Bacteriology Practice Questions

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: Inclusion body containing glycogen is seen in which of the following organisms?

Chlamydia trachomatis. ***Chlamydia trachomatis*** - This species is known to form **intracytoplasmic inclusion bodies** that contain **glycogen**. - The presence of this glycogen allows these inclusions to be stained by **iodine**, aiding in laboratory identification. *Chlamydia pneumoniae* - Inclusion bodies of *Chlamydia pneumoniae* are typically **round or pear-shaped** and **do not contain glycogen**. - They are often **vacuolated** and stain poorly with iodine, unlike those of *C. trachomatis*. *Chlamydia psittaci* - The inclusion bodies of *Chlamydia psittaci* are usually **dense and pleiomorphic**, but they **do not contain glycogen**. - They tend to be **larger** and are often found near the host cell nucleus. *None of the options* - This option is incorrect because *Chlamydia trachomatis* specifically forms **glycogen-containing inclusion bodies**. - The presence of glycogen within inclusions is a key distinguishing feature of this species.

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: What is the most common cause of Hemolytic Uremic Syndrome (HUS) in children?

E. coli O157:H7. ***E. coli O157:H7*** - This **Shiga toxin-producing E. coli (STEC)** strain is the predominant cause of **diarrhea-associated HUS** in children. - The Shiga toxin damages endothelial cells, leading to **thrombotic microangiopathy**, red blood cell fragmentation, and acute kidney injury. - Accounts for approximately **90% of typical HUS cases** in children. *Salmonella typhi* - This bacterium is primarily responsible for causing **typhoid fever**, a systemic illness characterized by prolonged fever, abdominal pain, and sometimes rash. - While it can cause gastrointestinal symptoms, it is **not a cause of HUS**. *Shigella dysenteriae* - This bacterium causes **shigellosis**, an acute inflammatory colitis characterized by bloody diarrhea. - Although *Shigella dysenteriae* type 1 produces **Shiga toxin** and can cause HUS, it is a **less common cause in most developed countries** compared to *E. coli O157:H7*. - More commonly associated with HUS in developing countries with poor sanitation.

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

C pneumoniae. ***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

Q: An adolescent male developed vomiting and diarrhea 1 hour after having food from a restaurant. The most likely pathogen is?

Staphylococcus aureus. ***Staphylococcus aureus*** - The rapid onset of symptoms (within 1 hour) strongly suggests **pre-formed toxin ingestion**, which is characteristic of *Staphylococcus aureus* food poisoning. - While the typical incubation period is **1-6 hours** (average 2-4 hours), onset within 1 hour can occur with **high toxin loads** in contaminated food. - **Vomiting** is often the predominant symptom, occurring shortly after consuming contaminated food, which distinguishes it from other bacterial causes. *Clostridium perfringens* - Onset of symptoms caused by *Clostridium perfringens* is typically **8-16 hours** after ingestion, which is much longer than observed here. - It primarily causes **diarrhea and abdominal cramps** due to toxin production in the intestine, with minimal vomiting. *Vibrio parahaemolyticus* - Symptoms usually appear **4-96 hours** (average 12-24 hours) after consuming contaminated seafood, which is a longer incubation period than described. - It typically causes **watery diarrhea**, abdominal cramps, nausea, and occasional vomiting, but not within 1 hour. *Salmonella* - The incubation period for *Salmonella* infection is typically **6-72 hours** (average 12-36 hours), making it highly unlikely for symptoms to appear within 1 hour. - **Diarrhea, fever, and abdominal cramps** are common with *Salmonella*, but rapid-onset vomiting from pre-formed toxin is not its mechanism.

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 organism is responsible for producing Draughtsman (Concentric Rings) on culture?

Bacillus anthracis. ***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*

Q: Color of granules in mycetoma caused by Actinomadura pelletierrii -

Red. ***Red*** - *Actinomadura pelletierrii* is a common cause of **actinomycetoma** and is characterized by producing **red granules** in the lesions. - The color of these granules is a key diagnostic feature, helping differentiate it from other causes of mycetoma. *Black* - **Black granules** are typically associated with **eumycetoma** caused by **dematiaceous fungi** such as *Madurella mycetomatis*. - This color indicates the presence of **melanin**, a pigment produced by these fungal species. *Yellow* - **Yellow granules** are commonly seen in actinomycetoma caused by organisms such as *Nocardia brasiliensis* or sometimes *Actinomadura madurae*. - This color helps differentiate these specific actinomycetes from other types that produce different granule colors. *Brown* - While varying shades of color can occur, **brown granules** are not the characteristic color produced by *Actinomadura pelletierrii*. - Some *Streptomyces* species or certain eumycetoma agents can occasionally produce brownish granules, but red is specific for *A. pelletierrii*.

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.

Question 1

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 2

Inclusion body containing glycogen is seen in which of the following organisms?

Accepted Answer

Chlamydia trachomatis

Answer

Chlamydia pneumoniae

Answer

Chlamydia psittaci

Answer

None of the options

Question 3

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

Accepted Answer

Campylobacter jejuni

Answer

Bacillus anthracis

Answer

Shigella

Answer

Pneumococcus

Question 4

What is the most common cause of Hemolytic Uremic Syndrome (HUS) in children?

Accepted Answer

E. coli O157:H7

Answer

Salmonella typhi

Answer

Shigella dysenteriae

Question 5

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

Accepted Answer

C pneumoniae

Answer

C psittaci

Answer

C trachomatis

Answer

None of the options

Question 6

An adolescent male developed vomiting and diarrhea 1 hour after having food from a restaurant. The most likely pathogen is?

Accepted Answer

Staphylococcus aureus

Answer

Clostridium perfringens

Answer

Vibrio parahaemolyticus

Answer

Salmonella

Question 7

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 8

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

Accepted Answer

Bacillus anthracis

Answer

B. pertussis

Answer

H. ducreyi

Answer

Pneumococci

Question 9

Color of granules in mycetoma caused by Actinomadura pelletierrii -

Accepted Answer

Red

Answer

Black

Answer

Yellow

Answer

Brown

Question 10

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

Bacteriology — MCQs

Bacteriology — MCQs

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