Bacteriology Practice Questions

Q: Which of the following conditions is caused by Staphylococcus aureus?

Bullous impetigo. ***Bullous impetigo*** - Bullous impetigo is a superficial skin infection characterized by **blisters (bullae)**, and is specifically caused by **Staphylococcus aureus** producing exfoliative toxins. - The toxins produced by *S. aureus* cause intraepidermal cleavage, leading to the formation of the characteristic **flaccid bullae**. *Corynebacterium minutissimum infection* - *Corynebacterium minutissimum* causes **erythrasma**, a chronic superficial skin infection characterized by well-demarcated reddish-brown patches, often in intertriginous areas. - It does not cause bullous impetigo and is typically diagnosed by its coral-red fluorescence under a **Wood's lamp**. *Haemophilus ducreyi infection* - *Haemophilus ducreyi* is the causative agent of **chancroid**, a sexually transmitted infection characterized by painful genital ulcers with a necrotic base and often accompanied by swollen, tender regional lymph nodes. - It is not associated with skin blistering or bullous impetigo. *Propionibacterium acnes infection* - *Propionibacterium acnes* (now *Cutibacterium acnes*) is a bacterium commonly implicated in **acne vulgaris**, contributing to inflammation and comedone formation within hair follicles. - It causes inflammatory lesions like papules, pustules, nodules, and cysts, rather than bullous lesions.

Q: Which of the following organisms is least likely to cause Fournier's gangrene?

Staphylococcus aureus. ***Staphylococcus aureus*** - While *Staphylococcus aureus* can cause various soft tissue infections, it is **less commonly implicated** in the polymicrobial, synergistic infection characteristic of Fournier's gangrene compared to the other listed organisms. - Fournier's gangrene is typically caused by a **synergy of aerobic and anaerobic bacteria**, where *S. aureus* is primarily a notable aerobic pathogen but not a dominant one in the specific context of this necrotizing fasciitis. *Streptococcus pyogenes* - *Streptococcus pyogenes* (Group A Streptococcus) is a well-known cause of **necrotizing fasciitis**, including in the perineal region, often referred to as "flesh-eating bacteria." - It rapidly invades tissues and releases toxins, contributing significantly to the severe tissue destruction seen in Fournier's gangrene. *Bacteroides fragilis* - *Bacteroides fragilis* is a **strict anaerobe** and a common inhabitant of the gut, making it a frequent pathogen in infections originating from the perineum or gastrointestinal tract. - Its presence is highly characteristic of the **polymicrobial nature** of Fournier's gangrene, contributing to the anaerobic environment that promotes tissue necrosis. *Clostridium perfringens* - *Clostridium perfringens* is a **strict anaerobe** notorious for causing **gas gangrene (clostridial myonecrosis)**, a severe form of necrotizing soft tissue infection. - Its ability to produce gas and toxins contributes to rapid tissue destruction and is a significant component of the severe mixed infections seen in Fournier's gangrene.

Q: An 18-year-old girl in an endemic area presents with acute watery diarrhea. Considering the common infectious agents, what is the most likely causative agent?

V. cholerae. ***V. cholerae*** - **Cholera** presents with **acute watery diarrhea**, often described as "rice water stools," which can lead to rapid dehydration. - The patient resides in an **endemic area**, significantly increasing the likelihood of *Vibrio cholerae* infection. *Rotavirus* - While *Rotavirus* causes acute watery diarrhea, it is more common in **infants and young children** (under 5 years old), making it less likely in an 18-year-old. - *Rotavirus* infections are typically seasonal in temperate climates and less tied to endemic area status in adults. *Salmonella* - *Salmonella* infections typically present with **bloody-mucoid diarrhea** (dysentery), fever, and abdominal cramps, rather than purely watery diarrhea. - While *Salmonella* can cause watery diarrhea, the classic presentation often involves more systemic symptoms and an inflammatory response. *Shigella* - *Shigella* infections also typically cause **dysentery**, characterized by **bloody diarrhea**, fever, and tenesmus, due to invasion of the intestinal mucosa. - The absence of blood in the stool and the description of "acute watery diarrhea" make *Shigella* less probable than *V. cholerae*.

Q: Necrotizing fasciitis is caused by -

Beta hemolytic streptococci. ***Beta hemolytic streptococci*** - **Group A Streptococcus (GAS)**, specifically *Streptococcus pyogenes*, is the most common cause of **Type II necrotizing fasciitis**. - Its virulence factors, like **exotoxins**, contribute to rapid tissue destruction and systemic toxicity. *Staphylococcus aureus* - While *S. aureus* can cause severe skin and soft tissue infections, it is more commonly associated with **cellulitis**, **abscesses**, and **septic arthritis**. - It can be a co-pathogen in **polymicrobial (Type I) necrotizing fasciitis** but is less frequent as a sole cause compared to GAS for Type II. *Pneumococcus* - *Streptococcus pneumoniae* (Pneumococcus) is primarily known for causing respiratory infections like **pneumonia**, **otitis media**, and **meningitis**. - It is not a typical causative agent of necrotizing fasciitis. *Clostridium perfringens* - This bacterium is the primary cause of **gas gangrene** (clostridial myonecrosis), a severe form of necrotizing soft tissue infection involving muscle tissue. - While also a flesh-eating bacterium, its clinical presentation and typical affected tissues differ from those of necrotizing fasciitis caused by streptococci.

Q: How many flagella does Helicobacter pylori typically have?

4-6. ***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.

Q: Which antibiotic is Actinomycosis sensitive to?

Penicillin. ***Penicillin*** - **Penicillin** is the **antibiotic of choice** for treating Actinomycosis due to the organism's high sensitivity. - Treatment typically involves a **long course** of high-dose penicillin for several months. *Streptomycin* - **Streptomycin** is an **aminoglycoside antibiotic** primarily used for **tuberculosis** and some gram-negative bacterial infections. - It is **not effective** against Actinomyces species. *Nystatin* - **Nystatin** is an **antifungal medication** used to treat **yeast infections**, particularly Candida. - It has **no antibacterial activity** and thus no role in treating Actinomycosis. *Doxycycline* - While **doxycycline** can be used as an **alternative** in patients allergic to penicillin, it is **not the primary choice**. - Its effectiveness is generally less pronounced than penicillin, and it's reserved for second-line treatment.

Q: Botulism is most commonly due to -

Home-canned vegetables. ***Home-canned vegetables*** - **Home-canned vegetables** are the **most common** source of botulism, particularly improperly processed low-acid vegetables like beans, corn, and asparagus - *Clostridium botulinum* spores survive inadequate heat treatment and germinate in the **anaerobic, low-acid environment** of improperly canned foods - The **lack of sufficient heat sterilization** (pressure canning at 121°C/250°F is required) allows spore survival and subsequent toxin production - Most foodborne botulism outbreaks are traced to **home-canned vegetables** rather than commercially processed foods *Meat* - While improperly preserved meats can cause botulism, they are **not the most common source** in epidemiological data - Commercial meat processing standards and refrigeration significantly reduce this risk - Meat-associated botulism is more common in certain cultural practices involving fermented or preserved meats *Egg* - **Eggs** are not associated with botulism as they do not provide the anaerobic environment necessary for *Clostridium botulinum* toxin production - Eggs are more commonly linked to **Salmonella infections** if improperly handled or undercooked *Milk* - **Milk** and dairy products are not typical sources of botulism - **Pasteurization** and refrigeration prevent conditions favorable for *C. botulinum* growth - Dairy products are more associated with **Listeria** or **Campylobacter** if contaminated

Q: Which of the following statements about B. quintana is false?

Tick is the vector. ***Tick is the vector*** - This statement is **false** because *Bartonella quintana* (B. quintana) is primarily transmitted by the **human body louse**, not ticks. - The disease it causes, **trench fever**, was historically associated with crowded and unsanitary conditions where lice thrive. *Causes trench fever* - *B. quintana* is the causative agent of **trench fever**, a louse-borne illness characterized by recurrent febrile episodes. - This symptom was highly prevalent among soldiers in the trenches during World War I. *Recurrence is common* - **Relapsing fever** (recurrence) is a characteristic feature of trench fever, often occurring several times over weeks or months. - This recurrence is due to the **intracellular survival of *Bartonella* species** within erythrocytes and endothelial cells, making clearance difficult. *Not detected by Weil-Felix reaction* - The **Weil-Felix reaction** is a serological test used to detect certain rickettsial infections, which cross-react with *Proteus* antigens. - *Bartonella quintana* infections **do not typically produce antibodies** that cross-react with *Proteus* antigens; therefore, the Weil-Felix test would not be positive for trench fever.

Q: Which of the following is the mechanism of action of tetanospasmin ?

Inhibition of release of GABA and glycine. ***Inhibition of release of GABA and glycine*** - **Tetanospasmin** is a potent neurotoxin produced by *Clostridium tetani* that acts by blocking the release of inhibitory neurotransmitters, specifically **GABA (gamma-aminobutyric acid)** and **glycine**, from presynaptic terminals in the spinal cord and brainstem. - This inhibition leads to **uncontrolled muscle spasms**, rigidity, and convulsions, characteristic of tetanus, due to the lack of inhibitory signals to motor neurons. *Inhibition of Ach release from synapse* - This mechanism is characteristic of **botulinum toxin** (produced by *Clostridium botulinum*), not tetanospasmin. - Botulinum toxin inhibits the release of **acetylcholine (ACh)** at the neuromuscular junction, leading to flaccid paralysis. *Inhibition of protein synthesis* - This mechanism is associated with toxins like **diphtheria toxin** and **exotoxin A** from *Pseudomonas aeruginosa*. - These toxins inactivate elongation factor-2 (EF-2), thereby blocking protein synthesis and causing cell death. *Activation of adenylyl cyclase* - Toxins such as **cholera toxin** and **pertussis toxin** act by activating adenylyl cyclase, leading to an increase in intracellular cAMP levels. - This mechanism causes effects like severe diarrhea in cholera and respiratory symptoms in whooping cough.

Question 1

Which of the following conditions is caused by Staphylococcus aureus?

Accepted Answer

Bullous impetigo

Answer

Corynebacterium minutissimum infection

Answer

Haemophilus ducreyi infection

Answer

Propionibacterium acnes infection

Question 2

Which of the following organisms is least likely to cause Fournier's gangrene?

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus pyogenes

Answer

Bacteroides fragilis

Answer

Clostridium perfringens

Question 3

An 18-year-old girl in an endemic area presents with acute watery diarrhea. Considering the common infectious agents, what is the most likely causative agent?

Accepted Answer

V. cholerae

Answer

Rotavirus

Answer

Salmonella

Answer

Shigella

Question 4

Which of the following statements about Haemophilus influenzae is true?

Accepted Answer

Encapsulated strains are the most common cause of severe H. influenzae diseases

Answer

It is not capsulated

Answer

Invasive strain causes severe diseases but is less common than non-invasive strains

Answer

Typically grown on chocolate agar in CO2-enriched environment but not clinically relevant to severe diseases

Question 5

Necrotizing fasciitis is caused by -

Accepted Answer

Beta hemolytic streptococci

Answer

Pneumococcus

Answer

Staphylococcus aureus

Answer

Clostridium perfringens

Question 6

How many flagella does Helicobacter pylori typically have?

Accepted Answer

4-6

Answer

3

Answer

2

Answer

1

Question 7

Which antibiotic is Actinomycosis sensitive to?

Accepted Answer

Penicillin

Answer

Streptomycin

Answer

Nystatin

Answer

Doxycycline

Question 8

Botulism is most commonly due to -

Accepted Answer

Home-canned vegetables

Answer

Egg

Answer

Milk

Answer

Meat

Question 9

Which of the following statements about B. quintana is false?

Accepted Answer

Tick is the vector

Answer

Recurrence is common

Answer

Causes trench fever

Answer

Not detected by Weil-Felix reaction

Question 10

Which of the following is the mechanism of action of tetanospasmin ?

Accepted Answer

Inhibition of release of GABA and glycine

Answer

Inhibition of Ach release from synapse

Answer

Inhibition of protein synthesis

Answer

Activation of adenylyl cyclase

Bacteriology — MCQs

Bacteriology — MCQs

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