Bacteriology Practice Questions

Q: A person returns to Delhi from Bangladesh after 2 days and has diarrhea. Stool examination shows RBC's in stool. The likely organism causing is ?

Shigella dysenteriae. ***Shigella dysenteriae*** - This organism causes **bacillary dysentery**, characterized by fever, abdominal cramps, and frequent, small-volume stools containing **blood and mucus (RBCs)**, which fits the clinical picture of a traveler experiencing diarrhea with RBCs in stool. - The rapid onset (within 2 days of return) and the presence of **RBCs in stool** are highly suggestive of an invasive bacterial pathogen like *Shigella*. *Enteropathogenic E. Coli* - **EPEC** typically causes **watery diarrhea**, particularly in infants, by disrupting intestinal microvilli. - It does **not usually cause bloody stools** or significant red blood cells in the stool. *Salmonella typhi* - While *Salmonella typhi* causes **typhoid fever**, its initial presentation is typically with fever, headache, and constipation, followed by a **pea-soup diarrhea** in later stages, which is usually not bloody. - The rapid onset of bloody diarrhea within 2 days is less characteristic of typhoid fever, which has a longer incubation period. *Enterotoxigenic E. Coli* - **ETEC** is a common cause of **traveler's diarrhea**, but it produces toxins that lead to **watery, non-bloody diarrhea**. - The presence of **RBCs in the stool** makes ETEC an unlikely cause in this scenario.

Q: Regarding Chlamydia infection of the eyes, true statements include the following except:

Penicillin is the treatment. ***Penicillin is the treatment*** - **Penicillin** is ineffective against *Chlamydia trachomatis* because *Chlamydia* lacks a **peptidoglycan cell wall**, which is the target of penicillin. - The standard treatment for chlamydial infections, including ocular infections, involves **azithromycin** or **doxycycline**. *Inclusion conjunctivitis is an acute ocular infection caused by sexually transmitted C. trachomatis strains (usually serovars D through K)* - **Inclusion conjunctivitis** is indeed caused by sexually transmitted serovars of *Chlamydia trachomatis* (typically **D through K**). - It usually occurs in sexually active adults and can affect neonates through maternal transmission. *Can be cultured* - *Chlamydia* are **obligate intracellular bacteria**, meaning they can only replicate inside host cells. - While they can be grown in cell cultures, this is a specialized technique and not a typical method for routine diagnosis due to its complexity and time-consuming nature. *Acute inclusion conjunctivitis typically presents with mucopurulent discharge* - **Acute inclusion conjunctivitis** is characterized by a **mucopurulent discharge**, along with **follicular conjunctivitis** and sometimes **preauricular lymphadenopathy**. - This discharge results from the inflammatory response to the chlamydial infection in the conjunctiva.

Q: All of the following cause Fournier's gangrene except:

Clostridium. ***Clostridium*** - While *Clostridium* species (especially *C. perfringens*) **CAN be isolated** from Fournier's gangrene cases and contribute to gas formation and tissue necrosis, they are **less commonly identified as primary pathogens** compared to other organisms. - In the context of this question, *Clostridium* is considered the "except" option because it is **relatively less frequently implicated** in Fournier's gangrene compared to the other listed organisms, though it is NOT entirely excluded from the microbiology of this condition. - *Clostridium* species are more classically associated with **gas gangrene (clostridial myonecrosis)** in traumatic wounds and deep muscle tissue. *Bacteroides* - ***Bacteroides fragilis*** and other **anaerobic gram-negative bacilli** are among the **most commonly isolated organisms** in Fournier's gangrene. - They produce enzymes that facilitate tissue destruction and contribute significantly to the **polymicrobial synergistic necrotizing infection**. - Essential component of the typical microbial flora in perianal and genital infections. *Streptococcus* - ***Streptococcus pyogenes*** (Group A Streptococcus) and other streptococcal species are **frequently isolated** from Fournier's gangrene. - They produce toxins and enzymes causing **rapid necrotizing fasciitis** with systemic toxicity. - Major contributor to the aggressive nature and rapid progression of the infection. *Staphylococcus* - ***Staphylococcus aureus*** (including MRSA) is **commonly found** in polymicrobial Fournier's gangrene infections. - Contributes to local tissue destruction through toxin production and enzyme activity. - Often isolated from perianal and genital skin flora, facilitating its involvement in these infections.

Q: In children commonest organ involved in nocardiosis is

Lungs. ***Lungs*** - The **lungs** are the primary site of infection for **Nocardia** in both adults and children, as the pathogen is typically acquired via **inhalation**. - **Pulmonary nocardiosis** can manifest as pneumonia, nodules, or cavitary lesions, especially in immunocompromised individuals. *Brain* - While the **brain** can be involved in nocardiosis, leading to **abscesses**, it is usually a result of **hematogenous dissemination** from a primary pulmonary infection, making it a secondary rather than the commonest primary site. - **Cerebral nocardia** is a serious complication, but it does not represent the initial presentation in most cases. *Skin* - **Cutaneous nocardiosis** can occur through direct inoculation into the skin following trauma, but it is less common than pulmonary involvement in children. - Such infections may present as pustules, cellulitis, or subcutaneous abscesses, usually localized to the site of injury. *Renal* - **Renal involvement** in nocardiosis is rare and typically occurs via **hematogenous spread** from a primary site, often the lungs. - It can lead to **renal abscesses** but is not considered a common initial presentation or primary site of infection.

Q: Causative organism of "glanders" is:

Burkholderia mallei. ***Burkholderia mallei*** - **_Burkholderia mallei_** is the bacterial species responsible for causing **glanders**, a contagious disease primarily affecting horses, donkeys, and mules. - Humans can contract glanders through direct contact with infected animals or contaminated materials, with respiratory and cutaneous forms of the disease being common. *Pseudomonas pseudomallei* - **_Pseudomonas pseudomallei_** (`_Burkholderia pseudomallei_`) is the causative agent of **melioidosis**, a severe infection with a wide range of clinical manifestations. - While it's closely related to _Burkholderia mallei_, melioidosis is distinct from glanders and typically found in tropical and subtropical regions. *Leptospira* - **_Leptospira_** is a spirochete bacterium responsible for **leptospirosis**, a zoonotic disease that affects both animals and humans. - It is typically transmitted through contact with water or soil contaminated with the urine of infected animals, presenting with fever, headache, body aches, and sometimes severe organ damage. *Chlamydia* - **_Chlamydia_** is a genus of intracellular bacteria known for causing a variety of infections in humans, including sexually transmitted infections (STIs), eye infections (`_trachoma_`), and respiratory infections. - It is not associated with glanders, which is caused by a distinct bacterial species with a different mode of transmission and host range.

Q: The commonest organism causing Empyema in a child under 2 years -

Pneumococcus. ***Pneumococcus*** - **Streptococcus pneumoniae (Pneumococcus)** is the most common bacterial cause of **empyema** in children across all age groups, including those under 2 years. - It accounts for **40-70% of pediatric empyema cases**, typically developing as a complication of pneumonia. - Even in the post-pneumococcal vaccine era, S. pneumoniae remains the leading cause, though serotype distribution has changed. *Staphylococcus* - **Staphylococcus aureus** is the **second most common** cause of empyema in children under 2 years, accounting for 10-30% of cases. - It causes more severe, rapidly progressing infections with significant **pleural effusion** and **necrotizing pneumonia**. - While historically prominent, it is no longer the most common cause in the modern antibiotic era. *Klebsiella* - **Klebsiella pneumoniae** is a less common cause of empyema in children, more frequently seen in immunocompromised patients or those with underlying chronic diseases. - It is not a typical cause of empyema in otherwise healthy children under 2 years old. *E. Coli* - **Escherichia coli** can cause empyema, particularly in neonates, immunocompromised patients, or as a complication of intra-abdominal infections. - It is a rare cause of empyema in the typical pediatric population under 2 years without specific predisposing factors.

Q: Which of the following causes Melioidosis?

Burkholderia pseudomallei. ***Burkholderia pseudomallei*** - **Melioidosis** is caused by the bacterium **_Burkholderia pseudomallei_**, a **Gram-negative rod** found in soil and water. - This organism is endemic in tropical and subtropical regions, particularly Southeast Asia and northern Australia, and can cause a wide spectrum of disease from asymptomatic infection to fulminant sepsis. *Burkholderia cepacia* - **_Burkholderia cepacia complex_** is a group of bacteria known to cause infections, particularly in individuals with **cystic fibrosis** or **immunocompromised states**. - While it can cause opportunistic infections, it is not the causative agent of melioidosis. *Burkholderia mallei* - **_Burkholderia mallei_** is the causative agent of **glanders**, a contagious disease primarily affecting **horses, donkeys, and mules**, which can be transmitted to humans. - It is related to **_B. pseudomallei_** but does not cause melioidosis. *None of the options* - This option is incorrect because **_Burkholderia pseudomallei_** is the specific and well-established causative agent of melioidosis.

Q: A mother brings her 1-year-old daughter to the physician. She says that for the last 2 days her daughter has been fussy and crying more than usual. She also refuses formula. The patient has a fever of 39.4degC (102.9degF). Meningitis is suspected, and a lumbar puncture is performed. Analysis of the cerebrospinal fluid shows an opening pressure of 98 mm H2O, a leukocyte count of 1256/mm3, a protein level of 210 mg/dL, and a glucose level of 31 mg/dL.. The mother says that the patient has received no immunizations. Which of the following organisms is most likely responsible for this patient's illness?

Haemophilus influenzae. ***Haemophilus influenzae*** - *H. influenzae* type b (Hib) is the **most common cause of bacterial meningitis** in unvaccinated children aged 6 months to 5 years. - Before the introduction of the Hib vaccine, this organism was the **leading cause** of bacterial meningitis in this age group. - The CSF profile (high leukocyte count with **neutrophil predominance**, elevated protein >100 mg/dL, and low glucose <40 mg/dL) is classic for **bacterial meningitis**. - In an **unimmunized 1-year-old**, Hib remains the most likely pathogen. *Streptococcus pneumoniae* - *S. pneumoniae* is a common cause of bacterial meningitis across all age groups and is now the **most common cause in vaccinated populations** where Hib has been eliminated. - However, in an **unvaccinated child** of this age, *H. influenzae* type b is statistically more likely. - The CSF findings would be identical and cannot distinguish between these two organisms. *Group B Streptococcus* - **Group B Streptococcus** (*Streptococcus agalactiae*) primarily causes **early-onset neonatal meningitis** (first week of life) and **late-onset neonatal meningitis** (up to 3 months of age). - While late-late onset can occur beyond 3 months, it is uncommon at 1 year of age. - This organism is not a typical cause of meningitis in this age group. *Neisseria meningitidis* - *N. meningitidis* causes bacterial meningitis primarily in **older children, adolescents, and young adults**, often associated with outbreaks. - While possible in a 1-year-old, it is less common than Hib in unvaccinated children of this age. - Meningococcal meningitis is often associated with a **petechial or purpuric rash**, which is not mentioned in this case.

Q: Which of the following is true about typhoid?

Vi antibodies are present in about 80% of chronic carriers. ***Vi antibodies are present in about 80% of chronic carriers*** - The detection of **Vi antibodies** is a useful serological marker for identifying chronic carriers of *Salmonella Typhi*. - Approximately **80% of chronic typhoid carriers** produce measurable levels of Vi antibodies, making it a valuable screening tool. *Gall bladder usually not involved in carrier state* - The **gallbladder** is the primary site of chronic carriage for *Salmonella Typhi*, where the bacteria persist and are shed in the feces. - Presence of **gallstones** can further contribute to the persistence of infection and chronic carriage in the gallbladder. *Tetracycline is the DOC for carriers* - **Fluoroquinolones** (e.g., ciprofloxacin) or **amoxicillin** are typically the drugs of choice for treating typhoid carriers, often given for an extended period. - **Tetracycline** is generally not recommended for treating typhoid carriers due to resistance and less effective eradication rates. *Fecal carriers are less common* - **Fecal carriers** are the most common form of chronic typhoid carriage, where *Salmonella Typhi* is shed in the feces for more than a year. - Urinary carriers are less common but can occur, especially in individuals with **schistosomiasis**.

Q: Which does not cause skin involvement -

M. Kansasii. ***M. Kansasii*** - While *M. kansasii* is a **nontuberculous mycobacterium**, it primarily causes **pulmonary disease** similar to tuberculosis, especially in individuals with compromised immune systems. - Skin involvement is **rare** and not a typical presentation for *M. kansasii* infections. *M. tuberculosis* - **Cutaneous tuberculosis** can manifest in various forms, including **lupus vulgaris**, scrofuloderma, and tuberculosis verrucosa cutis. - Skin involvement occurs due to direct inoculation, contiguous spread, or lymphatic/hematogenous dissemination. *M. Ulcerans* - *M. ulcerans* is the causative agent of **Buruli ulcer**, a devastating skin infection characterized by large, necrotic ulcers. - It produces **mycolactone**, a toxin that causes tissue destruction and immunosuppression in the affected area. *M. Marinum* - *M. marinum* typically causes **"fish tank granuloma"** or "swimming pool granuloma," an infection acquired through exposure to contaminated water. - It results in chronic skin lesions, often granulomatous nodules or ulcers, primarily on exposed extremities.

Question 1

A person returns to Delhi from Bangladesh after 2 days and has diarrhea. Stool examination shows RBC's in stool. The likely organism causing is ?

Accepted Answer

Shigella dysenteriae

Answer

Enteropathogenic E. Coli

Answer

Salmonella typhi

Answer

Enterotoxigenic E. Coli

Question 2

Regarding Chlamydia infection of the eyes, true statements include the following except:

Accepted Answer

Penicillin is the treatment

Answer

Inclusion conjunctivitis is an acute ocular infection caused by sexually transmitted C. trachomatis strains (usually serovars D through K)

Answer

Can be cultured

Answer

Acute inclusion conjunctivitis typically presents with mucopurulent discharge

Question 3

All of the following cause Fournier's gangrene except:

Accepted Answer

Clostridium

Answer

Bacteroides

Answer

Streptococcus

Answer

Staphylococcus

Question 4

In children commonest organ involved in nocardiosis is

Accepted Answer

Lungs

Answer

Brain

Answer

Skin

Answer

Renal

Question 5

Causative organism of "glanders" is:

Accepted Answer

Burkholderia mallei

Answer

Pseudomonas pseudomallei

Answer

Leptospira

Answer

Chlamydia

Question 6

The commonest organism causing Empyema in a child under 2 years -

Accepted Answer

Pneumococcus

Answer

Staphylococcus

Answer

Klebsiella

Answer

E.Coli

Question 7

Which of the following causes Melioidosis?

Accepted Answer

Burkholderia pseudomallei

Answer

Burkholderia cepacia

Answer

Burkholderia mallei

Answer

None of the options

Question 8

A mother brings her 1-year-old daughter to the physician. She says that for the last 2 days her daughter has been fussy and crying more than usual. She also refuses formula. The patient has a fever of 39.4degC (102.9degF). Meningitis is suspected, and a lumbar puncture is performed. Analysis of the cerebrospinal fluid shows an opening pressure of 98 mm H2O, a leukocyte count of 1256/mm3, a protein level of 210 mg/dL, and a glucose level of 31 mg/dL.. The mother says that the patient has received no immunizations. Which of the following organisms is most likely responsible for this patient's illness?

Accepted Answer

Haemophilus influenzae

Answer

Group B Streptococcus

Answer

Neisseria meningitidis

Answer

Streptococcus pneumoniae

Question 9

Which of the following is true about typhoid?

Accepted Answer

Vi antibodies are present in about 80% of chronic carriers

Answer

Gall bladder usually not involved in carrier state

Answer

Tetracycline is the DOC for carriers

Answer

Fecal carriers are less common

Question 10

Which does not cause skin involvement -

Accepted Answer

M. Kansasii

Answer

M. tuberculosis

Answer

M. Ulcerans

Answer

M. Marinum

Bacteriology — MCQs

Bacteriology — MCQs

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