Bacteriology Practice Questions

Q: In a clinical scenario where a patient presents with flaccid paralysis, which of the following toxins is most likely responsible?

Botulism. ***Correct Option: Botulism*** - **Botulinum toxin** blocks the release of **acetylcholine** at the neuromuscular junction, leading to **flaccid paralysis**. - This paralysis typically progresses symmetrically and can affect ocular, bulbar, and peripheral muscles. *Incorrect Option: Tetanus* - **Tetanus toxin** inhibits the release of **inhibitory neurotransmitters** (**GABA** and **glycine**) in the central nervous system. - This leads to uncontrolled muscle contractions, presenting as **spastic paralysis** and **lockjaw**. *Incorrect Option: Diphtheria* - **Diphtheria toxin** causes local inflammation and can lead to systemic effects, including **myocarditis** and **neuropathy**. - The neuropathy can cause weakness, but it is typically a **delayed polyneuropathy** rather than acute flaccid paralysis. *Incorrect Option: Cholera* - **Cholera toxin** activates adenylyl cyclase in intestinal cells, leading to excessive fluid and electrolyte secretion. - The primary symptom is **severe watery diarrhea** and dehydration, not paralysis.

Q: Blood culture is positive in which infection caused by Staphylococcus aureus?

Infective endocarditis. ***Infective endocarditis*** - **Infective endocarditis** is characterized by the presence of bacteria in the bloodstream, leading to a **positive blood culture** [2]. *Staphylococcus aureus* is a common cause, particularly in intravenous drug users [1], [2]. - The infection involves the **endothelial lining of the heart**, often affecting heart valves, causing vegetations that can shed bacteria into the circulation [2], [3]. *Toxic Shock Syndrome (TSS)* - TSS is caused by toxins (e.g., **TSST-1**) produced by *Staphylococcus aureus*, not by the direct presence of bacteria in the bloodstream in high numbers that would consistently yield a positive blood culture. - While *S. aureus* is present, the systemic effects are primarily **toxin-mediated**, and blood cultures are often negative. *Impetigo* - Impetigo is a **superficial skin infection** caused by *Staphylococcus aureus* or *Streptococcus pyogenes*. - It does not involve systemic bacteremia, so **blood cultures are typically negative**. *Staphylococcal Scalded Skin Syndrome (SSSS)* - SSSS is a **toxin-mediated disease** caused by exfoliatin toxins produced by *Staphylococcus aureus*. - The bacteria usually remain localized at the site of infection (e.g., nose, throat, or skin), and **blood cultures are generally negative**.

Q: Which of the following statements about Enterohemorrhagic E. coli (EHEC) is false?

Sereny test is positive. ***Sereny test is positive*** - The **Sereny test** assesses the invasiveness of bacteria by observing their ability to invade and replicate in epithelial cells, typically in guinea pig conjunctiva. - *Enterohemorrhagic E. coli* (**EHEC**) is **non-invasive**; its pathogenicity stems from its production of **Shiga-like toxins**, not from cellular invasion, making a positive Sereny test statement false. *Commonly causes HUS* - **EHEC**, particularly serotype **O157:H7**, is a well-known cause of **Hemolytic Uremic Syndrome (HUS)**, especially in children and the elderly. - The **Shiga-like toxins** produced by EHEC are absorbed into the bloodstream, damaging endothelial cells and leading to the characteristic triad of **hemolytic anemia**, **thrombocytopenia**, and **acute kidney injury** seen in HUS. *Bloody diarrhea and HUS linked to O157:H7* - **EHEC O157:H7** is the most common serotype associated with outbreaks of **bloody diarrhea** and the subsequent development of **HUS**. - The toxins cause widespread damage to the intestinal lining, leading to **hemorrhagic colitis** (bloody diarrhea), and can then disseminate to distant organs like the kidneys, causing HUS. *Produces Shiga-like toxin* - The primary virulence factor of **EHEC** is the production of **Shiga-like toxins** (also known as **verotoxins**), specifically Stx1 and Stx2. - These toxins inhibit protein synthesis in eukaryotic cells, leading to cell death and tissue damage, which contribute to the severe gastrointestinal symptoms and systemic complications like HUS.

Q: Which of the following is more frequently associated with Klebsiella pneumoniae than with Pseudomonas aeruginosa?

Upper lobe cavitation. Upper lobe cavitation - **Upper lobe cavitation** is a characteristic feature of pneumonia caused by **Klebsiella pneumoniae**, particularly in chronic alcoholics or individuals with poor host defenses [1]. - While *Pseudomonas aeruginosa* can cause severe pneumonia, **cavitary lesions** are less frequently reported and typically occur in immunocompromised patients. *Artificial ventilation* - **Artificial ventilation** is a significant risk factor for nosocomial pneumonia caused by both *Klebsiella pneumoniae* and *Pseudomonas aeruginosa*. - However, the question asks for a feature *more frequently associated* with *Klebsiella pneumoniae*, and ventilation is a common risk for both. *Cystic fibrosis* - **Cystic fibrosis** is overwhelmingly associated with chronic *Pseudomonas aeruginosa* infections, which establish persistent biofilms in the respiratory tract. - While *Klebsiella pneumoniae* can colonize CF patients, it is not the primary or most frequent pathogen linked to this condition. *Diabetes mellitus* - **Diabetes mellitus** increases susceptibility to various infections, including those caused by *Klebsiella pneumoniae* and *Pseudomonas aeruginosa*. - However, it is an underlying condition and not a specific clinical characteristic of the pneumonia itself that differentiates the two organisms.

Q: Atrophic dry nasal mucosa, extensive encrustations, and a woody hard external nose are most suggestive of:

Klebsiella pneumoniae. ***Klebsiella pneumoniae*** - This constellation of symptoms—**atrophic dry nasal mucosa**, **extensive encrustations**, and a **woody hard external nose**—is characteristic of **primary atrophic rhinitis (ozena)** caused by *Klebsiella pneumoniae* subspecies *ozaenae*. - **Ozena** presents with the classic triad of **progressive nasal mucosal atrophy**, **foul-smelling greenish crusts**, and **anosmia** due to destruction of olfactory epithelium. - The **woody hard external nose** suggests either advanced ozena with fibrosis or **rhinoscleroma** (caused by *Klebsiella rhinoscleromatis*), both of which are Klebsiella-related chronic granulomatous conditions. - *K. pneumoniae* subspecies *ozaenae* is the **classic etiological agent** for this severe destructive form of atrophic rhinitis. *Staphylococcus aureus* - *S. aureus* causes **rhinitis sicca anterior** (anterior nasal vestibulitis), characterized by crusting and inflammation **limited to the anterior nasal vestibule**. - Unlike ozena, S. aureus infection does **not cause progressive atrophy** of the entire nasal mucosa or the extensive encrustations throughout the nasal cavity described here. - The **woody hard external nose** is not a feature of staphylococcal nasal infections, which remain superficial. *Peptostreptococcus* - **Peptostreptococcus** species are anaerobic bacteria typically involved in **polymicrobial infections** such as chronic sinusitis, dental abscesses, or deep neck space infections. - They are **not primary pathogens** in chronic atrophic rhinitis and do not cause the specific progressive nasal atrophy and external nasal changes described. *Bacteroides* - **Bacteroides** species are obligate anaerobes that are part of the normal gut flora and commonly cause **intra-abdominal infections** and abscesses. - They are **not associated** with chronic rhinitis, nasal mucosal atrophy, or the external nasal deformities characteristic of ozena or rhinoscleroma.

Q: Which of the following is the MOST CHARACTERISTIC feature of Campylobacter?

Comma-shaped. ***Comma-shaped*** - **Campylobacter** species are classically described as **comma-shaped** or S-shaped (seagull-shaped) **gram-negative rods** when viewed under a microscope. - This distinctive curved morphology is the **most characteristic feature** used in their identification. - The characteristic "darting motility" combined with this morphology makes identification straightforward. *Encapsulated* - **Campylobacter** species are generally **not encapsulated**, differentiating them from other pathogenic bacteria like *Streptococcus pneumoniae*. - Encapsulation is a **virulence factor** that helps bacteria evade phagocytosis but is not typical for **Campylobacter**. *Non-motile* - **Campylobacter** species are **highly motile**, possessing a **single polar flagellum** at one or both ends. - Their characteristic **darting motility** contributes to pathogenicity and ability to penetrate the intestinal mucus layer. - This motility is a crucial feature allowing movement through viscous environments. *Spore-forming* - **Campylobacter** species are **non-spore-forming** bacteria. - Spore formation is characteristic of certain gram-positive bacteria like *Bacillus* and *Clostridium* species. - This helps differentiate Campylobacter from spore-forming enteric pathogens.

Q: Which of the following is a true statement regarding Enterobacteriaceae?

All members are oxidase negative. ***All members are oxidase negative*** - This is the **definitive and universally true** statement for all Enterobacteriaceae, with **no exceptions**. - The **negative oxidase test** is a key defining characteristic that distinguishes Enterobacteriaceae from other Gram-negative bacteria such as *Pseudomonas*. - This enzymatic characteristic is crucial for basic laboratory identification and is **consistently used as a primary screening test** for this family. *Glucose is fermented by most members of the family* - While the fermentation of glucose is indeed a characteristic of Enterobacteriaceae, the statement is **imprecise** because it says "most" when in fact **ALL members** ferment glucose. - The use of "most" makes this statement technically less accurate than the oxidase-negative statement, which correctly uses "all." *Motility in Enterobacteriaceae is via peritrichous flagella* - This statement is **incomplete and potentially misleading** because **not all members are motile**. - While motile members do have **peritrichous flagella** (distributed over the entire cell surface), important members like *Klebsiella* species are **non-motile**. - The statement implies universal motility, which is incorrect. *Nitrate reduction positive* - While all Enterobacteriaceae do reduce nitrates to nitrites, this statement **lacks specificity** compared to the oxidase test. - The oxidase-negative characteristic is more **diagnostically distinctive** and is the **primary screening test** used to differentiate Enterobacteriaceae from other Gram-negative bacteria. - Nitrate reduction is confirmatory but not as definitive for initial identification.

Q: A 26-year-old male patient presented with a granulomatous penile ulcer. On Wright Giemsa staining, tiny organisms of 2 microns are seen engulfed by macrophages. What is the causative organism?

Donovanosis (Calymmatobacterium granulomatis). ***Donovanosis (Calymmatobacterium granulomatis)*** - The presence of **granulomatous penile ulcers** and characteristic **Donovan bodies** (2-micron organisms engulfed by macrophages on Wright-Giemsa stain) are pathognomonic for donovanosis. - This condition is caused by *Calymmatobacterium granulomatis* (now reclassified as *Klebsiella granulomatis*). *Lymphogranuloma venereum (LGV)* - While LGV also causes genital ulcers and lymphadenopathy, the causative agent is *Chlamydia trachomatis* serovars L1, L2, or L3, and it does not present with **Donovan bodies** in macrophages. - Histologically, LGV often shows **stellate abscesses** in lymph nodes, not intracellular organisms in a granulomatous ulcer. *Gonorrhea (Neisseria gonorrhoeae)* - Gonorrhea typically presents as **urethritis** with purulent discharge in males or cervicitis in females, not commonly as a granulomatous penile ulcer. - Microscopic examination would show **Gram-negative intracellular diplococci** within neutrophils, not macrophage-engulfed organisms like Donovan bodies. *Syphilis (Treponema pallidum)* - Primary syphilis manifests as a **painless chancre**, which is typically a clean-based, indurated ulcer, not usually granulomatous. - Diagnosis is made by **darkfield microscopy** to visualize spirochetes or serological tests (e.g., RPR, VDRL, FTA-ABS), not by finding intracellular organisms on Wright-Giemsa stain.

Q: Which of the following organisms is an obligate intracellular bacterium that commonly causes sexually transmitted infections?

Chlamydia. ***Chlamydia*** - **Chlamydia trachomatis** is a classic example of an **obligate intracellular bacterium** that is a leading cause of sexually transmitted infections (STIs). - It has a unique biphasic developmental cycle, alternating between an infectious **elementary body** and a replicative **reticulate body** within host cells. *Rickettsia* - **Rickettsia** species are also **obligate intracellular bacteria** but are primarily transmitted via **arthropod vectors** (e.g., ticks, fleas, lice), causing diseases like **Rocky Mountain spotted fever** and **typhus**. - They are not typically associated with **sexually transmitted infections** in humans. *Mycoplasma* - **Mycoplasma** species are bacteria characterized by the **absence of a cell wall**, but they are generally **extracellular** or **intracellular but not obligate**. - While some *Mycoplasma* species can cause STIs (e.g., *Mycoplasma genitalium*), they do not fit the description of an **obligate intracellular bacterium** in the same way *Chlamydia* does (which requires host cell machinery for energy production). *Prion* - A **prion** is an **infectious protein particle** that lacks genetic material (DNA or RNA) and causes transmissible spongiform encephalopathies (TSEs), such as **Creutzfeldt-Jakob disease**. - It is not a bacterium and is not associated with **sexually transmitted infections**.

Q: Causative agent of trench fever is which of the following?

Bartonella quintana. ***Bartonella Quintana*** - **Bartonella quintana** is the bacterium responsible for causing **trench fever**, a disease historically prevalent during wartime in crowded and unsanitary conditions. - It is transmitted by the **human body louse** (*Pediculus humanus corporis*), which acts as a vector for the bacteria. *Coxiella burnetii* - **Coxiella burnetii** is the causative agent of **Q fever**, a zoonotic disease typically transmitted to humans through contact with infected animals or their products. - Its clinical presentation often includes acute fever, pneumonia, and hepatitis, which differs from the characteristic relapsing fever of trench fever. *R. tsutsugamushi* - **R. tsutsugamushi** (also known as *Orientia tsutsugamushi*) causes **scrub typhus**, a mite-borne disease common in rural areas of Asia and Australia. - The disease is characterized by a distinctive eschar, lymphadenopathy, and maculopapular rash, which are not typical features of trench fever. *R. prowazekii* - **R. prowazekii** is the bacterium responsible for **epidemic typhus** (louse-borne typhus), which shares the human body louse as a vector with trench fever. - However, epidemic typhus presents with a sustained high fever, rash that spreads centrifugally, and severe systemic symptoms, differentiating it from the relapsing fever patterns of trench fever.

Question 1

In a clinical scenario where a patient presents with flaccid paralysis, which of the following toxins is most likely responsible?

Accepted Answer

Botulism

Answer

Tetanus

Answer

Diphtheria

Answer

Cholera

Question 2

Blood culture is positive in which infection caused by Staphylococcus aureus?

Accepted Answer

Infective endocarditis

Answer

Impetigo

Answer

Toxic Shock Syndrome (TSS)

Answer

Staphylococcal Scalded Skin Syndrome (SSSS)

Question 3

Which of the following statements about Enterohemorrhagic E. coli (EHEC) is false?

Accepted Answer

Sereny test is positive

Answer

Commonly causes HUS

Answer

Bloody diarrhea and HUS linked to O157:H7

Answer

Produces Shiga-like toxin

Question 4

Which of the following is more frequently associated with Klebsiella pneumoniae than with Pseudomonas aeruginosa?

Accepted Answer

Upper lobe cavitation

Answer

Cystic fibrosis

Answer

Diabetes mellitus

Answer

Artificial ventilation

Question 5

Atrophic dry nasal mucosa, extensive encrustations, and a woody hard external nose are most suggestive of:

Accepted Answer

Klebsiella pneumoniae

Answer

Bacteroides

Answer

Staphylococcus aureus

Answer

Peptostreptococcus

Question 6

Which of the following is the MOST CHARACTERISTIC feature of Campylobacter?

Accepted Answer

Comma-shaped

Answer

Non-motile

Answer

Encapsulated

Answer

Spore-forming

Question 7

Which of the following is a true statement regarding Enterobacteriaceae?

Accepted Answer

All members are oxidase negative

Answer

Glucose is fermented by most members of the family

Answer

Motility in Enterobacteriaceae is via peritrichous flagella

Answer

Nitrate reduction positive

Question 8

A 26-year-old male patient presented with a granulomatous penile ulcer. On Wright Giemsa staining, tiny organisms of 2 microns are seen engulfed by macrophages. What is the causative organism?

Accepted Answer

Donovanosis (Calymmatobacterium granulomatis)

Answer

Lymphogranuloma venereum (LGV)

Answer

Gonorrhea (Neisseria gonorrhoeae)

Answer

Syphilis (Treponema pallidum)

Question 9

Which of the following organisms is an obligate intracellular bacterium that commonly causes sexually transmitted infections?

Accepted Answer

Chlamydia

Answer

Mycoplasma

Answer

Rickettsia

Answer

Prion

Question 10

Causative agent of trench fever is which of the following?

Accepted Answer

Bartonella quintana

Answer

Coxiella burnetii

Answer

R. tsutsugamushi

Answer

R. prowazekii

Bacteriology — MCQs

Bacteriology — MCQs

On this page

Practice by Chapter

Want unlimited practice?