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: 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: Which of the following statements about Mycoplasma is correct?

Mycoplasma pneumoniae can cause lung infections.. ***Mycoplasma pneumoniae can cause lung infections.*** - **_Mycoplasma pneumoniae_** is a well-known cause of **atypical pneumonia**, often referred to as "walking pneumonia." - It infects the respiratory tract, leading to symptoms like **cough**, **fever**, and **sore throat**. - It is one of the most common causes of community-acquired pneumonia, especially in young adults and children. *Penicillin is effective against Mycoplasma.* - **Penicillin** and other beta-lactam antibiotics target bacterial **cell wall synthesis**. - **_Mycoplasma_** species inherently **lack a cell wall**, rendering these antibiotics ineffective. - Treatment requires antibiotics that target other mechanisms like protein synthesis (macrolides, tetracyclines). *Mycoplasma has a thick cell wall.* - **_Mycoplasma_** species are unique among bacteria because they **completely lack a cell wall**, making them pleomorphic (variable in shape). - This absence of a cell wall is a key characteristic that distinguishes them from most other bacteria. - The lack of cell wall makes them resistant to beta-lactam antibiotics and allows them to pass through bacterial filters. *Mycoplasma can be easily cultured on standard blood agar.* - **_Mycoplasma_** species are extremely **fastidious organisms** that require **specialized culture media** such as PPLO (pleuropneumonia-like organism) agar enriched with serum and yeast extract. - They cannot grow on standard blood agar or routine bacterial culture media. - Colonies are very small ("fried egg" appearance) and may take **1-3 weeks** to grow, making culture challenging.

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: 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 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: 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: What is a key distinguishing feature of meningococci compared to gonococci?

Ferment maltose. ***Ferment maltose*** - *Neisseria meningitidis* ferments both **glucose and maltose**, which is a key biochemical characteristic used for its identification. - *Neisseria gonorrhoeae* only ferments **glucose**, differentiating it from meningococci. *Are intracellular pathogens* - Both **meningococci** (*Neisseria meningitidis*) and **gonococci** (*Neisseria gonorrhoeae*) are facultative intracellular pathogens, meaning they can survive and replicate within host cells. - Therefore, this feature does not distinguish between the two. *Are catalase positive* - Both *Neisseria meningitidis* and *Neisseria gonorrhoeae* are **catalase-positive**, meaning they produce the enzyme catalase. - This characteristic is common to both and thus cannot be used to differentiate them. *Possess a capsule* - While *Neisseria meningitidis* possesses a **polysaccharide capsule**, which is a major virulence factor, *Neisseria gonorrhoeae* typically **lacks a capsule**. - However, the ability to ferment maltose is a more direct and commonly used biochemical distinguishing feature in laboratory settings.

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.

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 antibiotic is Actinomycosis sensitive to?

Accepted Answer

Penicillin

Answer

Streptomycin

Answer

Nystatin

Answer

Doxycycline

Question 3

Which of the following statements about Mycoplasma is correct?

Accepted Answer

Mycoplasma pneumoniae can cause lung infections.

Answer

Penicillin is effective against Mycoplasma.

Answer

Mycoplasma has a thick cell wall.

Answer

Mycoplasma can be easily cultured on standard blood agar.

Question 4

How many flagella does Helicobacter pylori typically have?

Accepted Answer

4-6

Answer

3

Answer

2

Answer

1

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 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 7

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 8

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 9

What is a key distinguishing feature of meningococci compared to gonococci?

Accepted Answer

Ferment maltose

Answer

Are intracellular pathogens

Answer

Are catalase positive

Answer

Possess a capsule

Question 10

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

Bacteriology — MCQs

Bacteriology — MCQs

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