Bacteriology Practice Questions

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.

Q: In a 6 months old baby, floppy infant syndrome is seen commonly due to infection with ?

Clostridium Botulinum. ***Clostridium Botulinum*** - **Infant botulism** is caused by the ingestion of **_Clostridium botulinum_ spores**, which colonize the infant's immature gut and produce neurotoxins. - The classic presentation is **floppy infant syndrome**, characterized by **hypotonia**, **weakness**, feeding difficulties, and constipation. *Clostridium welchii* - This is an outdated name for **_Clostridium perfringens_**, which is primarily associated with **food poisoning** and **gas gangrene**. - It does not cause floppy infant syndrome. *Clostridium septicum* - **_Clostridium septicum_** is known to cause **spontaneous gas gangrene** and is often associated with neutropenic enterocolitis (typhlitis). - It is not a cause of floppy infant syndrome. *Clostridium tetani* - **_Clostridium tetani_** produces **tetanospasmin**, a neurotoxin that causes **tetanus**, characterized by muscle spasms and rigidity (lockjaw). - It does not cause the flaccid paralysis seen in floppy infant syndrome.

Q: "Chancroid" is caused by:

H. ducreyi. ***H. ducreyi*** - **Chancroid** is a sexually transmitted infection characterized by painful genital ulcers and is specifically caused by the bacterium **_Haemophilus ducreyi_**. - This organism creates soft chancres (ulcers) that often bleed easily and are frequently accompanied by painful swelling of the lymph nodes in the groin. *H. influenzae* - **_Haemophilus influenzae_** is a common cause of respiratory tract infections, such as otitis media, sinusitis, and pneumonia, and can also lead to meningitis. - It is not associated with sexually transmitted infections or genital ulcers, and therefore does not cause chancroid. *H. aprophilus* - **_Haemophilus aphrophilus_** (now reclassified as _Aggregatibacter aphrophilus_) is a rare cause of human infections, primarily associated with endocarditis and brain abscesses. - This bacterium is part of the **HACEK group** of gram-negative bacteria known to cause infective endocarditis and is not involved in chancroid. *All of the options* - While all listed organisms are types of _Haemophilus_ or former _Haemophilus_ species, only **_H. ducreyi_** specifically causes chancroid. - The other options are responsible for different types of infections and do not cause genital ulcers characteristic of chancroid.

Q: Salmonella typhi is the causative agent of typhoid fever. The infective dose of S. typhi is -

10^2-10^5 bacilli. ***10^2-10^5 bacilli*** - The infective dose of **Salmonella typhi** is relatively low compared to other enteric pathogens, typically ranging from **100 to 100,000 bacteria**. - This low infective dose contributes to its high transmissibility and ability to cause widespread outbreaks. *10^8-10^10 bacilli* - This range represents a significantly **higher infective dose**, which is characteristic of some less virulent or more easily cleared enteric bacteria. - If **Salmonella typhi** required such a high dose, typhoid fever would be a much rarer disease. *1-10 bacilli* - An infective dose this low is characteristic of highly pathogenic organisms with extreme virulence or unique immune evasion mechanisms, such as **Shigella**. - While **Salmonella typhi** is virulent, its infective dose is not typically in this single-digit range. *One bacillus* - It is highly improbable for a single bacterium to consistently establish infection and cause a systemic disease like typhoid fever, even for highly virulent pathogens. - Effective infection usually requires a minimum threshold of bacteria to overcome host defenses and replicate.

Q: Refrigerated blood stored up to 48 hours before transfusion can destroy which of the following ?

Treponema pallidum. ***Treponema pallidum*** - *Treponema pallidum*, the causative agent of **syphilis**, is highly sensitive to cold temperatures and **does not survive well in refrigerated blood** stored for more than a few days (typically 24-48 hours). - This characteristic makes the risk of **transfusion-transmitted syphilis** extremely low for stored blood components. *Hepatitis B* - **Hepatitis B virus (HBV)** is very hardy and can survive for extended periods, even in refrigerated blood. - Blood donations are routinely screened for HBV to prevent **transfusion-associated hepatitis**. *P. Vivax* - *Plasmodium vivax*, one of the species causing **malaria**, can survive in refrigerated blood, as the parasites can remain viable within red blood cells [1]. - Transmission of malaria through blood transfusion is a known risk, especially in endemic areas, and is not mitigated by refrigeration alone. *HIV* - **Human Immunodeficiency Virus (HIV)** can survive in refrigerated whole blood and blood components for the duration of their typical storage periods. - Therefore, strict screening of blood donors for HIV antibodies and antigens is crucial to prevent **transfusion-related HIV transmission**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 398-400.

Q: Xanthogranulomatous pyelonephritis is most characteristically associated with:

Proteus. ***Proteus*** - **Proteus mirabilis** is most characteristically associated with xanthogranulomatous pyelonephritis due to its ability to produce **urease**, which hydrolyzes urea to ammonia and carbon dioxide. - This leads to the formation of **struvite stones (magnesium ammonium phosphate)**, causing chronic obstruction and infection, which are key predisposing factors for XGPN. - The classic presentation involves **staghorn calculi** with Proteus infection. *E. coli* - While **E. coli** is the most frequently isolated organism in XGPN cases (found in up to 50% of cases), it is not as specifically associated with the characteristic pathophysiology. - E. coli is the most common cause of uncomplicated UTIs and acute pyelonephritis but lacks the urease production that drives struvite stone formation. *Pseudomonas* - **Pseudomonas aeruginosa** can cause severe and complicated UTIs, especially in catheterized or immunocompromised patients. - However, it is **not typically associated** with the urease activity and struvite stone formation that are hallmark features predisposing to XGPN. *Klebsiella* - **Klebsiella pneumoniae** can cause UTIs and may produce urease, leading to stone formation. - While it can be a cause of pyelonephritis, **Proteus species** are more consistently and strongly associated with the specific pathogenesis that characterizes XGPN.

Q: "School of fish" appearance with bipolar staining is characteristically shown by?

Hemophilus ducreyi. ***Hemophilus ducreyi*** - This bacterium, the causative agent of **chancroid**, classically exhibits a **"school of fish" appearance** with prominent **bipolar staining** when viewed on Gram stain. - The organisms appear as pleomorphic Gram-negative coccobacilli arranged in chains or groups, with bipolar staining giving each bacterium a characteristic appearance. - Identification is typically done through **Gram stain** of a sample from the ulcer base, revealing this distinctive morphology. *Chlamydia* - **Chlamydia trachomatis** is an obligate intracellular bacterium and does not display this morphology; it appears as elementary or reticulate bodies within host cells. - It is known for causing sexually transmitted infections such as **chlamydia** and **lymphogranuloma venereum**. - Cannot be visualized by standard Gram staining. *Donovani granulomatis* - This bacterium, now reclassified as **Klebsiella granulomatis**, causes **granuloma inguinale (donovanosis)** and is characterized by the presence of **Donovan bodies** within macrophages. - Donovan bodies are encapsulated rod-shaped bacteria with a characteristic "closed safety pin" appearance found in the cytoplasm of host cells. - Does not show the "school of fish" arrangement. *Mycoplasma* - **Mycoplasma** species are the smallest free-living bacteria lacking a cell wall, which gives them a pleomorphic (variable) shape. - They do not exhibit bipolar staining or the "school of fish" appearance and cannot be visualized by Gram stain. - Associated with conditions like **atypical pneumonia** and **urethritis**.

Question 1

Which of the following causes Melioidosis?

Accepted Answer

Burkholderia pseudomallei

Answer

Burkholderia cepacia

Answer

Burkholderia mallei

Answer

None of the options

Question 2

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 3

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 4

Which does not cause skin involvement -

Accepted Answer

M. Kansasii

Answer

M. tuberculosis

Answer

M. Ulcerans

Answer

M. Marinum

Question 5

In a 6 months old baby, floppy infant syndrome is seen commonly due to infection with ?

Accepted Answer

Clostridium Botulinum

Answer

Clostridium welchii

Answer

Clostridium septicum

Answer

Clostridium tetani

Question 6

"Chancroid" is caused by:

Accepted Answer

H. ducreyi

Answer

H. influenzae

Answer

All of the options

Answer

H. aphrophilus

Question 7

Salmonella typhi is the causative agent of typhoid fever. The infective dose of S. typhi is -

Accepted Answer

10^2-10^5 bacilli

Answer

10^8-10^10 bacilli

Answer

1-10 bacilli

Answer

One bacillus

Question 8

Refrigerated blood stored up to 48 hours before transfusion can destroy which of the following ?

Accepted Answer

Treponema pallidum

Answer

Hepatitis B

Answer

P. Vivax

Answer

HIV

Question 9

Xanthogranulomatous pyelonephritis is most characteristically associated with:

Accepted Answer

Proteus

Answer

E. coli

Answer

Pseudomonas

Answer

Klebsiella

Question 10

"School of fish" appearance with bipolar staining is characteristically shown by?

Accepted Answer

Hemophilus ducreyi

Answer

Chlamydia

Answer

Donovani granulomatis

Answer

Mycoplasma

Bacteriology — MCQs

Bacteriology — MCQs

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