Bacteriology Practice Questions

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

Bacillus. ***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.

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

Campylobacter jejuni. ***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.

Q: Which of the following is a saccharolytic species of Clostridium?

Clostridium septicum. ***Clostridium septicum*** - *Clostridium septicum* is a **saccharolytic** species, meaning it ferments carbohydrates to produce gas, which contributes to the rapid tissue destruction seen in **gas gangrene**. - Its ability to rapidly consume sugars in tissues fuels its invasive growth and toxin production, which is characteristic of its pathogenic mechanism. *Clostridium tetani* - *Clostridium tetani* is a **proteolytic** species, primarily deriving its energy from **protein degradation**. - It does not ferment carbohydrates, and its pathogenicity is mainly due to the production of **tetanospasmin**, a neurotoxin. *Clostridium cochlearium* - *Clostridium cochlearium* is a **proteolytic** species that metabolizes proteins and amino acids. - It is not known for significant saccharolytic activity and is typically found in environments rich in protein. *None of the options* - This option is incorrect because *Clostridium septicum* is indeed a saccharolytic species, as detailed above.

Q: Who discovered the bacterium Mycobacterium tuberculosis, which causes tuberculosis?

Robert Koch. ***Robert Koch*** - **Robert Koch** discovered the bacterium *Mycobacterium tuberculosis* in **1882**, identifying its role as the causative agent of tuberculosis. - His work was crucial in establishing the germ theory of disease and earned him the Nobel Prize in Physiology or Medicine in 1905. *Louis Pasteur* - **Louis Pasteur** was a pioneer in microbiology, known for his work on **pasteurization**, **vaccinations** (e.g., rabies and anthrax), and disproving spontaneous generation. - While he made significant contributions to understanding infectious diseases, he did not discover *Mycobacterium tuberculosis*. *Lister* - **Joseph Lister** was a British surgeon who revolutionized surgery by introducing **antiseptic techniques** using carbolic acid to prevent infections. - His contributions were fundamental to reducing mortality rates from surgical infections, but he did not discover the tuberculosis bacterium. *Jenner* - **Edward Jenner** is famous for developing the **smallpox vaccine**, which was a groundbreaking achievement in immunology and public health. - His work, though vital for preventing infectious diseases, predates and is unrelated to the discovery of *Mycobacterium tuberculosis*.

Q: Which of the following stimulate adenylate cyclase with G-protein coupled action ?

Cholera toxin. ***Cholera toxin*** - Cholera toxin is a **G-protein-activating toxin** that irreversibly activates **adenylate cyclase**. - This leads to increased intracellular levels of **cAMP**, causing excessive fluid secretion into the intestinal lumen and severe diarrhea. *Shiga toxin* - Shiga toxin acts by inactivating the **60S ribosomal subunit**, thereby inhibiting protein synthesis in eukaryotic cells. - Its primary effect is **cytotoxicity**, not direct stimulation of adenylate cyclase. *Diphtheria toxin* - Diphtheria toxin inhibits **protein synthesis** by inactivating **elongation factor-2 (EF-2)** through ADP-ribosylation. - This toxin specifically targets host cells, leading to cellular death and tissue damage. *Pseudomonas toxin* - **Exotoxin A** produced by *Pseudomonas aeruginosa* also inhibits **protein synthesis** by ADP-ribosylating and inactivating **EF-2**, similar to diphtheria toxin. - It does not directly affect adenylate cyclase activity.

Q: Which of the following bacteria is known to exhibit antigenic variation?

Borrelia. ***Borrelia*** - *Borrelia* species, particularly *Borrelia burgdorferi* (causing **Lyme disease**), are known for extensive **antigenic variation** of their outer surface proteins (Osps), especially OspC. - This variation helps the bacteria evade the host's immune response, contributing to persistent infection. *Yersinia* - While *Yersinia* species produce various virulence factors, including proteins that interfere with immune cell function, they are not primarily known for the type of rapid and extensive **antigenic variation**seen in *Borrelia*. - Their immune evasion strategies often involve modifying host cell signaling pathways and resisting phagocytosis. *Bordetella* - *Bordetella pertussis*, causative agent of **whooping cough**, varies its expression of adhesins and toxins through **phase variation**, which is a form of phenotypic switching. - However, this is distinct from the frequent and sequential changes in surface antigens (antigenic variation) observed in *Borrelia*. *Brucella* - *Brucella* species are **intracellular pathogens** that primarily evade the immune system by surviving and replicating within host cells. - They do not typically engage in significant **antigenic variation** of their surface components as a primary immune evasion mechanism.

Q: Which is the most common bacterial organism causing bacterial upper respiratory tract infections (including sinusitis, otitis media, and pharyngitis) in adults?

Streptococcus pneumoniae. ***Streptococcus pneumoniae*** - *Streptococcus pneumoniae* is the **most common bacterial pathogen** causing upper respiratory tract infections overall, including **bacterial sinusitis**, **otitis media**, and **community-acquired pneumonia**. - It is a frequent colonizer of the nasopharynx and leads to infection when host immunity is compromised. - Accounts for the highest burden of bacterial URTIs when considering all anatomical sites. *Haemophilus influenzae* - *Haemophilus influenzae* (particularly non-typeable strains) is the **second most common** cause of bacterial sinusitis and otitis media in adults. - While significant, it is less prevalent overall than *S. pneumoniae* across all URTI types. *Staphylococcus aureus* - *Staphylococcus aureus* primarily causes **skin and soft tissue infections** and device-related infections. - It is **not a common primary pathogen** in typical acute bacterial URTIs, though it may cause secondary infections or colonize the anterior nares. *Streptococcus pyogenes* - *Streptococcus pyogenes* (Group A Streptococcus) is the **most common cause of bacterial pharyngitis** (strep throat) in adults. - However, when considering the **full spectrum of bacterial URTIs** (pharyngitis, sinusitis, otitis media), *S. pneumoniae* has a broader overall impact and higher prevalence across multiple sites.

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

Toxin mediated by chromosomal gene. ***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.

Q: Which of the following bacteria is not capsulated?

Proteus. ***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.

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

Corynebacterium diphtheriae. ***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 1

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

Accepted Answer

Bacillus

Answer

Salmonella

Answer

Proteus

Answer

Klebsiella

Question 2

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

Accepted Answer

Campylobacter jejuni

Answer

Bacillus anthracis

Answer

Shigella

Answer

Pneumococcus

Question 3

Which of the following is a saccharolytic species of Clostridium?

Accepted Answer

Clostridium septicum

Answer

Clostridium tetani

Answer

Clostridium cochlearium

Answer

None of the options

Question 4

Who discovered the bacterium Mycobacterium tuberculosis, which causes tuberculosis?

Accepted Answer

Robert Koch

Answer

Jenner

Answer

Louis Pasteur

Answer

Lister

Question 5

Which of the following stimulate adenylate cyclase with G-protein coupled action ?

Accepted Answer

Cholera toxin

Answer

Shiga toxin

Answer

Diphtheria toxin

Answer

Pseudomonas toxin

Question 6

Which of the following bacteria is known to exhibit antigenic variation?

Accepted Answer

Borrelia

Answer

Yersinia

Answer

Bordetella

Answer

Brucella

Question 7

Which is the most common bacterial organism causing bacterial upper respiratory tract infections (including sinusitis, otitis media, and pharyngitis) in adults?

Accepted Answer

Streptococcus pneumoniae

Answer

Staphylococcus aureus

Answer

Haemophilus influenzae

Answer

Streptococcus pyogenes

Question 8

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

Accepted Answer

Toxin mediated by chromosomal gene

Answer

Has metachromatic granules

Answer

Toxigenicity demonstrated by elek's test

Answer

Does not invade deeper tissues

Question 9

Which of the following bacteria is not capsulated?

Accepted Answer

Proteus

Answer

Pneumococcus

Answer

Klebsiella

Answer

Meningococcus

Question 10

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

Accepted Answer

Corynebacterium diphtheriae

Answer

Streptococcus pyogenes

Answer

Bacillus anthracis

Answer

Staphylococcus aureus

Bacteriology — MCQs

Bacteriology — MCQs

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