Bacteriology Practice Questions

Q: Pseudomembranous colitis is caused by:

Cl. difficile. ***Clostridium difficile*** - **Pseudomembranous colitis** is a severe inflammation of the colon, most commonly caused by an overgrowth of **Clostridium difficile** bacteria in the gut. - This overgrowth often occurs after antibiotic use, which disrupts the normal gut flora, allowing **C. difficile** to produce toxins that damage the colon lining. *Pseudomonas* - **Pseudomonas aeruginosa** is a common opportunistic pathogen but is not associated with causing **pseudomembranous colitis**. - It is more commonly linked to infections such as hospital-acquired pneumonia, urinary tract infections, and wound infections. *Clostridium welchii* - **Clostridium welchii** is an older name for **Clostridium perfringens**, and it is not the causative agent of **pseudomembranous colitis**. - **Clostridium perfringens** is primarily known for causing **gas gangrene** and a type of **food poisoning**. *Clostridium perfringens* - **Clostridium perfringens** primarily causes **gas gangrene** (a severe soft tissue infection) and certain types of **food poisoning** due to its toxin production. - Unlike **Clostridium difficile**, it does not typically cause **pseudomembranous colitis** following antibiotic use.

Q: Sulfur granules in pus are seen in

Actinomyces israelii. ***Actinomyces israelii*** - **Sulfur granules** are characteristic macroscopic aggregates of filamentous bacteria found in pus from infections caused by *Actinomyces israelii*. - These granules are yellow, gritty, and represent colonies of the organism embedded in a calcium phosphate matrix, indicating an **actinomycosis infection**. *Candida albicans* - *Candida albicans* is a **yeast** that typically causes infections like thrush or candidiasis, which produce creamy white plaques or a curd-like discharge, but not sulfur granules. - It is a **fungus**, not a filamentous bacterium, and its microscopic appearance involves budding yeast cells and pseudohyphae. *Nocardia brasiliensis* - *Nocardia brasiliensis* can cause **nocardiosis**, which may involve cutaneous or pulmonary infections. While it can form granules (mycetoma-like lesions), these are not typically referred to as "sulfur granules" in the same way as *Actinomyces*. - Nocardial infections often present with abscesses and draining sinuses, and its granules are usually smaller and have a different microscopic appearance than those of *Actinomyces*. *Histoplasma capsulatum* - *Histoplasma capsulatum* is a **dimorphic fungus** that causes histoplasmosis, primarily affecting the lungs. - It exists as a mold in the environment and as yeast cells within macrophages in the host; it does not form sulfur granules in pus.

Q: Kallu, a 22 year old male had an outing with his friends and developed fever of 38.50C, diarrhoea, and vomiting following eating chicken salad, 24 hours back. Two of his friends developed the same symptoms. The diagnosis is -

Salmonella enteritis. ***Salmonella enteritis*** - The onset of **fever**, **diarrhea**, and **vomiting** 24 hours after eating potentially contaminated chicken salad, affecting multiple individuals, is highly characteristic of **Salmonella food poisoning** [2], [4]. - **Salmonella enteritidis** is a common cause of foodborne illness associated with poultry and eggs, and causes an **invasive infection** leading to systemic symptoms like fever [2]. *Vibrio cholerae* - **Vibrio cholerae** typically causes profuse, watery diarrhea ("rice-water stools") with severe dehydration, a much shorter incubation period (hours), and less pronounced fever, if any [3]. - It is usually associated with contaminated water sources in endemic areas and not typically isolated cases from common food items like chicken salad. *Bacillus cereus* - **Bacillus cereus** can cause two types of food poisoning: diarrheal (onset 6-15 hours) and emetic (onset 1-6 hours), usually associated with **reheated rice** [1]. - While it causes vomiting and diarrhea, the 24-hour incubation period for the symptoms described makes it less likely, and fever is less prominent than with Salmonella [1], [4]. *S. aureus* - **Staphylococcus aureus** food poisoning typically has a very rapid onset (1-6 hours) after consuming food contaminated with preformed toxins [2], [4]. - Symptoms are predominantly **nausea**, **vomiting**, and abdominal cramps, with diarrhea sometimes present, but fever is uncommon or mild due to the toxin-mediated nature rather than an invasive infection [2].

Q: Causative agents of "Vincent's angina"

Borrelia vincenti and Fusobacterium nucleatum. ***Borrelia vincenti and Fusobacterium nucleatum*** - **Vincent's angina**, also known as **acute necrotizing ulcerative gingivitis (ANUG)**, is polymicrobial and characteristically involves a synergistic infection of **spirochetes** (like *Borrelia vincenti*, now classified as *Treponema vincentii*) and **fusobacteria** (like *Fusobacterium nucleatum*). - These organisms thrive in an anaerobic environment, leading to the characteristic ulcerative and necrotic lesions of the gingiva and oral mucosa. - This synergistic infection produces the classic "fusospirochaetal" complex seen on microscopy. *Borrelia burgdorferi and Lactobacillus* - *Borrelia burgdorferi* is the causative agent of **Lyme disease**, a tick-borne illness causing systemic symptoms, not Vincent's angina. - *Lactobacillus* species are common commensal bacteria found in the oral cavity, gut, and vagina, and are not pathogenic in the context of Vincent's angina. *Leptospira and Treponema pallidum* - *Leptospira* species cause **leptospirosis**, a zoonotic disease with symptoms like fever, headache, and muscle aches, often affecting the kidneys and liver. - *Treponema pallidum* is the causative agent of **syphilis**, a sexually transmitted infection, which presents with different oral lesions (e.g., chancre, mucous patches) that are distinct from Vincent's angina. *Borrelia recurrentis and Bacteroides* - *Borrelia recurrentis* causes **relapsing fever**, characterized by recurrent episodes of fever and other systemic symptoms, transmitted by lice or ticks. - While *Bacteroides* are common anaerobic bacteria in the oral flora, they are not the primary synergistic pair specifically associated with the distinct clinical presentation of Vincent's angina, as are the spirochetes and fusobacteria.

Q: A person returns to Delhi from Bangladesh after 2 days and has diarrhea. Stool examination shows RBC's in stool. The likely organism causing is ?

Shigella dysenteriae. ***Shigella dysenteriae*** - This organism causes **bacillary dysentery**, characterized by fever, abdominal cramps, and frequent, small-volume stools containing **blood and mucus (RBCs)**, which fits the clinical picture of a traveler experiencing diarrhea with RBCs in stool. - The rapid onset (within 2 days of return) and the presence of **RBCs in stool** are highly suggestive of an invasive bacterial pathogen like *Shigella*. *Enteropathogenic E. Coli* - **EPEC** typically causes **watery diarrhea**, particularly in infants, by disrupting intestinal microvilli. - It does **not usually cause bloody stools** or significant red blood cells in the stool. *Salmonella typhi* - While *Salmonella typhi* causes **typhoid fever**, its initial presentation is typically with fever, headache, and constipation, followed by a **pea-soup diarrhea** in later stages, which is usually not bloody. - The rapid onset of bloody diarrhea within 2 days is less characteristic of typhoid fever, which has a longer incubation period. *Enterotoxigenic E. Coli* - **ETEC** is a common cause of **traveler's diarrhea**, but it produces toxins that lead to **watery, non-bloody diarrhea**. - The presence of **RBCs in the stool** makes ETEC an unlikely cause in this scenario.

Q: Regarding Chlamydia infection of the eyes, true statements include the following except:

Penicillin is the treatment. ***Penicillin is the treatment*** - **Penicillin** is ineffective against *Chlamydia trachomatis* because *Chlamydia* lacks a **peptidoglycan cell wall**, which is the target of penicillin. - The standard treatment for chlamydial infections, including ocular infections, involves **azithromycin** or **doxycycline**. *Inclusion conjunctivitis is an acute ocular infection caused by sexually transmitted C. trachomatis strains (usually serovars D through K)* - **Inclusion conjunctivitis** is indeed caused by sexually transmitted serovars of *Chlamydia trachomatis* (typically **D through K**). - It usually occurs in sexually active adults and can affect neonates through maternal transmission. *Can be cultured* - *Chlamydia* are **obligate intracellular bacteria**, meaning they can only replicate inside host cells. - While they can be grown in cell cultures, this is a specialized technique and not a typical method for routine diagnosis due to its complexity and time-consuming nature. *Acute inclusion conjunctivitis typically presents with mucopurulent discharge* - **Acute inclusion conjunctivitis** is characterized by a **mucopurulent discharge**, along with **follicular conjunctivitis** and sometimes **preauricular lymphadenopathy**. - This discharge results from the inflammatory response to the chlamydial infection in the conjunctiva.

Q: All of the following cause Fournier's gangrene except:

Clostridium. ***Clostridium*** - While *Clostridium* species (especially *C. perfringens*) **CAN be isolated** from Fournier's gangrene cases and contribute to gas formation and tissue necrosis, they are **less commonly identified as primary pathogens** compared to other organisms. - In the context of this question, *Clostridium* is considered the "except" option because it is **relatively less frequently implicated** in Fournier's gangrene compared to the other listed organisms, though it is NOT entirely excluded from the microbiology of this condition. - *Clostridium* species are more classically associated with **gas gangrene (clostridial myonecrosis)** in traumatic wounds and deep muscle tissue. *Bacteroides* - ***Bacteroides fragilis*** and other **anaerobic gram-negative bacilli** are among the **most commonly isolated organisms** in Fournier's gangrene. - They produce enzymes that facilitate tissue destruction and contribute significantly to the **polymicrobial synergistic necrotizing infection**. - Essential component of the typical microbial flora in perianal and genital infections. *Streptococcus* - ***Streptococcus pyogenes*** (Group A Streptococcus) and other streptococcal species are **frequently isolated** from Fournier's gangrene. - They produce toxins and enzymes causing **rapid necrotizing fasciitis** with systemic toxicity. - Major contributor to the aggressive nature and rapid progression of the infection. *Staphylococcus* - ***Staphylococcus aureus*** (including MRSA) is **commonly found** in polymicrobial Fournier's gangrene infections. - Contributes to local tissue destruction through toxin production and enzyme activity. - Often isolated from perianal and genital skin flora, facilitating its involvement in these infections.

Q: In children commonest organ involved in nocardiosis is

Lungs. ***Lungs*** - The **lungs** are the primary site of infection for **Nocardia** in both adults and children, as the pathogen is typically acquired via **inhalation**. - **Pulmonary nocardiosis** can manifest as pneumonia, nodules, or cavitary lesions, especially in immunocompromised individuals. *Brain* - While the **brain** can be involved in nocardiosis, leading to **abscesses**, it is usually a result of **hematogenous dissemination** from a primary pulmonary infection, making it a secondary rather than the commonest primary site. - **Cerebral nocardia** is a serious complication, but it does not represent the initial presentation in most cases. *Skin* - **Cutaneous nocardiosis** can occur through direct inoculation into the skin following trauma, but it is less common than pulmonary involvement in children. - Such infections may present as pustules, cellulitis, or subcutaneous abscesses, usually localized to the site of injury. *Renal* - **Renal involvement** in nocardiosis is rare and typically occurs via **hematogenous spread** from a primary site, often the lungs. - It can lead to **renal abscesses** but is not considered a common initial presentation or primary site of infection.

Q: Causative organism of "glanders" is:

Burkholderia mallei. ***Burkholderia mallei*** - **_Burkholderia mallei_** is the bacterial species responsible for causing **glanders**, a contagious disease primarily affecting horses, donkeys, and mules. - Humans can contract glanders through direct contact with infected animals or contaminated materials, with respiratory and cutaneous forms of the disease being common. *Pseudomonas pseudomallei* - **_Pseudomonas pseudomallei_** (`_Burkholderia pseudomallei_`) is the causative agent of **melioidosis**, a severe infection with a wide range of clinical manifestations. - While it's closely related to _Burkholderia mallei_, melioidosis is distinct from glanders and typically found in tropical and subtropical regions. *Leptospira* - **_Leptospira_** is a spirochete bacterium responsible for **leptospirosis**, a zoonotic disease that affects both animals and humans. - It is typically transmitted through contact with water or soil contaminated with the urine of infected animals, presenting with fever, headache, body aches, and sometimes severe organ damage. *Chlamydia* - **_Chlamydia_** is a genus of intracellular bacteria known for causing a variety of infections in humans, including sexually transmitted infections (STIs), eye infections (`_trachoma_`), and respiratory infections. - It is not associated with glanders, which is caused by a distinct bacterial species with a different mode of transmission and host range.

Q: The commonest organism causing Empyema in a child under 2 years -

Pneumococcus. ***Pneumococcus*** - **Streptococcus pneumoniae (Pneumococcus)** is the most common bacterial cause of **empyema** in children across all age groups, including those under 2 years. - It accounts for **40-70% of pediatric empyema cases**, typically developing as a complication of pneumonia. - Even in the post-pneumococcal vaccine era, S. pneumoniae remains the leading cause, though serotype distribution has changed. *Staphylococcus* - **Staphylococcus aureus** is the **second most common** cause of empyema in children under 2 years, accounting for 10-30% of cases. - It causes more severe, rapidly progressing infections with significant **pleural effusion** and **necrotizing pneumonia**. - While historically prominent, it is no longer the most common cause in the modern antibiotic era. *Klebsiella* - **Klebsiella pneumoniae** is a less common cause of empyema in children, more frequently seen in immunocompromised patients or those with underlying chronic diseases. - It is not a typical cause of empyema in otherwise healthy children under 2 years old. *E. Coli* - **Escherichia coli** can cause empyema, particularly in neonates, immunocompromised patients, or as a complication of intra-abdominal infections. - It is a rare cause of empyema in the typical pediatric population under 2 years without specific predisposing factors.

Question 1

Pseudomembranous colitis is caused by:

Accepted Answer

Cl. difficile

Answer

Pseudomonas

Answer

Cl. welchii

Answer

Cl. perfringens

Question 2

Sulfur granules in pus are seen in

Accepted Answer

Actinomyces israelii

Answer

Candida albicans

Answer

Nocardia brasiliensis

Answer

Histoplasma capsulatum

Question 3

Kallu, a 22 year old male had an outing with his friends and developed fever of 38.50C, diarrhoea, and vomiting following eating chicken salad, 24 hours back. Two of his friends developed the same symptoms. The diagnosis is -

Accepted Answer

Salmonella enteritis

Answer

Vibrio cholerae

Answer

Bacillus cereus

Answer

S. aureus

Question 4

Causative agents of "Vincent's angina"

Accepted Answer

Borrelia vincenti and Fusobacterium nucleatum

Answer

Borrelia burgdorferi and Lactobacillus

Answer

Leptospira and Treponema pallidum

Answer

Borrelia recurrentis and Bacteroides

Question 5

A person returns to Delhi from Bangladesh after 2 days and has diarrhea. Stool examination shows RBC's in stool. The likely organism causing is ?

Accepted Answer

Shigella dysenteriae

Answer

Enteropathogenic E. Coli

Answer

Salmonella typhi

Answer

Enterotoxigenic E. Coli

Question 6

Regarding Chlamydia infection of the eyes, true statements include the following except:

Accepted Answer

Penicillin is the treatment

Answer

Inclusion conjunctivitis is an acute ocular infection caused by sexually transmitted C. trachomatis strains (usually serovars D through K)

Answer

Can be cultured

Answer

Acute inclusion conjunctivitis typically presents with mucopurulent discharge

Question 7

All of the following cause Fournier's gangrene except:

Accepted Answer

Clostridium

Answer

Bacteroides

Answer

Streptococcus

Answer

Staphylococcus

Question 8

In children commonest organ involved in nocardiosis is

Accepted Answer

Lungs

Answer

Brain

Answer

Skin

Answer

Renal

Question 9

Causative organism of "glanders" is:

Accepted Answer

Burkholderia mallei

Answer

Pseudomonas pseudomallei

Answer

Leptospira

Answer

Chlamydia

Question 10

The commonest organism causing Empyema in a child under 2 years -

Accepted Answer

Pneumococcus

Answer

Staphylococcus

Answer

Klebsiella

Answer

E.Coli

Bacteriology — MCQs

Bacteriology — MCQs

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