Bacteriology Practice Questions

Q: Burkholderia cepacia is resistant to which of the following antibiotics?

Cefotetan. ***Cefotetan*** - *Burkholderia cepacia* shows **consistent resistance** to second-generation cephalosporins and cephamycins like **cefotetan**. - This organism is intrinsically resistant to **aminoglycosides** (gentamicin, tobramycin) and **polymyxins** (colistin), and shows variable resistance to many beta-lactams. - Among the options provided, cefotetan represents the most consistently ineffective agent. *Ceftazidime* - **Ceftazidime** (third-generation cephalosporin) shows **variable susceptibility** with *B. cepacia*. - While resistance is common, it is **not uniform**, and ceftazidime is sometimes used in **combination therapy** for B. cepacia infections. - Not considered a classic example of intrinsic resistance. *Trimethoprim-sulfamethoxazole* - **TMP-SMX** is the **first-line treatment** for *Burkholderia cepacia* infections. - It demonstrates good activity and is the preferred antimicrobial agent for this organism. - Resistance can develop but is not intrinsic. *Temocillin* - **Temocillin** (carboxypenicillin) has demonstrated activity against *B. cepacia*. - Used particularly in Europe for treating infections caused by this organism. - Not an antibiotic to which *B. cepacia* shows consistent resistance.

Q: Which condition is associated with Streptococcus bovis infection?

Colorectal cancer. ***Colorectal cancer*** - *Streptococcus gallolyticus* (formerly known as *Streptococcus bovis* biotype I) infection, particularly **bacteremia** or **endocarditis**, has a strong association with underlying **colorectal cancer**. - It is hypothesized that the bacteria may play a role in **tumorigenesis** or that the cancerous lesions provide an entry point for the bacteria into the bloodstream. *Chronic lymphocytic leukemia (CLL)* - While patients with CLL are **immunocompromised** and prone to infections, there is no specific association between *Streptococcus bovis* and CLL. - Infections in CLL patients are typically due to encapsulated bacteria, such as *Streptococcus pneumoniae* or *Haemophilus influenzae*. *Hairy cell leukemia (HCL)* - Patients with HCL often experience **immunosuppression** due to neutropenia and monocytopenia, leading to increased susceptibility to infections. - However, there is no direct or specific link between *Streptococcus bovis* infection and HCL itself. *Multiple myeloma (MM)* - Patients with multiple myeloma have **impaired humoral immunity** and are at risk for infections, especially from encapsulated bacteria. - There is no established specific association between *Streptococcus bovis* infection and multiple myeloma.

Q: Which microorganism is the most common cause of pyogenic osteomyelitis?

S. aureus. ***Staph aureus*** - **_Staphylococcus aureus_** is the most frequent cause of **pyogenic osteomyelitis** across all age groups and routes of infection. - Its ability to adhere to bone, form biofilms, and produce toxins contributes to its prevalence in bone infections. *Streptococcus spp.* - While various **_Streptococcus_** species can cause infections, they are less common causes of pyogenic osteomyelitis compared to **_Staphylococcus aureus_**. - **Group A _Streptococcus_** can cause severe invasive infections but rarely involves primary bone infection. *Corynebacterium spp.* - **_Corynebacterium_** species, particularly **_Corynebacterium striatum_**, are increasingly recognized as opportunistic pathogens, especially in immunocompromised individuals or those with foreign bodies. - However, they are not the most common cause of osteomyelitis in the general population. *Neisseria gonorrhoeae (gonococcus)* - **_Neisseria gonorrhoeae_** can cause **disseminated gonococcal infection (DGI)**, which may include joint involvement (**septic arthritis**). - While it can lead to bone pain and swelling, it primarily affects joints and is a less common cause of direct **pyogenic osteomyelitis** than **_S. aureus_**.

Q: What is the most common age group affected by Streptococcus pyogenes?

5-15 years. ***5-15 years*** - **Streptococcus pyogenes** (Group A Strep) commonly causes **pharyngitis** (strep throat), which primarily affects school-aged children. - This age group is more susceptible due to increased exposure in school and daycare settings. *<5 years* - While younger children can get strep infections, it is less common in those under **3 years of age**, as viral etiologies are more prevalent for pharyngitis in this group. - They are more prone to **non-streptococcal bacterial infections** and certain viral infections. *20-25 years* - Although adults can get **Streptococcus pyogenes** infections, the incidence significantly decreases after childhood. - Pharyngitis in this age group is more often **viral** in origin. *30-40 years* - The prevalence of **Streptococcus pyogenes** infections, particularly pharyngitis, is typically low in this age group compared to children. - Infections, if they occur, may stem from exposure to infected children or close contact environments.

Q: Granuloma inguinale is caused by:

Calymmatobacterium granulomatis. ***Calymmatobacterium granulomatis*** - **Granuloma inguinale**, also known as **donovanosis**, is a sexually transmitted infection caused by **_Calymmatobacterium granulomatis_**. - This bacterium is notoriously difficult to culture, so diagnosis is typically made by identifying **Donovan bodies** (macrophages filled with bacteria) in tissue samples. *Haemophilus ducreyi* - **_Haemophilus ducreyi_** is the causative agent of **chancroid**, - Chancroid is characterized by **painful genital ulcers** with a ragged, undermined border, and often accompanied by **tender inguinal lymphadenopathy**. *Chlamydia trachomatis* - **_Chlamydia trachomatis_** is responsible for several conditions, including **chlamydia** (the most common bacterial STI), **lymphogranuloma venereum (LGV)**, and **trachoma**. - LGV presents with a transient, often unnoticed genital lesion followed by painful, suppurative lymphadenopathy, which is distinct from granuloma inguinale. *Treponema pallidum* - **_Treponema pallidum_** is the spirochete that causes **syphilis**, which progresses through several stages. - Primary syphilis manifests as a **painless chancre**, while secondary syphilis can involve a widespread rash, lymphadenopathy, and mucosal lesions.

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

Characteristic tumbling motility at 37°C. ***Characteristic tumbling motility at 37°C*** - *Listeria monocytogenes* exhibits **"tumbling motility" at 20-25°C**, but it is non-motile at 37°C. - This temperature-dependent motility is a key diagnostic feature, and the statement claiming motility at 37°C is incorrect. *Gram positive* - *Listeria monocytogenes* is indeed a **gram-positive bacillus**, a key characteristic aiding in its initial identification. - Its gram stain reaction distinguishes it from gram-negative bacteria, guiding appropriate treatment. *PALCAM agar is used for isolation* - **PALCAM (Polymyxin Acriflavin Lithium Chloride Ceftazidime Esculin Mannitol) agar** is a selective and differential medium specifically designed for the isolation and detection of *Listeria monocytogenes*. - It utilizes esculin hydrolysis and mannitol fermentation to differentiate *Listeria* species. *Umbrella shaped growth* - When cultured in a semi-solid medium, *Listeria monocytogenes* typically displays a characteristic **umbrella-shaped pattern of growth** at reduced temperatures (e.g., 20-25°C) due to its motility. - This macroscopic appearance is a classic identifier for *Listeria*.

Q: Which type of DNase produced by Streptococcus is known to be the most antigenic in humans?

DNase B. ***DNase B*** - **DNase B** is the most **antigenic** of the four DNases (A, B, C, D) produced by *Streptococcus pyogenes*. - Antibodies against DNase B are commonly measured as anti-DNase B titers in the diagnosis of **streptococcal infections** and their sequelae, like **acute rheumatic fever** and **post-streptococcal glomerulonephritis**, especially when ASO titers are negative. *DNase A* - While *Streptococcus pyogenes* produces **DNase A**, it is not considered the most antigenically potent or clinically relevant for antibody testing in humans. - Its antigenicity is generally **lower** than that of DNase B in response to streptococcal infection. *DNase C* - **DNase C** is another deoxyribonuclease produced by *Streptococcus pyogenes*. - Similar to DNase A, it does not elicit as strong or as consistent an **antibody response** in human infections compared to DNase B. *DNase D* - **DNase D** is the fourth type of deoxyribonuclease produced by *Streptococcus pyogenes*. - Its **antigenicity** in humans is less pronounced and less diagnostically significant than that of **DNase B**.

Q: What is the clinical significance of the Vi antigen in Salmonella typhi?

Indicates carrier status in individuals. ***Indicates carrier status in individuals*** - The **Vi (Virulence) antigen** is a **capsular polysaccharide** found on *Salmonella typhi* that helps the bacterium evade immune responses - The presence of persistent **anti-Vi antibodies** is the **hallmark of chronic typhoid carriers**, particularly those harboring bacteria in the **gallbladder** - Vi antibody testing is specifically used for **carrier screening** and identification, as carriers maintain high anti-Vi titers even without active symptoms - This is the **primary clinical significance** of the Vi antigen in diagnostic microbiology *Used for diagnosing typhoid fever* - This is **incorrect** - the Vi antigen is NOT used for diagnosing acute typhoid fever - The standard **Widal test** detects antibodies against **O (somatic)** and **H (flagellar)** antigens, NOT Vi antigen - Acute diagnosis relies on **blood culture** and detection of O and H antibodies, not Vi antibodies - Vi antibodies appear later in infection and persist longer, making them markers of **chronic carriage** rather than acute disease *Stimulates an immune response* - While true that Vi antigen stimulates antibody production, this is not its **clinical significance** - All bacterial antigens stimulate immune responses - this doesn't distinguish Vi antigen's specific clinical utility - The key clinical value lies in its use for **carrier detection**, not merely immunogenicity *Not primarily used in Widal test* - This is a **true statement** but not the answer to what the clinical significance IS - The Widal test uses O and H antigens for acute diagnosis - While accurate, this option describes what Vi antigen is NOT used for, rather than its actual clinical significance as a **carrier marker**

Q: What is the causative agent of Rhinoscleroma?

Klebsiella rhinoscleromatis. ***Klebsiella rhinoscleromatis*** - This bacterium is the **specific causative agent** of rhinoscleroma, a chronic progressive granulomatous disease affecting the upper respiratory tract. - It is a sub-species of *Klebsiella pneumoniae*. *Staphylococcus aureus* - *Staphylococcus aureus* is a common cause of various **skin infections**, **abscesses**, and systemic infections like **sepsis** and **endocarditis**. - It is not associated with rhinoscleroma. *Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* is an **opportunistic pathogen** often associated with hospital-acquired infections, particularly in immunocompromised individuals. - It can cause **pneumonia**, urinary tract infections, and infections in burn patients, but not rhinoscleroma. *Corynebacterium diphtheriae* - *Corynebacterium diphtheriae* is the causative agent of **diphtheria**, characterized by the formation of a **pseudomembrane** in the throat and toxin-mediated systemic effects. - Its clinical presentation is distinct from rhinoscleroma.

Q: What is the most common cause of lung abscess in comatose patients?

Oral anaerobes. Oral anaerobes - **Comatose patients** are at high risk for **aspiration** of oropharyngeal flora, which predominantly consists of anaerobic bacteria. [1] - Aspiration of these organisms, especially in compromised lung tissue, frequently leads to **necrotizing pneumonia** and subsequent abscess formation. [1] *Staph aureus* - While *Staphylococcus aureus* can cause lung abscesses, particularly in the context of **hematogenous spread** (e.g., endocarditis) or nosocomial infections, it is not the most common cause in *comatose patients* who typically aspirate oral flora. [2] - *S. aureus* lung abscesses are often associated with multiple, smaller lesions rather than a single, large abscess from aspiration. *Klebsiella* - *Klebsiella pneumoniae* can cause severe, **rapidly progressive pneumonia** that may lead to abscess formation, especially in individuals with **alcoholism** or **diabetes**. - However, it is less common than oral anaerobes as the primary cause of abscess in the general population of comatose patients, whose main risk factor is aspiration of normal oral flora. [1] *Tuberculosis* - **Mycobacterium tuberculosis** can cause cavitary lung lesions, but these are typically chronic and result from primary or reactivated tuberculosis disease, not acute aspiration. [3] - Lung abscesses caused by tuberculosis are histologically distinct from pyogenic abscesses and are characterized by **granulomatous inflammation** and caseous necrosis.

Question 1

Burkholderia cepacia is resistant to which of the following antibiotics?

Accepted Answer

Cefotetan

Answer

Trimethoprim-sulfamethoxazole

Answer

Ceftazidime

Answer

Temocillin

Question 2

Which condition is associated with Streptococcus bovis infection?

Accepted Answer

Colorectal cancer

Answer

Chronic lymphocytic leukemia (CLL)

Answer

Hairy cell leukemia (HCL)

Answer

Multiple myeloma (MM)

Question 3

Which microorganism is the most common cause of pyogenic osteomyelitis?

Accepted Answer

S. aureus

Answer

Streptococcus spp.

Answer

Corynebacterium spp.

Answer

Neisseria gonorrhoeae (gonococcus)

Question 4

What is the most common age group affected by Streptococcus pyogenes?

Accepted Answer

5-15 years

Answer

30-40 years

Answer

<5 years

Answer

20-25 years

Question 5

Granuloma inguinale is caused by:

Accepted Answer

Calymmatobacterium granulomatis

Answer

Haemophilus ducreyi

Answer

Chlamydia trachomatis

Answer

Treponema pallidum

Question 6

Which of the following statements about Listeria is false?

Accepted Answer

Characteristic tumbling motility at 37°C

Answer

PALCAM agar is used for isolation

Answer

Gram positive

Answer

Umbrella shaped growth

Question 7

Which type of DNase produced by Streptococcus is known to be the most antigenic in humans?

Accepted Answer

DNase B

Answer

DNase C

Answer

DNase D

Answer

DNase A

Question 8

What is the clinical significance of the Vi antigen in Salmonella typhi?

Accepted Answer

Indicates carrier status in individuals

Answer

Stimulates an immune response

Answer

Not primarily used in Widal test

Answer

Used for diagnosing typhoid fever

Question 9

What is the causative agent of Rhinoscleroma?

Accepted Answer

Klebsiella rhinoscleromatis

Answer

Staphylococcus aureus

Answer

Pseudomonas aeruginosa

Answer

Corynebacterium diphtheriae

Question 10

What is the most common cause of lung abscess in comatose patients?

Accepted Answer

Oral anaerobes

Answer

Staph aureus

Answer

Klebsiella

Answer

Tuberculosis

Bacteriology — MCQs

Bacteriology — MCQs

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