Bacteriology Practice Questions

Q: Which organism causes toxic shock syndrome?

Staphylococcus aureus. ***Staphylococcus aureus*** - **_S. aureus_** produces **toxic shock syndrome toxin-1 (TSST-1)** or other superantigens, which are potent activators of T cells, leading to a massive cytokine release and the systemic inflammatory response characteristic of **toxic shock syndrome**. - **TSST-1** is responsible for most cases of menstrual toxic shock syndrome, often associated with tampons, while non-menstrual cases can arise from surgical wounds, burns, or other local infections. *Pneumococcus* - **_Streptococcus pneumoniae_** (Pneumococcus) is a common cause of **pneumonia**, **otitis media**, and **meningitis**, but it does not produce toxins that cause toxic shock syndrome. - Its pathogenicity is primarily due to its **capsule**, which helps it evade phagocytosis, rather than superantigen production. *E. coli* - **_Escherichia coli_** is a gram-negative bacterium primarily known for causing **urinary tract infections**, **sepsis**, and **gastroenteritis** (e.g., traveler's diarrhea) through various toxins like **Shiga toxin** or **heat-labile/stable toxins**. - While it can cause severe systemic infections, it is not associated with the production of superantigens leading to toxic shock syndrome. *Enterococcus* - **_Enterococcus_** species (e.g., **_E. faecalis_**, **_E. faecium_**) are common causes of nosocomial infections, particularly **urinary tract infections**, **endocarditis**, and **wound infections**. - They are known for their **antibiotic resistance** but do not produce the specific superantigens associated with toxic shock syndrome.

Q: The following gram stain image shows which bacteria?

Staphylococcus aureus. ***Staphylococcus aureus*** - This image clearly shows **Gram-positive cocci** arranged in irregular, grape-like **clusters**, which is the classic microscopic appearance of *Staphylococcus* species, including *Staphylococcus aureus* - The purple color indicates they are **Gram-positive** bacteria - **Cluster arrangement** is the key distinguishing feature of staphylococci on Gram stain *Vibrio cholerae* - *Vibrio cholerae* is a **Gram-negative, comma-shaped bacillus** and would appear as pink/red, curved rods, not purple cocci - The morphology in the image is completely different from Vibrio species *Listeria monocytogenes* - *Listeria monocytogenes* is a **Gram-positive rod** (bacillus), not a coccus - It would appear as purple, rod-shaped bacteria, not spherical cocci - Its characteristic morphology is quite different from the cocci seen in the image *Streptococcus pneumoniae* - *Streptococcus pneumoniae* is a **Gram-positive coccus** but typically appears in **pairs (diplococci)** or short chains, often lancet-shaped - The bacteria in the image are predominantly in **clusters**, which differentiates them from *Streptococcus pneumoniae* - Streptococci arrange in chains or pairs, not grape-like clusters

Q: Vector of trench fever is which one of the following?

Louse. ***Louse*** - **Trench fever** is caused by the bacterium *Bartonella quintana* and is primarily transmitted to humans by the **body louse** (*Pediculus humanus corporis*). - The disease became notorious during World War I due to its prevalence among soldiers living in crowded, unhygienic conditions, which favored louse infestation. *Tick* - Ticks are vectors for various diseases such as **Lyme disease**, **Rocky Mountain spotted fever**, and **Ehrlichiosis**, but not trench fever. - These diseases are caused by different bacterial species and present with distinct clinical manifestations. *Mite* - Mites are known vectors for diseases like **scrub typhus** (transmitted by chiggers) and can cause conditions such as **scabies**, but they do not transmit trench fever. - Mites typically live on or in the skin of their hosts, and their biting patterns and associated pathogens differ from those of lice. *Rat flea* - **Rat fleas** (*Xenopsylla cheopis*) are the primary vectors for **bubonic plague** (caused by *Yersinia pestis*) and **murine typhus** (caused by *Rickettsia typhi*). - These diseases are distinct from trench fever in their causative agents, transmission cycles, and clinical presentations.

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

Group A Streptococcus is catalase positive. ***Group A Streptococcus is catalase positive*** - This statement is false because all species of **Streptococcus**, including Group A Streptococcus (GAS), are **catalase-negative**. - The absence of the **catalase enzyme** is a key differentiating feature between streptococci and staphylococci, which are catalase-positive. *Group B causes neonatal meningitis* - **Group B Streptococcus (GBS)**, or *Streptococcus agalactiae*, is a well-known cause of **neonatal meningitis** and sepsis. - Infants can acquire GBS during passage through the birth canal from a colonized mother, leading to severe infections. *Group B lives in female genital tract* - GBS is a common commensal organism found in the **lower gastrointestinal** and **female genital tracts** of up to 30% of healthy women. - Its presence in the female genital tract poses a risk for transmission to neonates during childbirth. *Classification by Lancefield based on carbohydrate antigen* - The **Lancefield grouping system** classifies streptococci based on the presence of specific **carbohydrate antigens** in their cell walls. - This serological classification, developed by Rebecca Lancefield, divides streptococci into groups A, B, C, D, F, and G, which helps in identifying different species and their associated pathologies.

Question 1

Which organism causes toxic shock syndrome?

Accepted Answer

Staphylococcus aureus

Answer

Pneumococcus

Answer

E. coli

Answer

Enterococcus

Question 2

The following gram stain image shows which bacteria?

Accepted Answer

Staphylococcus aureus

Answer

Listeria monocytogenes

Answer

Vibrio cholerae

Answer

Streptococcus pneumoniae

Question 3

Vector of trench fever is which one of the following?

Accepted Answer

Louse

Answer

Tick

Answer

Mite

Answer

Rat flea

Question 4

Which of the following statements about Streptococcus is false?

Accepted Answer

Group A Streptococcus is catalase positive

Answer

Group B causes neonatal meningitis

Answer

Group B lives in female genital tract

Answer

Classification by Lancefield based on carbohydrate antigen

Bacteriology — MCQs

Bacteriology — MCQs

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