Bacteriology Practice Questions

Q: HP bodies (Halberstaedter-Prowazek bodies) are seen in infections caused by which organism?

Chlamydia trachomatis. ***Chlamydia trachomatis*** - **Halberstaedter-Prowazek (HP) bodies** are distinctive **intracytoplasmic inclusions** found in the host cells infected with **Chlamydia trachomatis**. - These inclusions contain replicating **reticulate bodies** and are characteristic of this species. - A key feature is that HP bodies are **glycogen-rich** and **stain with iodine** (iodine-positive), which is a pathognomonic diagnostic feature distinguishing *C. trachomatis* from other Chlamydia species. *Chlamydia psittaci* - While *Chlamydia psittaci* also forms inclusions, they are generally **larger**, **less compact**, and **iodine-negative** (do not contain glycogen) compared to the HP bodies seen in *C. trachomatis*. - *C. psittaci* is primarily associated with **psittacosis**, a respiratory disease transmitted from birds. *Mycoplasma hominis* - *Mycoplasma* species are **wall-less bacteria** and do not form **intracytoplasmic inclusions** like Chlamydia. - They are distinct from Chlamydia in their cellular structure and life cycle. *Chlamydia pneumoniae* - *Chlamydia pneumoniae* forms **inclusions** that are **iodine-negative** (lack glycogen), **pear-shaped**, and morphologically different from the classical compact HP bodies. - This species is a common cause of **atypical pneumonia** and lacks the distinctive cytological features of *C. trachomatis* inclusions.

Q: A 20-year-old man presents with dysuria, urgency, and urethral discharge. Physical examination shows suppurative urethritis, with redness and swelling at the urethral meatus. Which of the following is the most likely etiology of urethritis in this patient?

Neisseria gonorrhoeae. ***Neisseria gonorrhoeae*** - The presentation of **dysuria, urgency, urethral discharge**, and **suppurative urethritis** (purulent discharge with redness and swelling) is highly characteristic of **gonococcal urethritis** [1]. - **Gonorrhea** is a common cause of sexually transmitted urethritis, especially with prominent inflammatory signs [1]. *Haemophilus ducreyi* - This bacterium is the causative agent of **chancroid**, which typically presents as painful genital ulcers with regional lymphadenopathy. - It does not cause urethritis with significant urethral discharge as described. *Chlamydia trachomatis* - While *Chlamydia trachomatis* is a common cause of urethritis, it typically causes **non-gonococcal urethritis (NGU)**, which is often less symptomatic and may present with a thinner, mucoid discharge [1]. - The **suppurative (purulent) nature** of the discharge described points more strongly towards gonorrhea [1]. *Ureaplasma urealyticum* - *Ureaplasma urealyticum* is a known cause of **non-chlamydial, non-gonococcal urethritis**, similarly to *Chlamydia* [1]. - However, its presentation is generally milder and less suppurative than that caused by *Neisseria gonorrhoeae* [1].

Q: Which organism causes prosthetic valve endocarditis within 60 days of surgery?

Staphylococcus epidermidis. ***Staphylococcus epidermidis*** - This organism is the **most common cause of early prosthetic valve endocarditis (within 60 days of surgery)**, accounting for 30-40% of cases. - As a coagulase-negative Staphylococcus, *S. epidermidis* commonly colonizes the skin and can be introduced during the surgical procedure. - It produces **biofilms**, which allow it to adhere to prosthetic surfaces and resist antibiotic treatment. *Staphylococcus aureus* - *Staphylococcus aureus* is the **second most common cause of early prosthetic valve endocarditis** (20-25% of cases) and can cause both early and late infections. - It typically presents with a more **fulminant, aggressive course** compared to *S. epidermidis*. - While both staphylococcal species cause early PVE, *S. epidermidis* remains more frequent. *Fungus* - **Fungal endocarditis** on prosthetic valves (typically *Candida* species) accounts for 5-10% of early PVE cases. - More commonly seen in immunocompromised patients, those with prolonged antibiotic use, or after complicated cardiac surgery. - Its incidence is significantly lower than staphylococcal causes in the early post-operative period. *Streptococcus viridans* - *Streptococcus viridans* is the **most common cause of native valve endocarditis**, particularly in patients with pre-existing valvular heart disease. - It typically causes a **subacute presentation** and is more associated with **late prosthetic valve endocarditis** (>60 days post-surgery), not early PVE. - Rarely implicated in early prosthetic valve infections.

Q: In which year was Helicobacter pylori identified?

1983. ***1983*** - **Barry Marshall** and **Robin Warren** successfully cultured *Helicobacter pylori* from stomach biopsies, challenging the long-held belief that bacteria could not survive in the acidic environment of the stomach. - Their work definitively linked the bacterium to **gastritis** and **peptic ulcers**, revolutionizing understanding and treatment of these conditions. *1976* - This year is not recognized for the identification or significant discovery of *Helicobacter pylori*. - While research into stomach health was ongoing, the specific identification of this bacterium occurred later. *1994* - By 1994, *Helicobacter pylori* was well-established as a major pathogen, and this year saw significant progress in understanding its role in **gastric cancer**, leading to its classification as a Group 1 carcinogen by the WHO. - However, its *identification* happened much earlier. *1969* - Although there were earlier observations of spiral-shaped bacteria in the stomach, particularly by **Waldo L. Stewart** in 1969, these initial findings did not lead to the successful culture and definitive identification of *Helicobacter pylori* as a pathogenic agent. - The crucial link to gastric disease was not established at this time.

Q: Mouse is used for pathogenicity testing in -

Bordetella pertussis. **Bordetella pertussis** - Mice are commonly used as an animal model for studying the **pathogenesis of pertussis** and for testing vaccine efficacy. - They allow researchers to observe the **infection's progression** in a living system and evaluate potential treatments. *Brucella* - While animal models are used for *Brucella* research, typically **guinea pigs or cattle** are preferred for pathogenicity testing due to their susceptibility and similarity to natural hosts. - Mice can be infected, but they are not the primary model for assessing *Brucella* virulence in the same way they are for *Bordetella pertussis*. *M. Tuberculosis* - **Guinea pigs** are classically used for pathogenicity testing of *Mycobacterium tuberculosis* due to their high susceptibility and ability to develop **granulomatous lesions** similar to humans. - While mice can be infected, guinea pigs are preferred for assessing virulence and vaccine efficacy in a model that closely mimics human disease. *C diphtheriae* - **Guinea pigs** are the standard animal model for testing the **toxigenicity of *Corynebacterium diphtheriae*** strains, often through the Elek test or in vivo challenge. - Mice are generally less susceptible to diphtheria toxin and are not routinely used for this specific pathogenicity test.

Q: True about Trench fever are all except -

Doxycycline is the treatment. ***Doxycycline is the treatment*** - While **doxycycline** can be used as an alternative, the primary and most effective treatment for trench fever is **azithromycin**. - **Relapse** is common in trench fever due to the **intracellular nature** of *Bartonella quintana*, requiring prolonged or repeated treatment courses. *Transmitted by Pediculus corporis* - Trench fever is indeed transmitted by the **human body louse**, *Pediculus humanus corporis*, which acquires the bacteria from an infected person's blood. - The louse then excretes infected feces, which can be rubbed into the skin through scratching or enter through mucous membranes. *Caused by Bartonella quintana* - The etiologic agent of trench fever is **Bartonella quintana**, a **Gram-negative bacterium**. - This bacterium is an **intracellular pathogen** that primarily infects **erythrocytes** and **endothelial cells**. *Also called 7-day fever* - Trench fever is also known as "5-day fever" or "shin bone fever" due to the characteristic **recurrent fever pattern** that typically recurs every five days. - The term "7-day fever" is more commonly associated with illnesses like **dengue fever** or **leptospirosis**, not trench fever.

Q: Vibrio parahemolyticus food poisoning is caused by ingestion of -

Seafood (shellfish, fish). ***Seafood (shellfish, fish)*** - **Vibrio parahemolyticus** is a **halophilic bacterium** (salt-loving) commonly found in **marine environments** and associated with **raw or undercooked seafood**. - Ingestion of contaminated seafood, such as **shellfish, fish, and other marine products**, is the primary mode of transmission for **Vibrio parahemolyticus food poisoning**. - Common sources include oysters, shrimp, crabs, and fish from coastal waters. *Milk products* - **Milk products** are not typically associated with **Vibrio parahemolyticus** infections, as this bacterium thrives in saline, marine environments. - Contamination of milk products leading to bacterial gastroenteritis is more commonly linked to organisms like *Salmonella*, *Campylobacter*, or *Listeria*. *Raw vegetables* - **Raw vegetables** are generally not a significant source of **Vibrio parahemolyticus**, which is predominantly found in **seafood**. - Contamination of vegetables can occur with other bacteria like *E. coli* or *Salmonella*, especially if irrigated with contaminated water. *Eggs and Poultry products* - **Eggs and poultry products** are known sources of bacterial food poisoning, most notably from *Salmonella* species if not cooked properly. - They are not typically associated with **Vibrio parahemolyticus**, which thrives in saltwater environments.

Q: Chancroid may be caused by:

Haemophilus ducreyi. ***Haemophilus ducreyi*** - **Chancroid** is a sexually transmitted infection characterized by painful genital ulcers and regional lymphadenopathy, and its causative agent is **Haemophilus ducreyi**. - This bacterium is a **Gram-negative coccobacillus** that leads to the formation of soft chancres. *Chlamydia Trachomatis* - **Chlamydia trachomatis** is responsible for **chlamydia**, a common STI that can cause urethritis, cervicitis, and lymphogranuloma venereum (LGV), but not chancroid. - LGV involves significant **lymph node enlargement** and draining sinuses, distinct from the typical chancres of chancroid. *T. pallidum* - **Treponema pallidum** is the spirochete responsible for **syphilis**, which presents with a painless chancre in its primary stage. - Unlike chancroid, the **syphilitic chancre** is typically firm, clean-based, and usually solitary. *G. donovani* - **Klebsiella granulomatis (formerly Calymmatobacterium granulomatis)** is the causative agent of **granuloma inguinale (donovanosis)**, another STI. - Granuloma inguinale presents with progressive, painless, beefy-red ulcerative lesions that bleed easily, which are distinct from the painful ulcers of chancroid.

Q: Most common bacteria responsible for the condition shown in the image below in a child who presents with high grade fever and sore throat is?

Group A streptococcus. ***Group A streptococcus*** - This symptom complex (high fever and sore throat) in a child strongly suggests **streptococcal pharyngitis**, commonly caused by **Group A Streptococcus (GAS)**, specifically *Streptococcus pyogenes*. - Untreated **GAS pharyngitis** can lead to serious complications such as **rheumatic fever** or **post-streptococcal glomerulonephritis**. *Group B streptococcus* - **Group B Streptococcus (GBS)** is primarily known to cause **neonatal infections** (e.g., sepsis, meningitis) due to vertical transmission from mother to infant. - While GBS can cause infections in older children and adults, it is not a common cause of typical **pharyngitis** with high fever and sore throat in children. *Staphylococcus aureus* - *Staphylococcus aureus* commonly causes **skin and soft tissue infections** (e.g., impetigo, cellulitis, abscesses) and can cause more severe conditions like pneumonia or sepsis. - It is not a common or typical cause of primary **pharyngitis** with fever and sore throat in otherwise healthy children. *Corynebacterium diphtheria* - **Corynebacterium diphtheriae** causes **diphtheria**, characterized by a **pseudomembrane** formation in the throat, which can lead to airway obstruction and systemic toxicity. - While it presents with sore throat and fever, **diphtheria** is rare in developed countries due to widespread vaccination and the clinical features are usually more severe and distinct than typical strep throat.

Q: Most common agent causing tuberculosis in AIDS patients in tropical countries is:

Mycobacterium tuberculosis. ***Mycobacterium tuberculosis*** - Despite immune compromise, **classical *Mycobacterium tuberculosis* (MTB)** remains the most common cause of tuberculosis in AIDS patients globally, including in tropical regions. - The high prevalence of **latent TB infection** in these populations, coupled with HIV-induced immunosuppression, leads to reactivation of MTB as the primary pathology. *Atypical mycobacteria* - While atypical mycobacteria can cause disseminated disease in AIDS patients, they are generally **less common** than *Mycobacterium tuberculosis* in causing true tuberculosis in tropical countries. - Atypical mycobacterial infections typically occur in patients with **more severe immunosuppression** (lower CD4 counts) than those with primary pulmonary TB caused by M. tuberculosis. *Mycobacterium intracellulare* - *Mycobacterium intracellulare* is a species of **atypical mycobacteria** often grouped with *Mycobacterium avium* as MAC. - Although it causes disseminated disease in AIDS patients, it is not the most common agent of tuberculosis compared to *Mycobacterium tuberculosis*. *Mycobacterium avium* - *Mycobacterium avium*, part of the **Mycobacterium Avium Complex (MAC)**, frequently causes disseminated infection in AIDS patients, especially with **CD4 counts below 50 cells/mm³**. - However, it typically manifests as a **disseminated disease** rather than classic pulmonary tuberculosis, and is overall less common than *Mycobacterium tuberculosis* as the causative agent of TB in tropical settings.

Question 1

HP bodies (Halberstaedter-Prowazek bodies) are seen in infections caused by which organism?

Accepted Answer

Chlamydia trachomatis

Answer

Chlamydia psittaci

Answer

Mycoplasma hominis

Answer

Chlamydia pneumoniae

Question 2

A 20-year-old man presents with dysuria, urgency, and urethral discharge. Physical examination shows suppurative urethritis, with redness and swelling at the urethral meatus. Which of the following is the most likely etiology of urethritis in this patient?

Accepted Answer

Neisseria gonorrhoeae

Answer

Haemophilus ducreyi

Answer

Chlamydia trachomatis

Answer

Ureaplasma urealyticum

Question 3

Which organism causes prosthetic valve endocarditis within 60 days of surgery?

Accepted Answer

Staphylococcus epidermidis

Answer

Staphylococcus aureus

Answer

Fungus

Answer

Streptococcus viridans

Question 4

In which year was Helicobacter pylori identified?

Accepted Answer

1983

Answer

1976

Answer

1994

Answer

1969

Question 5

Mouse is used for pathogenicity testing in -

Accepted Answer

Bordetella pertussis

Answer

Brucella

Answer

M. Tuberculosis

Answer

C diphtheriae

Question 6

True about Trench fever are all except -

Accepted Answer

Doxycycline is the treatment

Answer

Transmitted by Pediculus corporis

Answer

Caused by Bartonella quintana

Answer

Also called 7-day fever

Question 7

Vibrio parahemolyticus food poisoning is caused by ingestion of -

Accepted Answer

Seafood (shellfish, fish)

Answer

Milk products

Answer

Raw vegetables

Answer

Eggs and Poultry products

Question 8

Chancroid may be caused by:

Accepted Answer

Haemophilus ducreyi

Answer

Chlamydia Trachomatis

Answer

T. pallidum

Answer

Klebsiella granulomatis

Question 9

Most common bacteria responsible for the condition shown in the image below in a child who presents with high grade fever and sore throat is?

Accepted Answer

Group A streptococcus

Answer

Group B streptococcus

Answer

Staphylococcus aureus

Answer

Corynebacterium diphtheriae

Question 10

Most common agent causing tuberculosis in AIDS patients in tropical countries is:

Accepted Answer

Mycobacterium tuberculosis

Answer

Atypical mycobacteria

Answer

Mycobacterium intracellulare

Answer

Mycobacterium avium

Bacteriology — MCQs

Bacteriology — MCQs

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