Bacteriology Practice Questions

Q: Species of Shigella most commonly causing arthritis

Shigella flexneri. ***Shigella flexneri*** - This species is most commonly associated with **post-infectious reactive arthritis**, especially in individuals with the **HLA-B27 genotype**. - The arthritis typically develops days to weeks after the diarrheal illness and can affect large joints. *Shigella boydii* - While *Shigella boydii* can cause **shigellosis**, it is less frequently implicated in reactive arthritis compared to *Shigella flexneri*. - Its infections are more common in some developing regions but have a lower association with rheumatological sequelae. *Shigella dysenteriae* - *Shigella dysenteriae* causes severe forms of shigellosis, including **dysentery with potential hemolytic-uremic syndrome**, particularly serotype 1. - Although it can trigger reactive arthritis, its prevalence as a cause of this complication is lower than *Shigella flexneri*. *Shigella sonnei* - *Shigella sonnei* is the most common cause of **shigellosis in industrialized countries** and often presents with milder symptoms. - While reactive arthritis can theoretically follow any *Shigella* infection, *S. sonnei* is less commonly linked to this specific complication compared to *S. flexneri*.

Q: Clinical classification of staphylococcus is based on -

Coagulase test. ***Coagulase test*** - The **coagulase test** is the primary method used to differentiate pathogenic *Staphylococcus aureus* from non-pathogenic coagulase-negative staphylococci. - *S. aureus* produces **coagulase**, an enzyme that clots plasma, while other staphylococci do not. *Catalase test* - The **catalase test** differentiates staphylococci from streptococci (staphylococci are catalase-positive, streptococci are catalase-negative). - It does not help in differentiating between different *Staphylococcus* species. *Mannitol fermentation* - **Mannitol fermentation** is a characteristic used to distinguish *Staphylococcus aureus* (ferments mannitol) from some other *Staphylococcus* species (e.g., *Staphylococcus epidermidis*). - While helpful, it is not the primary test for broad classification of the genus. *Optochin sensitivity* - **Optochin sensitivity** is a test used to identify *Streptococcus pneumoniae* (sensitive) from other alpha-hemolytic streptococci. - This test is not used for the classification or differentiation of *Staphylococcus* species.

Q: What is the causative agent of erythrasma?

Corynebacterium. ***Corynebacterium*** - **Erythrasma** is a superficial skin infection caused by a specific species of bacteria, **Corynebacterium minutissimum**. - This bacterium produces **porphyrins** that fluoresce a distinctive coral-red color under a Wood's lamp, aiding in diagnosis. *Staphylococcus* - **Staphylococcus aureus** is a common cause of various skin infections such as **impetigo**, **folliculitis**, and **boils**, but not erythrasma. - These infections typically present with **pus-filled lesions** or crusting. *Streptococcus* - **Streptococcus pyogenes** is known to cause **erysipelas** and **cellulitis**, which are characterized by rapidly spreading red, warm, and tender skin. - It is also a causative agent of **impetigo**, but not erythrasma. *Herpes Virus* - Herpes viruses, such as **Herpes Simplex Virus (HSV)**, cause **cold sores** and **genital herpes**, manifesting as painful blisters. - They are **viruses**, not bacteria, and do not cause erythrasma.

Q: Pseudo-hemoptysis is seen mostly with

Serratia marcescens. ***Serratia marcescens*** - This bacterium is well-known for producing a distinctive **red pigment**, **prodigiosin**, which can cause sputum to appear blood-tinged. - This pigment can lead to a false impression of **hemoptysis (pseudo-hemoptysis)**, particularly in patients with respiratory infections caused by this organism. *Streptococcus pneumoniae* - While a common cause of pneumonia, it typically causes **rust-colored sputum** due to the presence of blood and inflammatory cells, but not a vivid red pigment that mimics fresh blood. - This organism is more commonly associated with **frank hemoptysis** or purulent sputum, rather than pseudo-hemoptysis caused by pigment. *Escherichia coli* - Primarily a **gastrointestinal pathogen**, *E. coli* rarely causes respiratory infections, and when it does, it does not produce a red pigment in sputum. - It is not known to cause pseudo-hemoptysis; its presence in sputum would indicate a severe systemic infection or aspiration. *Respiratory Syncytial Virus (RSV)* - RSV is a common cause of **viral respiratory infections**, especially in children, and is associated with clear or whitish nasal secretions and cough. - It does not cause the production of pigmented sputum, nor does it typically lead to hemoptysis or pseudo-hemoptysis.

Q: Which of the following organisms is known to cause atrophic rhinitis?

Klebsiella ozaenae. ***Klebsiella ozaenae*** - *Klebsiella ozaenae* is the organism most commonly associated with **primary atrophic rhinitis**, also known as **ozena**. - It produces characteristic **foul-smelling crusts** in the nasal cavity due to its metabolic byproducts. *Streptococcus pneumoniae* - *Streptococcus pneumoniae* is a common cause of **bacterial sinusitis** and **otitis media**, but not atrophic rhinitis. - It typically causes acute infections rather than chronic atrophic changes. *Streptococcus foetidus* - *Streptococcus foetidus* is a less common organism and is not a known primary cause of **atrophic rhinitis**. - It is more often associated with infections like **abscesses** or **postoperative complications**. *Klebsiella pneumoniae* - *Klebsiella pneumoniae* is a significant pathogen causing **pneumonia**, **urinary tract infections**, and **hospital-acquired infections**. - While it belongs to the same genus as *K. ozaenae*, it is not specifically implicated in **atrophic rhinitis**.

Q: Which of the following Staphylococcal infections is not primarily toxin-mediated?

Septic shock. ***Septic shock*** - Septic shock is primarily mediated by the **host's inflammatory response** to bacteria (or their components like **LPS** in Gram-negative bacteria, or **peptidoglycan** and **teichoic acid** in Gram-positive bacteria, like *Staphylococcus*), rather than by a specific bacterial toxin. - The systemic inflammatory response can lead to widespread **vasodilation**, capillary leak, and **organ dysfunction**, commonly seen in severe infections like **bacteremia** with *Staphylococcus aureus*. *Toxic shock syndrome* - This condition is caused by **superantigen toxins** like **TSST-1** (Toxic Shock Syndrome Toxin-1) produced by certain strains of *Staphylococcus aureus*, leading to massive **T cell activation** and cytokine release. - It presents with sudden onset of **fever**, **hypotension**, diffuse erythematous rash, and **multisystem organ involvement**, distinguishing it from septic shock primarily driven by host immune response. *Scalded skin syndrome* - This syndrome is caused by **exfoliative toxins (ETA and ETB)** produced by *Staphylococcus aureus*, which target **desmoglein 1** in the skin, leading to widespread **epidermal exfoliation** and Nikolsky's sign. - The toxins cause the distinct blistering and peeling of the skin, making it a classic example of a **toxin-mediated dermopathy**. *Food poisoning* - *Staphylococcal* food poisoning is mediated by **heat-stable enterotoxins (e.g., SEA, SEB)** produced by *Staphylococcus aureus* growing in contaminated food. - Symptoms like **nausea**, **vomiting**, and **diarrhea** occur rapidly after ingestion, as preformed toxins directly stimulate the **vagal nerves** in the gastrointestinal tract.

Q: Subterminal spores are seen in which of the following organisms?

Clostridium perfringens. ***Clostridium perfringens*** - This bacterium is known for producing **subterminal spores**, meaning the spores are located near, but not at, the end of the cell. - *C. perfringens* is a common cause of **gas gangrene** and food poisoning, often forming spores under adverse environmental conditions. *Clostridium tetani* - *C. tetani* produces **terminal spores**, which are found directly at one end of the bacterial cell. - These terminal spores give the organism a characteristic **"drumstick" or "tennis racket" appearance**. *Clostridium tertium* - Similar to *Clostridium tetani*, *C. tertium* is also known to produce **terminal spores**. - Its spores are typically located at the extreme end of the cell. *None of the options* - This option is incorrect because *Clostridium perfringens* specifically fits the description of producing subterminal spores. - The other *Clostridium* species listed, *C. tetani* and *C. tertium*, produce terminal spores, not subterminal.

Q: LGV (lymphogranuloma venereum) is caused by?

Chlamydia trachomatis. ***Correct: Chlamydia trachomatis*** - **Lymphogranuloma venereum (LGV)** is a sexually transmitted infection caused by specific serovars (**L1, L2, L3**) of *Chlamydia trachomatis* - These serovars are **invasive** and replicate in **mononuclear phagocytes** in regional lymph nodes - LGV presents with **painless genital ulcer** followed by **painful inguinal lymphadenopathy** (buboes) *Incorrect: Calymmatobacter granulomatis* - This bacterium causes **granuloma inguinale** (donovanosis), not LGV - Characterized by **painless, progressive ulcerative lesions** without prominent lymphadenopathy - Diagnosis shows **Donovan bodies** on tissue smear *Incorrect: Haemophilus ducreyi* - *H. ducreyi* causes **chancroid**, not LGV - Presents with **painful genital ulcers** and **suppurative inguinal lymphadenitis** - Key difference: painful ulcers (vs painless in LGV primary lesion) *Incorrect: Treponema pallidum* - *T. pallidum* causes **syphilis**, not LGV - Primary syphilis presents with **painless chancre** with firm borders - Lymphadenopathy is bilateral, firm, and non-tender (different from LGV buboes)

Q: Which of the following statements about diphtheria toxin is true?

It consists of two fragments.. ***It consists of two fragments.*** - Diphtheria toxin is a **protein exotoxin** composed of an **A subunit (active)** and a **B subunit (binding)**, connected by a disulfide bond. - The **A subunit** inhibits protein synthesis by ADP-ribosylation of elongation factor-2 (EF-2), while the **B subunit** facilitates binding and entry into host cells. - This two-fragment structure is the **classic and most characteristic feature** of diphtheria toxin. *It is heat labile.* - While diphtheria toxin can be inactivated by heating at high temperatures (60°C for 10 minutes), it is relatively **more stable** compared to many other bacterial toxins under moderate conditions. - The **two-fragment structure** is considered the more definitively characteristic feature for exam purposes. *It acts through cGMP.* - Diphtheria toxin's mechanism of action involves **ADP-ribosylation of elongation factor-2 (EF-2)**, which inhibits host protein synthesis. - It does not exert its effects through the **cGMP signaling pathway** (cholera toxin acts through cAMP). *It has a special affinity for the brain.* - Diphtheria toxin primarily affects tissues with high protein synthesis turnover, such as the **heart (myocarditis)** and **nerves (peripheral neuropathy)**, rather than the brain. - Neurological complications are typically **peripheral neuropathies**, not central nervous system effects.

Q: Primary mode of transmission of Listeria monocytogenes is:

Ingestion. ***Ingestion*** - *Listeria monocytogenes* is primarily transmitted through the **consumption of contaminated food**, making **ingestion** the main route. - This bacterium can adapt well to cold temperatures and grow in refrigerated foods, such as **deli meats**, **soft cheeses**, and **unpasteurized milk**. *Inhalation* - While possible in specific occupational settings (e.g., slaughterhouse workers exposed to aerosols), **inhalation** is not the primary mode of transmission for the general population. - Respiratory infections with *Listeria* are rare and typically occur secondary to severe systemic infection. *Skin inoculation* - **Skin inoculation** is an uncommon route of transmission for *Listeria monocytogenes* and is not considered a primary mode of spread. - It could theoretically occur through direct contact with infected animal tissues, but this is a rare event. *None of the options* - This option is incorrect because **ingestion** is a well-established and primary mode of transmission for *Listeria monocytogenes*. - The other options are either rare or not the main way this pathogen is acquired by humans.

Question 1

Species of Shigella most commonly causing arthritis

Accepted Answer

Shigella flexneri

Answer

Shigella boydii

Answer

Shigella dysenteriae

Answer

Shigella sonnei

Question 2

Clinical classification of staphylococcus is based on -

Accepted Answer

Coagulase test

Answer

Catalase test

Answer

Mannitol fermentation

Answer

Optochin sensitivity

Question 3

What is the causative agent of erythrasma?

Accepted Answer

Corynebacterium

Answer

Staphylococcus

Answer

Streptococcus

Answer

Herpes Virus

Question 4

Pseudo-hemoptysis is seen mostly with

Accepted Answer

Serratia marcescens

Answer

Escherichia coli

Answer

Respiratory Syncytial Virus (RSV)

Answer

Streptococcus pneumoniae

Question 5

Which of the following organisms is known to cause atrophic rhinitis?

Accepted Answer

Klebsiella ozaenae

Answer

Streptococcus foetidus

Answer

Streptococcus pneumoniae

Answer

Klebsiella pneumoniae

Question 6

Which of the following Staphylococcal infections is not primarily toxin-mediated?

Accepted Answer

Septic shock

Answer

Toxic shock syndrome

Answer

Scalded skin syndrome

Answer

Food poisoning

Question 7

Subterminal spores are seen in which of the following organisms?

Accepted Answer

Clostridium perfringens

Answer

Clostridium tetani

Answer

Clostridium tertium

Answer

None of the options

Question 8

LGV (lymphogranuloma venereum) is caused by?

Accepted Answer

Chlamydia trachomatis

Answer

Calymmatobacter granulomatis

Answer

Haemophilus ducreyi

Answer

Treponema pallidum

Question 9

Which of the following statements about diphtheria toxin is true?

Accepted Answer

It consists of two fragments.

Answer

It is heat labile.

Answer

It acts through cGMP.

Answer

It has a special affinity for the brain.

Question 10

Primary mode of transmission of Listeria monocytogenes is:

Accepted Answer

Ingestion

Answer

Inhalation

Answer

Skin inoculation

Answer

None of the options

Bacteriology — MCQs

Bacteriology — MCQs

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