Bacteriology Practice Questions

Q: A patient with a cavitary lung lesion who coughs up sputum containing thin, acid-fast positive rods. Which of the following features would most likely be associated with these bacteria?

Waxy envelope. ***Waxy envelope*** - The presence of a **waxy envelope**, primarily due to high mycolic acid content in the cell wall, is a hallmark of **Mycobacterium tuberculosis**, which causes the described cavitary lung lesion and acid-fast rods. - This waxy layer contributes to the bacterium's **acid-fastness** and resistance to many antibiotics and host defenses. *Nutritional requirement for factors V and X (related to Haemophilus influenzae)* - This describes the growth requirements for **Haemophilus influenzae**, a common cause of respiratory infections but not typically associated with cavitary lung lesions or acid-fast rods. - *Haemophilus influenzae* is a **Gram-negative coccobacillus** and does not exhibit acid-fast staining properties. *Streptokinase (produced by Streptococci)* - **Streptokinase** is an enzyme produced by certain **Streptococcus species** that helps dissolve blood clots. - *Streptococci* are Gram-positive cocci and do not cause cavitary lung lesions with acid-fast rods; they are more commonly associated with pharyngitis, skin infections, and pneumonia (e.g., *Streptococcus pneumoniae*). *Toxic shock syndrome toxin (produced by Staphylococcus aureus)* - **Toxic shock syndrome toxin-1 (TSST-1)** is a superantigen produced by some strains of **Staphylococcus aureus**, leading to toxic shock syndrome. - *Staphylococcus aureus* is a **Gram-positive coccus** that can cause pneumonia and abscesses, but it does not produce acid-fast rods or typically form cavitary lung lesions with the specific characteristics mentioned.

Q: Which of the following is a non-lactose-fermenting bacterium?

Salmonella. ***Salmonella*** - *Salmonella* is a classic example of a **non-lactose-fermenting** bacterium, which differentiates it from many other enteric gram-negative rods on differential media like MacConkey agar. - On MacConkey agar, *Salmonella* colonies typically appear **pale** or **colorless**, lacking the pink-red color indicative of lactose fermentation. *E. coli* - *E. coli* is a **lactose-fermenting** bacterium, producing acid and gas from lactose. - On MacConkey agar, *E. coli* colonies appear **pink to red** due to acid production from lactose fermentation. *Klebsiella* - *Klebsiella* species are also **lactose-fermenting** bacteria, known for their mucoid colonies. - On MacConkey agar, *Klebsiella* colonies are typically **pink** and often very **mucoid**. *Citrobacter* - *Citrobacter* species are generally **lactose-fermenting** bacteria, similar to *E. coli* and *Klebsiella*. - They produce **pink colonies** on MacConkey agar due to acid production from lactose.

Q: Which of the following statements about Helicobacter pylori is false?

Gram positive bacillus. ***Gram positive bacillus*** - *Helicobacter pylori* is a **Gram-negative**, spiral-shaped bacterium, not Gram-positive. - Its Gram-negative cell wall structure is a key characteristic, distinguishing it from Gram-positive organisms. *Urease positive bacillus* - This statement is **true**; *H. pylori* produces large amounts of **urease**, an enzyme that hydrolyzes urea into ammonia and carbon dioxide. - The production of ammonia helps neutralize stomach acid, allowing *H. pylori* to survive in the acidic gastric environment. *Highly associated with duodenal ulcer* - This statement is **true**; *H. pylori* infection is a major cause of both **gastric and duodenal ulcers**. - It is present in over 90% of patients with duodenal ulcers and a significant proportion of those with gastric ulcers. *Resistant to acidic pH of stomach* - This statement is **true**; *H. pylori* has multiple mechanisms to survive in the harsh acidic environment of the stomach. - It produces **urease** to create an alkaline microenvironment and has **flagella** that allow it to burrow into the protective mucus layer.

Q: Which bacteria has amphitrichous flagella?

Campylobacter jejuni. ***Campylobacter jejuni*** - *Campylobacter jejuni* typically exhibits **amphitrichous flagella**, meaning it possesses **single flagellum at both ends** of the bacterial cell. - This arrangement contributes to its characteristic **corkscrew-like motility**, which is important for its pathogenicity and ability to penetrate host mucus. *Spirillum minus* - *Spirillum minus* is known for its **tufts of lophotrichous flagella** at both ends, not a single flagellum at each end. - This bacterium is spiral-shaped and causes rat-bite fever, but its flagellar arrangement is distinct from amphitrichous. *Listeria monocytogenes* - *Listeria monocytogenes* is **peritrichous**, meaning it has flagella distributed all over its cell surface. - While motile, its flagellar arrangement is not amphitrichous; it uses these flagella for movement in the extracellular environment and **actin polymerization** for intracellular movement. *Aquaspirillum serpens* - *Aquaspirillum serpens* is characterized by **polar tufts of lophotrichous flagella**, similar to *Spirillum minus*, and not a single flagellum at each pole. - It is a Gram-negative aquaspirillum, and its flagellar arrangement provides efficient motility in aquatic environments.

Q: Virulence determinant implicated in the pathogenesis of scarlet fever is -

Pyrogenic exotoxin (toxin produced by bacteria). ***Pyrogenic exotoxin (toxin produced by bacteria)*** - Scarlet fever is caused by strains of **_Streptococcus pyogenes_** (Group A Streptococcus, GAS) that produce **streptococcal pyrogenic exotoxins (SPEs)**, also known as erythrogenic toxins. - These toxins act as superantigens, leading to the characteristic **scarlet rash** and other systemic symptoms of scarlet fever. *Hyaluronidase (enzyme aiding tissue invasion)* - **Hyaluronidase** is an enzyme produced by _S. pyogenes_ that degrades hyaluronic acid, a component of connective tissue, facilitating bacterial spread. - While it contributes to the invasiveness of GAS infections, it is **not directly responsible for the characteristic symptoms of scarlet fever**. *M protein (immune evasion factor)* - The **M protein** is a major virulence factor of _S. pyogenes_ that helps the bacteria resist phagocytosis and adhere to host cells. - It plays a critical role in the pathogenesis of various GAS infections but is **not the direct cause of the scarlet rash or systemic toxicity of scarlet fever**. *Streptokinase (enzyme aiding bacterial spread)* - **Streptokinase** is an enzyme produced by _S. pyogenes_ that activates plasminogen, leading to the dissolution of fibrin clots and aiding bacterial spread through tissues. - While important for bacterial dissemination, it is **not the specific virulence factor responsible for the clinical features of scarlet fever**.

Q: Which organism is most commonly associated with the wearing of soft contact lenses?

Pseudomonas aeruginosa. ***Pseudomonas aeruginosa*** - This is the **most common bacterial pathogen** causing contact lens-related microbial keratitis, accounting for 30-50% of cases. - Particularly associated with **soft contact lens wear**, it is known for rapid progression and severe corneal ulceration. - Risk factors include **overnight wear**, poor lens hygiene, and contaminated lens storage cases. - Can lead to **sight-threatening keratitis** within 24-48 hours if untreated. *Acanthamoeba* - While strongly associated with contact lens wear (especially poor hygiene and water exposure), it is **much less common** than bacterial causes. - Acanthamoeba keratitis is a severe protozoal infection but has a relatively low incidence (~1-2 per million contact lens wearers). - Characterized by severe pain disproportionate to clinical signs and ring-shaped stromal infiltrate. *Staphylococcus aureus* - A common cause of bacterial keratitis but **less specifically associated** with soft contact lens wear compared to Pseudomonas. - More commonly causes blepharitis and external eye infections. *Aspergillus* - Fungal keratitis is **rarely associated** with contact lens wear in developed countries. - More commonly linked to ocular trauma with vegetative matter in agricultural settings.

Q: A 24-year-old woman is breastfeeding 3 weeks after giving birth to a normal term infant and notices fissures in the skin around her left nipple. Over the next 3 days, a 5-cm region near the nipple becomes erythematous and tender, with purulent exudate from a small abscess draining through a fissure. Which of the following organisms is most likely to be cultured from the exudate?

Staphylococcus aureus. ***Staphylococcus aureus*** - This presentation of **mastitis with abscess formation** is overwhelmingly caused by **_Staphylococcus aureus_**, especially in breastfeeding women. - The organism gains entry through **nipple fissures**, leading to erythema, tenderness, and purulent exudate characteristic of a bacterial infection. *Candida albicans* - While it can cause **nipple soreness** and **thrush** in infants, it typically presents as burning pain and shiny skin, not usually with a localized abscess and purulent exudate. - *Candida* infections are more common with **antibiotic use** or in women with compromised immune systems. *Lactobacillus acidophilus* - This is a common **probiotic organism** found in the gut and vagina, known for its beneficial role. - It does not cause purulent infections or mastitis in this context. *Listeria monocytogenes* - This bacterium is primarily known for causing **foodborne illness** and can lead to severe infections like meningitis or sepsis, particularly in pregnant women and neonates. - It is not a common cause of superficial abscesses or mastitis in breastfeeding women.

Q: A person developed severe vomiting after eating food from a Chinese restaurant, 3 hours prior. What is the most likely causative agent?

B. cereus. ***B. cereus*** - *Bacillus cereus* produces an **emetic toxin (cereulide)** that causes vomiting within **1-6 hours** after consumption, fitting the 3-hour onset perfectly. - This bacterium is commonly associated with **fried rice** in Chinese restaurants due to improperly cooked or reheated rice where spores survive cooking and germinate. - The preformed heat-stable toxin causes rapid-onset vomiting without significant diarrhea. *Staph. aureus* - While *Staphylococcus aureus* food poisoning also causes rapid-onset vomiting within **1-6 hours** due to preformed enterotoxin, making it a close differential. - However, *B. cereus* is more specifically associated with **starchy foods like rice**, making it the most likely culprit in the context of Chinese restaurant food. *C. difficile* - *Clostridioides difficile* infection primarily causes **diarrhea and pseudomembranous colitis**, typically after antibiotic use disrupting normal gut flora. - The onset of symptoms is typically **days to weeks** after exposure, not acute vomiting within hours of a meal. - Not associated with foodborne transmission. *Pseudomonas* - *Pseudomonas* species rarely cause foodborne illness and are not associated with rapid-onset vomiting. - They are primarily opportunistic pathogens causing infections in immunocompromised individuals or healthcare settings. - When implicated in food contamination, they affect raw produce, not typical Chinese restaurant cooked food.

Q: What is the causative agent of Yaws?

Treponema pertenue. ***Treponema pertenue*** - This spirochete is the **causative agent** of **Yaws**, a chronic disfiguring infectious disease primarily affecting the skin, bones, and joints. - Yaws is typically transmitted through **direct skin-to-skin contact** with infectious lesions in tropical and subtropical regions. *Treponema carateum* - This bacterium is responsible for **Pinta**, another non-venereal treponemal infection. - Pinta primarily causes **skin lesions** characterized by dyschromic patches, but does not involve bone or joint destruction as is seen in Yaws. *Treponema pallidum* - This species has several subspecies, with *Treponema pallidum subspecies pallidum* being the cause of **venereal syphilis**. - While *T. pallidum* is a treponemal infection, its clinical presentation and mode of transmission are distinct from Yaws. *Treponema endemicum* - This subspecies of *Treponema pallidum* is the causative agent of **Bejel** (also known as endemic syphilis). - Like Yaws, Bejel is a non-venereal treponemal infection, but it primarily affects mucosal surfaces and bones, with different clinical characteristics than Yaws.

Question 1

A patient with a cavitary lung lesion who coughs up sputum containing thin, acid-fast positive rods. Which of the following features would most likely be associated with these bacteria?

Accepted Answer

Waxy envelope

Answer

Streptokinase production

Answer

Toxic shock syndrome toxin production

Answer

Nutritional requirement for factors V and X

Question 2

Which of the following is a non-lactose-fermenting bacterium?

Accepted Answer

Salmonella

Answer

E. coli

Answer

Citrobacter

Answer

Klebsiella

Question 3

Which of the following statements about Helicobacter pylori is false?

Accepted Answer

Gram positive bacillus

Answer

Urease positive bacillus

Answer

Highly associated with duodenal ulcer

Answer

Resistant to acidic pH of stomach

Question 4

Which bacteria has amphitrichous flagella?

Accepted Answer

Campylobacter jejuni

Answer

Aquaspirillum serpens

Answer

Spirillum minus

Answer

Listeria monocytogenes

Question 5

Virulence determinant implicated in the pathogenesis of scarlet fever is -

Accepted Answer

Pyrogenic exotoxin (toxin produced by bacteria)

Answer

M protein (immune evasion factor)

Answer

Hyaluronidase (enzyme aiding tissue invasion)

Answer

Streptokinase (enzyme aiding bacterial spread)

Question 6

Which of the following statements about Campylobacter jejuni is correct?

Accepted Answer

Most often occurs several days after consumption of undercooked chicken.

Answer

Gram-positive coccus

Answer

Symptoms may initially mimic appendicitis

Answer

Macrolides should be used in all cases

Question 7

Which organism is most commonly associated with the wearing of soft contact lenses?

Accepted Answer

Pseudomonas aeruginosa

Answer

Acanthamoeba

Answer

Aspergillus

Answer

Staphylococcus aureus

Question 8

A 24-year-old woman is breastfeeding 3 weeks after giving birth to a normal term infant and notices fissures in the skin around her left nipple. Over the next 3 days, a 5-cm region near the nipple becomes erythematous and tender, with purulent exudate from a small abscess draining through a fissure. Which of the following organisms is most likely to be cultured from the exudate?

Accepted Answer

Staphylococcus aureus

Answer

Candida albicans

Answer

Lactobacillus acidophilus

Answer

Listeria monocytogenes

Question 9

A person developed severe vomiting after eating food from a Chinese restaurant, 3 hours prior. What is the most likely causative agent?

Accepted Answer

B. cereus

Answer

C. difficile

Answer

Staph. aureus

Answer

Pseudomonas

Question 10

What is the causative agent of Yaws?

Accepted Answer

Treponema pertenue

Answer

Treponema endemicum

Answer

Treponema pallidum

Answer

Treponema carateum

Bacteriology — MCQs

Bacteriology — MCQs

On this page

Practice by Chapter

Want unlimited practice?