Bacteriology Practice Questions

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.

Q: A 34-year-old man who works as a carpenter presents with symptoms of jaw discomfort, dysphagia, and pain as well as stiffness in his neck, back, and shoulders. On examination, he is unable to open his jaw, his proximal limb muscles are stiff as is his abdomen and back, but the hands and feet are relatively spared. He occasionally has violent generalized muscles spasms that cause him to stop breathing, but there is no loss of consciousness. A clinical diagnosis is made and he is treated with antibiotics, antitoxin, and diazepam as well as muscle relaxants for the spasms.For the above patient, select the most likely infecting organism.

Clostridium tetani. ***Clostridium tetani*** - The patient's symptoms of **jaw discomfort** (lockjaw), **dysphagia**, and **generalized muscle stiffness** with violent spasms, exacerbated by stimuli leading to respiratory compromise, are classic signs of **tetanus** [1]. - **Tetanus** is caused by the neurotoxin **tetanospasmin**, produced by *Clostridium tetani*, which inhibits neurotransmitter release, causing uncontrolled muscle contractions [1]. - Management often includes symptomatic control with diazepam and muscle relaxants to manage convulsions [2]. *Toxoplasma gondii* - This parasite is typically associated with **toxoplasmosis**, which can cause flu-like symptoms, lymphadenopathy, or encephalitis, especially in immunocompromised individuals. - It does not cause the characteristic **spastic paralytic symptoms** and jaw stiffness seen in this patient. *Treponema pallidum* - This bacterium causes **syphilis**, which has various stages presenting with chancres, rashes, or neurological symptoms in later stages (neurosyphilis) [1]. - Its clinical presentation does not involve the acute, severe **muscle spasms** and **trismus** described. *Streptococcus pyogenes* - This bacterium is responsible for infections like strep throat, scarlet fever, and necrotizing fasciitis. - While it can cause severe systemic illness, it does not produce neurotoxins that lead to **spastic paralysis** and lockjaw.

Q: Which of the following is commonly responsible for toxic shock syndrome in female patients:

Staphylococcus aureus. ***Staphylococcus aureus*** - This bacterium produces **TSST-1** (toxic shock syndrome toxin-1), a superantigen that triggers a massive, non-specific T-cell activation and cytokine storm. - The association with **tampon use** in menstruating women and its specific toxins are classic for **toxic shock syndrome**. *Pseudomonas* - While *Pseudomonas aeruginosa* can cause severe infections, it is typically associated with **nosocomial infections**, **cystic fibrosis exacerbations**, or conditions in immunocompromised patients, not classic toxic shock syndrome. - It does not produce the specific superantigens (like TSST-1) linked to the characteristic presentation of toxic shock syndrome. *Streptococcus-group B* - Also known as *Streptococcus agalactiae*, Group B Strep is a common cause of **neonatal sepsis** and **meningitis**, urinary tract infections, and maternal infections during pregnancy. - Group B Streptococcus does **NOT** cause toxic shock syndrome. It is **Group A Streptococcus** (*S. pyogenes*) that causes streptococcal toxic shock syndrome (STSS), typically associated with invasive soft tissue infections. *H.influenzae* - *Haemophilus influenzae* is a significant cause of **otitis media**, **sinusitis**, **epiglottitis**, and **meningitis**, particularly in unvaccinated children. - It is not known to produce the toxins responsible for either staphylococcal or streptococcal toxic shock syndrome.

Q: Acute meningitis in adolescents and young adults is caused by -

N. meningitidis. ***N. meningitidis*** - **_Neisseria meningitidis_** is the most common cause of **bacterial meningitis** in adolescents and young adults, often occurring in outbreaks within close-living communities like dormitories. - It can lead to severe illness, including **sepsis** and **neurological complications**, and rapid diagnosis and treatment are crucial. *H. Influenzae* - **_Haemophilus influenzae_** type b (Hib) was a major cause of bacterial meningitis in **infants and young children** before the widespread introduction of the Hib vaccine. - While it can still cause meningitis particularly in unvaccinated individuals, it is **less common** in adolescents and young adults compared to _N. meningitidis_. *E. coli* - **_Escherichia coli_** is a significant cause of meningitis primarily in **neonates** (newborns), often acquired during passage through the birth canal. - It is **rarely a cause** of meningitis in healthy adolescents and young adults. *Streptococcus* - **_Streptococcus pneumoniae_** (Pneumococcus) and **Group B Streptococcus** (_S. agalactiae_) are important causes of meningitis, but they typically affect different age groups more predominantly. - _S. pneumoniae_ primarily affects **young children and older adults**, while _S. agalactiae_ is a leading cause of **neonatal meningitis**.

Q: A patient presents with vomiting. He had eaten rice 6 hours before. The most probable cause is:

Bacillus cereus. ***Bacillus cereus*** - *Bacillus cereus* is the classic cause of food poisoning associated with **reheated rice**. - The organism produces heat-stable emetic toxin (cereulide) that causes vomiting with an incubation period of **1-6 hours** (typically 2-3 hours). - The combination of **vomiting + rice + 6-hour timeline** makes *B. cereus* the most probable diagnosis. *Staph. aureus* - *Staphylococcus aureus* also causes acute vomiting through preformed enterotoxin with a similar incubation period (30 minutes to 6 hours). - However, *Staph. aureus* food poisoning is more commonly associated with **protein-rich foods** (meat, dairy, custards, cream) rather than rice. - The **specific association with rice** is the key differentiating feature pointing to *Bacillus cereus*. *Cl. difficile* - *Clostridium difficile* causes **antibiotic-associated colitis** and pseudomembranous colitis, not acute food poisoning. - Symptoms primarily include **watery diarrhea, abdominal pain**, and fever, not acute vomiting. - It is NOT transmitted through contaminated food and has a much longer incubation period (days to weeks after antibiotic exposure). *All of the options* - While *Staphylococcus aureus* could theoretically cause vomiting at 6 hours, the rice association strongly favors *Bacillus cereus*. - *Clostridium difficile* is not a cause of acute food poisoning and does not fit this clinical presentation. - Therefore, **Bacillus cereus** is the single most probable cause.

Question 1

Mouse is used for pathogenicity testing in -

Accepted Answer

Bordetella pertussis

Answer

Brucella

Answer

M. Tuberculosis

Answer

C diphtheriae

Question 2

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 3

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 4

Chancroid may be caused by:

Accepted Answer

Haemophilus ducreyi

Answer

Chlamydia Trachomatis

Answer

T. pallidum

Answer

Klebsiella granulomatis

Question 5

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 6

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

Question 7

A 34-year-old man who works as a carpenter presents with symptoms of jaw discomfort, dysphagia, and pain as well as stiffness in his neck, back, and shoulders. On examination, he is unable to open his jaw, his proximal limb muscles are stiff as is his abdomen and back, but the hands and feet are relatively spared. He occasionally has violent generalized muscles spasms that cause him to stop breathing, but there is no loss of consciousness. A clinical diagnosis is made and he is treated with antibiotics, antitoxin, and diazepam as well as muscle relaxants for the spasms.For the above patient, select the most likely infecting organism.

Accepted Answer

Clostridium tetani

Answer

Toxoplasma gondii

Answer

Treponema pallidum

Answer

Streptococcus pyogenes

Question 8

Which of the following is commonly responsible for toxic shock syndrome in female patients:

Accepted Answer

Staphylococcus aureus

Answer

Pseudomonas

Answer

Streptococcus-group B

Answer

H.influenzae

Question 9

Acute meningitis in adolescents and young adults is caused by -

Accepted Answer

N. meningitidis

Answer

H. influenzae

Answer

E. coli

Answer

Streptococcus

Question 10

A patient presents with vomiting. He had eaten rice 6 hours before. The most probable cause is:

Accepted Answer

Bacillus cereus

Answer

Staph. aureus

Answer

Cl. difficile

Answer

All of the options

Bacteriology — MCQs

Bacteriology — MCQs

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