Bacteriology Practice Questions

Q: Which of the following statements about Chlamydia is false?

Gram positive. ***Gram positive*** - Chlamydia are **Gram-negative** bacteria, despite their unique cell wall structure which lacks a peptidoglycan layer but contains an outer membrane with lipopolysaccharide (LPS) [1]. - The statement that Chlamydia are Gram positive is therefore **FALSE**, making this the correct answer. *Obligate intracellular organism* - This statement is TRUE. Chlamydia are indeed **obligate intracellular organisms**, meaning they can only replicate inside host cells [2]. - They rely on the host cell for ATP and other metabolic precursors, earning them the nickname "energy parasites" [2]. *Reticulate body is metabolically active* - This statement is TRUE. The **reticulate body (RB)** is the metabolically active and replicative form of Chlamydia that resides within the host cell [1]. - It undergoes binary fission to produce more RBs before differentiating back into elementary bodies [1]. *Replicate by binary fission* - This statement is TRUE. The **reticulate bodies** of Chlamydia replicate primarily through **binary fission** within the inclusion bodies inside the host cell cytoplasm [1]. - This process allows for the rapid amplification of the bacteria.

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 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.

Q: A child presents with fever, abdominal cramps, and bloody stools. Which organism is the most likely cause?

EHEC. ***EHEC*** - **Enterohemorrhagic *E. coli*** (EHEC), particularly O157:H7, is well-known for causing **bloody diarrhea** and severe abdominal cramps, especially in children, due to the production of **Shiga toxins**. - Shiga toxins can lead to **hemolytic uremic syndrome (HUS)**, a serious complication characterized by acute kidney failure, hemolytic anemia, and thrombocytopenia. *ETEC* - **Enterotoxigenic *E. coli*** (ETEC) is a common cause of **traveler's diarrhea** and typically presents with **watery diarrhea**, abdominal cramps, and low-grade fever. - It primarily invades the small intestine and produces toxins that promote fluid and electrolyte secretion, but it does **not typically cause bloody stools**. *EPEC* - **Enteropathogenic *E. coli*** (EPEC) typically causes **watery diarrhea** in infants and young children by disrupting the intestinal microvilli, leading to malabsorption. - It does **not produce Shiga toxins** and is generally associated with non-bloody, watery stools and vomiting. *EAEC* - **Enteroaggregative *E. coli*** (EAEC) is associated with persistent diarrhea, especially in children and immunocompromised individuals, due to its ability to adhere to intestinal cells in an aggregative manner. - While it can cause **secretory, watery diarrhea**, it is rarely associated with bloody stools.

Q: Which atypical mycobacteria are known for pigment production?

M. gordonae, M. szulgai. **Correct: M. gordonae, M. szulgai** - **M. gordonae** is a classic **scotochromogen**, producing yellow-orange pigment in both light and dark conditions - **M. szulgai** is unique as it shows **dual chromogenicity**: photochromogen at 25°C and scotochromogen at 37°C - These are the classic examples of **pigment-producing atypical mycobacteria** used for classification purposes - Pigment production (Runyon classification) is a key characteristic differentiating atypical mycobacteria from *M. tuberculosis* *Incorrect: M. fortuitum, M. chelonae* - These are **rapid growers** (Runyon Group IV) and are typically **non-chromogens** - Not primarily known or highlighted for pigment production as a defining feature - Clinically important for causing **skin and soft tissue infections**, especially in post-traumatic or post-surgical settings *Incorrect: M. xenopi, Mycobacterium avium complex (MAC)* - **M. xenopi** is a **non-chromogen** (no pigment production) and is thermophilic - **MAC** (*M. avium* and *M. intracellulare*) are also **non-chromogens** - MAC is an important cause of disseminated disease in immunocompromised patients (especially AIDS) and pulmonary disease in patients with pre-existing lung disease *Incorrect: M. ulcerans (non-pigment producing)* - Correctly identified as a **non-chromogen** (no pigment production) - Causes **Buruli ulcer**, a severe necrotizing skin disease - Distinguished by production of **mycolactone toxin**, not pigment characteristics

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: What is the most common bacterial cause of multiple sinus tracts resulting from an infection of the great toe?

Actinomyces. ***Actinomyces*** - **Actinomycosis** is known for causing **chronic suppurative infections** with **multiple draining sinus tracts** and characteristic **sulfur granules**. - The causative organism is **Actinomyces israelii**, an anaerobic, gram-positive, filamentous bacterium. - While rare, it can affect bones, leading to **osteomyelitis**, especially in the feet, presenting with these multifocal sinus tracts. *Tuberculosis* - **Tuberculosis of bone** is typically a **monoarticular affection**, often affecting larger joints, and does not commonly present with multiple draining sinus tracts like actinomycosis. - It is more common in the spine (**Pott's disease**) and large weight-bearing joints, rather than solely the great toe with multiple sinuses. *Staphylococcus aureus* - **Staphylococcus aureus** is the most common cause of **acute osteomyelitis** and can lead to draining sinuses. - However, it typically causes **single or localized sinus tracts** rather than the extensive, multiple sinus formation associated with actinomycosis. *Pseudomonas aeruginosa* - **Pseudomonas aeruginosa** is often associated with **osteomyelitis following puncture wounds** through footwear. - While it can cause chronic infections, it is not primarily known for forming the characteristic **multiple, long-standing sinus tracts** seen with Actinomyces.

Q: What is the primary virulence factor of Neisseria gonorrhoeae?

Pili (fimbriae). ***Pili (fimbriae)*** - **Pili are the PRIMARY virulence factor** of *Neisseria gonorrhoeae*, essential for **initial attachment and colonization** of urogenital mucosa - Enable bacteria to **adhere to non-ciliated epithelial cells**, resisting mechanical clearance by urination and secretions - Undergo **antigenic variation** to evade host immune responses - Without pili, *N. gonorrhoeae* cannot establish infection *Endotoxin (lipooligosaccharide)* - *N. gonorrhoeae* possesses **LOS (lipooligosaccharide)** which causes inflammation and tissue damage - While important for pathogenesis, it is a **secondary virulence factor** - LOS contributes to symptoms but cannot cause infection without prior colonization via pili *Exotoxin* - *N. gonorrhoeae* does **not produce significant exotoxins** - Pathogenicity is mediated through **adherence factors (pili), LOS, and surface proteins** rather than secreted protein toxins - This is not a mechanism of gonococcal virulence *All of the above are incorrect* - This statement is false as **pili (fimbriae)** are definitively the primary virulence factor for *N. gonorrhoeae*

Q: Which is the PRIMARY hemolysin of Streptococcus pyogenes?

Streptolysin S. ***Streptolysin S*** - This is the **PRIMARY hemolysin** of *Streptococcus pyogenes*, responsible for the characteristic **beta-hemolysis** visible on blood agar plates. - It is **oxygen-stable** and **non-immunogenic**, causing the surface hemolysis that defines Group A Streptococcus phenotypically. *Hyaluronidase* - This enzyme breaks down **hyaluronic acid**, a component of the extracellular matrix in host tissues. - It facilitates **bacterial spread through tissues** but is **not a hemolysin** and does not directly lyse red blood cells. *Streptolysin O* - This is a **thiol-activated cytolysin** that is **oxygen-labile** and primarily important for its **immunogenic properties**. - While it can cause hemolysis, its main clinical significance lies in the **anti-streptolysin O (ASO) titer** used for diagnosing recent infections. *Streptodornase* - Also known as **DNase**, this enzyme digests **DNA**, reducing the viscosity of pus and facilitating bacterial dissemination. - It is **not a hemolysin** but serves as an important virulence factor for tissue invasion.

Question 1

Which of the following statements about Chlamydia is false?

Accepted Answer

Gram positive

Answer

Reticulate body is metabolically active

Answer

Replicate by binary fission

Answer

Obligate intracellular organism

Question 2

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 3

How many flagella does Helicobacter pylori typically have?

Accepted Answer

4-6

Answer

3

Answer

2

Answer

1

Question 4

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

Question 5

A child presents with fever, abdominal cramps, and bloody stools. Which organism is the most likely cause?

Accepted Answer

EHEC

Answer

ETEC

Answer

EAEC

Answer

EPEC

Question 6

Which atypical mycobacteria are known for pigment production?

Accepted Answer

M. gordonae, M. szulgai

Answer

M. fortuitum, M. chelonae

Answer

M. xenopi, Mycobacterium avium complex (MAC)

Answer

M. ulcerans (non-pigment producing)

Question 7

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 8

What is the most common bacterial cause of multiple sinus tracts resulting from an infection of the great toe?

Accepted Answer

Actinomyces

Answer

Tuberculosis

Answer

Pseudomonas aeruginosa

Answer

Staphylococcus aureus

Question 9

What is the primary virulence factor of Neisseria gonorrhoeae?

Accepted Answer

Pili (fimbriae)

Answer

All of the above are incorrect

Answer

Endotoxin (lipooligosaccharide)

Answer

Exotoxin

Question 10

Which is the PRIMARY hemolysin of Streptococcus pyogenes?

Accepted Answer

Streptolysin S

Answer

Hyaluronidase

Answer

Streptodornase

Answer

Streptolysin O

Bacteriology — MCQs

Bacteriology — MCQs

On this page

Practice by Chapter

Want unlimited practice?