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: Which bacterium is known for forming irregular, rough colonies on culture media?

A. Streptococcus pyogenes
B. Bacillus anthracis
C. Staphylococcus aureus
D. Corynebacterium diphtheriae (Correct Answer)

Explanation: ***Corynebacterium diphtheriae*** - This bacterium is known for forming **irregular**, **rough**, and **dry colonies** on culture media. - On **Loeffler's serum agar**, colonies appear grayish-white with irregular edges and a rough, granular surface. - On **cysteine-tellurite blood agar**, colonies are black or gray with a characteristic irregular, rough morphology often described as resembling "daisy heads." - The combination of irregular shape and rough texture is a key diagnostic feature. *Staphylococcus aureus* - Typically forms **circular**, **smooth**, **shiny**, and often **golden-yellow colonies** on blood agar. - Colonies are regular in shape with a creamy, opaque appearance—distinctly different from the irregular, rough colonies of *C. diphtheriae*. *Streptococcus pyogenes* - Characteristically produces **small**, **translucent**, **smooth**, **beta-hemolytic colonies** on blood agar. - Colonies are regular, round, and smooth-textured, lacking both the irregular shape and rough texture of *C. diphtheriae*. *Bacillus anthracis* - Forms **large**, **flat**, **gray-white colonies** with a **rough, ground-glass texture** and the distinctive **"Medusa head" appearance** (comma-shaped projections at the colony edge). - While colonies do have a rough texture, they are typically **large and flat with relatively regular circular shape** when young, unlike the characteristically **irregular-shaped** colonies of *C. diphtheriae*. - The "Medusa head" pattern is the most distinctive colonial feature, differentiating it from the irregular, rough colonial morphology of *C. diphtheriae*.

Question 2423: All are non-sporing anaerobes of medical importance except which of the following?

A. Bacteroides
B. Fusobacterium
C. Clostridia (Correct Answer)
D. Actinomyces

Explanation: ***Clostridia*** - This genus is characterized by its ability to form **spores**, which are highly resistant structures allowing survival in adverse conditions. - Examples include *Clostridium difficile*, *Clostridium tetani*, and *Clostridium botulinum*, all of which are important human pathogens. *Actinomyces* - *Actinomyces* are **non-sporing, Gram-positive, anaerobic rods** that cause chronic, granulomatous infections, often forming sinus tracts. - They are known for producing characteristic **"sulfur granules"** in pus. *Bacteroides* - *Bacteroides* are **non-sporing, Gram-negative, anaerobic rods** that are a major component of the normal human gut flora. - They are frequently involved in **intra-abdominal infections** and abscess formation. *Fusobacterium* - *Fusobacterium* species are **non-sporing, Gram-negative, fusiform-shaped anaerobic rods**. - They are common in the **oral cavity** and can cause infections such as Vincent's angina and Lemierre's syndrome.

Question 2424: Pseudomonas is which type of bacteria?

A. Anaerobic
B. Aerobic (Correct Answer)
C. Microaerophilic
D. Obligate anaerobe

Explanation: ***Aerobic*** - **Pseudomonas aeruginosa** is a classic example of an **aerobic bacterium**, meaning it requires oxygen for growth and metabolism. - Its ability to thrive in aerobic environments contributes to its prevalence in hospital settings and its capacity to cause a wide range of infections. *Anaerobic* - Anaerobic bacteria grow in the absence of oxygen and often die in its presence. **Pseudomonas** does not exhibit this characteristic. - Examples of anaerobic bacteria include *Clostridium* species. *Microaerophilic* - Microaerophilic bacteria require oxygen but only in low concentrations (5-10%), higher concentrations are inhibitory. - **Pseudomonas** grows optimally in atmospheric oxygen levels, not restricted to low concentrations. *Obligate anaerobe* - Obligate anaerobes are severely inhibited or killed by oxygen. - This is the opposite of **Pseudomonas**, which strictly requires oxygen for survival.

Question 2425: Which of the following Chlamydia species is primarily associated with respiratory infections?

A. C psittaci
B. C pneumoniae (Correct Answer)
C. C trachomatis
D. None of the options

Explanation: ***C pneumoniae*** - *C. pneumoniae* is the **primary Chlamydia species** associated with **respiratory infections** in humans - It is a common cause of **community-acquired pneumonia** (5-10% of cases), **atypical pneumonia**, **bronchitis**, **pharyngitis**, and **sinusitis** - Transmission occurs via **respiratory droplets** from person to person - Causes both **acute and chronic respiratory infections** and has been linked to exacerbations of asthma and COPD - It is the most frequently encountered Chlamydia species in respiratory tract infections *C psittaci* - Causes **psittacosis** (ornithosis), a specific type of **atypical pneumonia** transmitted from **birds** (parrots, pigeons, poultry) - While it does cause respiratory infection, it is much **less common** than C. pneumoniae and is associated with **occupational or recreational bird exposure** - Not the primary Chlamydia species for general respiratory infections *C trachomatis* - Primarily causes **genital tract infections** (urethritis, cervicitis, PID) and **ocular infections** (trachoma, inclusion conjunctivitis) - Can cause **neonatal pneumonia** in infants exposed during birth, presenting at 1-3 months of age with a staccato cough - NOT a primary respiratory pathogen in adults *None of the options* - This is incorrect because **C. pneumoniae** is definitively the Chlamydia species primarily associated with respiratory infections

Question 2426: 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 2427: 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 2428: Which of the following is an enrichment medium for cholera?

A. TCBS medium
B. Cary-Blair medium
C. Alkaline peptone water (Correct Answer)
D. MacConkey agar

Explanation: ***Alkaline peptone water*** - This is a commonly used **enrichment broth** for *Vibrio cholerae* due to its **high pH (around 8.6)**, which selectively suppresses the growth of most other intestinal flora. - The alkaline environment provides a favorable condition for the rapid multiplication of *Vibrio cholerae* before subculturing onto selective media. *TCBS medium* - **Thiosulfate citrate bile salts sucrose (TCBS) agar** is a **selective and differential medium** used for the isolation of *Vibrio cholerae*, not an enrichment medium. - It differentiates *Vibrio cholerae* (yellow colonies) from most other *Vibrio* species (blue-green colonies) and inhibits the growth of most non-Vibrio bacteria. *Cary-Blair medium* - This is a **transport medium** designed to maintain the viability of enteric bacterial pathogens, including *Vibrio cholerae*, for extended periods at ambient temperatures. - It prevents overgrowth of commensals and helps preserve the pathogen's concentration, but it does not promote growth. *MacConkey agar* - **MacConkey agar** is a **selective and differential medium** primarily used for the isolation and differentiation of gram-negative enteric bacilli. - It is not specifically designed for *Vibrio cholerae* and its selective properties (bile salts and crystal violet) and differential properties (lactose fermentation) are less optimal for *Vibrio* isolation compared to specialized media.

Question 2429: 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 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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