well-known for its **rapid, corkscrew-like motility**, often described as **darting motility**, which is a key characteristic for its identification. - This characteristic movement is due to its **polar flagella** and helps the bacterium penetrate the intestinal mucosa. *Shigella* - *Shigella* species are notable for being **non-motile**, a crucial feature distinguishing them from other enterobacteriaceae. - Their lack of flagella and motility prevents them from exhibiting darting or any other form of self-propulsion. *Bacillus anthracis* - *Bacillus anthracis* is typically described as **non-motile** in its vegetative form. - While other *Bacillus* species can be motile, *B. anthracis* lacks the flagella necessary for darting motility. *Pneumococcus* - *Pneumococcus* (Streptococcus pneumoniae) is a **non-motile** bacterium. - It does not possess flagella and therefore cannot exhibit darting or any other type of active movement.

Question 2423: Which organism is responsible for producing Draughtsman (Concentric Rings) on culture?

A. Bacillus anthracis (Correct Answer)
B. B. pertussis
C. H. ducreyi
D. Pneumococci

Explanation: ***Bacillus anthracis*** - *Bacillus anthracis* is the organism responsible for producing the characteristic **"Draughtsman" or "Concentric Rings"** pattern on culture media - On blood agar, colonies show a **"Medusa head"** appearance with **concentric rings** and **comma-shaped projections** radiating outward from the center - This distinctive morphology results from chains of bacilli growing in parallel alignment, creating the characteristic pattern - The colonies are typically **non-hemolytic, grey-white, and have irregular edges** *H. ducreyi* - *Haemophilus ducreyi* causes **chancroid** and is difficult to culture - Colonies appear as **small, grey-yellow, translucent** with a **cohesive ("school of fish")** appearance when pushed across the agar - Does not produce concentric rings *B. pertussis* - *Bordetella pertussis* grows on **Bordet-Gengou agar** or **Regan-Lowe medium** - Colonies have a characteristic **"mercury droplet"** or **"bisected pearl"** appearance due to their smooth, shiny, convex morphology - This is completely different from the Draughtsman pattern *Pneumococci* - *Streptococcus pneumoniae* produces **alpha-hemolytic colonies** on blood agar - Colonies are **small, dome-shaped, mucoid** with a **central umbilication** (draughtsman or checker-piece appearance refers to the depression, not concentric rings) - The "draughtsman" term when applied to pneumococci refers to the flattened checker-piece shape, not the concentric ring pattern of *B. anthracis*

Question 2424: Which of the following statements about Corynebacterium diphtheriae is NOT true?

A. Has metachromatic granules
B. Toxin mediated by chromosomal gene (Correct Answer)
C. Toxigenicity demonstrated by elek's test
D. Does not invade deeper tissues

Explanation: ***Toxin mediated by chromosomal gene*** - The **diphtheria toxin** is encoded by the **tox gene**, which is a lysogenic bacteriophage (cornyphage) gene, not a chromosomal gene. - This **bacteriophage** integrates into the bacterial chromosome, making toxigenic *C. diphtheriae* strains lysogenized. *Has metachromatic granules* - *Corynebacterium diphtheriae* is known for possessing **metachromatic granules** (also called Babes-Ernst bodies), which are inclusions that stain differently from the rest of the cell. - These granules are composed of **polyphosphate reserves** and are important for identification. *Does not invade deeper tissues* - *Corynebacterium diphtheriae* remains **localized** to the mucosal surface of the upper respiratory tract or skin, forming a **pseudomembrane**. - Its pathogenicity is primarily due to the **exotoxin** it produces, which then disseminates systemically. *Toxigenicity demonstrated by elek's test* - The **Elek test** is a standard laboratory assay used to determine the **toxigenicity** of *Corynebacterium diphtheriae* strains by detecting the production of diphtheria toxin. - It works by identifying the **immunoprecipitation lines** formed between antitoxin and toxin in an agar medium.

Question 2425: 'String of pearl' colonies on penicillin-containing nutrient agar are produced by:

A. Salmonella
B. Bacillus (Correct Answer)
C. Proteus
D. Klebsiella

Explanation: ***Bacillus*** - The "string of pearls" morphology is a classic characteristic of *Bacillus anthracis* when grown on a nutrient agar containing penicillin. - This appearance is due to the bacterium's cell wall being weakened by penicillin, leading to swollen, elongated cells that remain attached in a chain. *Proteus* - *Proteus* species are known for their characteristic **swarming motility** on agar, not a "string of pearls" appearance. - They are typically **resistant to penicillin** and would not show this inhibited growth pattern. *Salmonella* - *Salmonella* typically forms **smooth, round colonies** on agar and does not exhibit a "string of pearls" morphology. - While some species can be inhibited by penicillin, they do not develop this specific appearance. *Klebsiella* - *Klebsiella* species are typically **mucoid** due to their polysaccharide capsule, forming large, glistening colonies. - They are also often **resistant to penicillin** and would not show the "string of pearls" effect.

Question 2426: Acute Infective Endocarditis with abscess formation is most commonly associated with

A. Listeria
B. Staphylococcus (Correct Answer)
C. Streptococcus
D. Enterococcus

Explanation: ***Staphylococcus*** - **_Staphylococcus aureus_** is the most common cause of **acute infective endocarditis (AIE)** and is particularly virulent, leading to rapid valve destruction and **abscess formation**. - Its ability to adhere to damaged endothelium and produce various toxins contributes to its high pathogenicity and propensity for complicated infections. *Listeria* - **_Listeria monocytogenes_** is a gram-positive rod known to cause meningitis and gastrointestinal infections, especially in immunocompromised individuals. - While it can rarely cause endocarditis, it is not typically associated with the majority of AIE cases or abscess formation. *Streptococcus* - **_Streptococcus_ species**, particularly **_Viridans streptococci_**, are commonly associated with **subacute infective endocarditis (SIE)** on previously damaged valves. - They generally cause a more indolent course and are less frequently linked to rapid valve destruction or abscess formation compared to _Staphylococcus aureus_. *Enterococcus* - **_Enterococcus_ species** are a common cause of endocarditis, especially in older patients, those with healthcare-associated infections, or urinary tract procedures. - While they can cause serious infections, **_Staphylococcus aureus_** remains the predominant pathogen for acute infective endocarditis with abscess formation.

Question 2427: Most common bacterial cause of acute parotitis -

A. Staphylococcus Aureus (Correct Answer)
B. Klebsiella
C. Streptococcus Viridans
D. Streptococcus Pneumoniae

Explanation: ***Staphylococcus Aureus*** - **_Staphylococcus aureus_** is the most frequent bacterial pathogen isolated in cases of **acute bacterial parotitis**. [2] - It often causes ascending infection from the oral cavity, leading to inflammation and suppuration of the parotid gland. [1] *Streptococcus Pneumonia* - While **_Streptococcus pneumoniae_** can cause various infections, it is not the primary cause of acute bacterial parotitis. - Its infections more commonly manifest as **pneumonia**, otitis media, or meningitis. *Klebsiella* - **_Klebsiella_** species are typically associated with **nosocomial infections**, particularly urinary tract infections and pneumonia. - They are a relatively uncommon cause of acute parotitis compared to _S. aureus_. *Streptococcus Viridans* - **_Streptococcus viridans_** group bacteria are common commensal organisms of the oral cavity and are often implicated in **dental caries** and **endocarditis**. - They are not a usual cause of acute bacterial parotitis.

Question 2428: How many flagella does Helicobacter pylori typically have?

A. 4-6 (Correct Answer)
B. 3
C. 2
D. 1

Explanation: ***4-6*** - *Helicobacter pylori* is characterized by having **multiple flagella** (typically 4-6) at one pole, which are crucial for its motility. - These flagella allow the bacterium to move through the viscous gastric mucus layer and colonize the gastric epithelium. *1* - While some bacteria, like *Vibrio cholerae*, may possess a single polar flagellum, this is not characteristic of *Helicobacter pylori*. - A single flagellum would provide less efficient motility in the challenging environment of the stomach. *2* - Having two flagella is not the typical configuration for *Helicobacter pylori*. - Many bacteria have varied flagellar arrangements, but two is not representative of this particular bacterium. *3* - Three flagella is an insufficient number for the characteristic motility and colonization strategy of *Helicobacter pylori*. - **Lophotrichous** flagella typically refers to a tuft of multiple flagella, consistent with 4-6.

Question 2429: What is a key distinguishing feature of meningococci compared to gonococci?

A. Are intracellular pathogens
B. Are catalase positive
C. Ferment maltose (Correct Answer)
D. Possess a capsule

Explanation: ***Ferment maltose*** - *Neisseria meningitidis* ferments both **glucose and maltose**, which is a key biochemical characteristic used for its identification. - *Neisseria gonorrhoeae* only ferments **glucose**, differentiating it from meningococci. *Are intracellular pathogens* - Both **meningococci** (*Neisseria meningitidis*) and **gonococci** (*Neisseria gonorrhoeae*) are facultative intracellular pathogens, meaning they can survive and replicate within host cells. - Therefore, this feature does not distinguish between the two. *Are catalase positive* - Both *Neisseria meningitidis* and *Neisseria gonorrhoeae* are **catalase-positive**, meaning they produce the enzyme catalase. - This characteristic is common to both and thus cannot be used to differentiate them. *Possess a capsule* - While *Neisseria meningitidis* possesses a **polysaccharide capsule**, which is a major virulence factor, *Neisseria gonorrhoeae* typically **lacks a capsule**. - However, the ability to ferment maltose is a more direct and commonly used biochemical distinguishing feature in laboratory settings.

Question 2430: Which of the following organisms does not enter through abrasions in the skin?

A. E rhusiopathiae
B. E corrodens
C. C hominis (Correct Answer)
D. C violaceum

Explanation: ***Chryseobacterium hominis*** - **Chryseobacterium hominis** is primarily a cause of **nosocomial infections**, particularly in immunocompromised patients, and typically enters the body via **medical devices or respiratory route**, not skin abrasions. - It is known to colonize humid environments and medical equipment, leading to **bacteremia**, **meningitis**, or **pneumonia**. - This organism is transmitted through contaminated medical equipment, ventilators, or via the respiratory tract, distinguishing it from the other options. *Erysipelothrix rhusiopathiae* - This organism is a common cause of **erysipelas** or **erysipeloid** in humans, often contracted through contact with infected animals or animal products via **minor skin abrasions**. - The infection typically presents as a **painful, violaceous, spreading skin lesion** at the site of inoculation. - Common in fish handlers, butchers, and veterinarians who sustain occupational skin injuries. *Eikenella corrodens* - **Eikenella corrodens** is a gram-negative rod that is part of the normal oral flora and often causes infections following **human bites** or **fist fights** (clenched-fist injuries), where it enters through **skin abrasions or breaks**. - It is notorious for causing **osteomyelitis** and **abscesses** subsequent to these types of injuries. *Chromobacterium violaceum* - **Chromobacterium violaceum** is a rare but highly pathogenic bacterium found in soil and water in tropical and subtropical regions, entering the body through **breaks in the skin**, such as cuts or abrasions. - Infections are severe and can lead to **sepsis**, **multiple organ abscesses**, and a high mortality rate due to its production of **violacein** and other toxins.

Practice by Chapter

Staphylococci

Practice Questions

Streptococci and Enterococci

Practice Questions

Neisseria and Moraxella

Practice Questions

Corynebacterium and Listeria

Practice Questions

Bacillus and Clostridium

Practice Questions

Enterobacteriaceae

Practice Questions

Vibrio, Aeromonas, and Plesiomonas

Practice Questions

Pseudomonas and Related Bacteria

Practice Questions

Haemophilus and HACEK Group

Practice Questions

Bordetella and Brucella

Practice Questions

Mycobacteria

Practice Questions

Spirochetes

Practice Questions

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