Bacteriology Practice Questions

Q: Whipple's disease is caused by:

Bacteria. **Bacteria** - Whipple's disease is caused by the bacterium **_Tropheryma whipplei_**, a rod-shaped, gram-positive actinobacterium. - This bacterium causes a chronic, systemic infection affecting various organ systems, most commonly the gastrointestinal tract. *Virus* - Viruses are intracellular parasites that reproduce inside living cells, and they are not the causative agent of Whipple's disease. - While viral infections can cause gastrointestinal symptoms, they do not lead to the distinct histopathological findings of Whipple's disease, such as **PAS-positive macrophages**. *Helminths* - Helminths are parasitic worms (e.g., tapeworms, roundworms) that can cause intestinal and systemic infections. - These organisms are multicellular eukaryotes and are distinct from the bacterial etiology of Whipple's disease. *Protozoa* - Protozoa are single-celled eukaryotic organisms that can cause a range of infections, often gastrointestinal (e.g., Giardia, Entamoeba). - While parasitic infections can cause malabsorption, the specific **PAS-positive macrophage infiltrates** seen in Whipple's disease are characteristic of bacterial infection, not protozoan.

Q: What is the causative agent for malignant otitis externa?

Pseudomonas. ***Pseudomonas*** - **Malignant otitis externa** is a severe, rapidly progressive infection of the external auditory canal and skull base, primarily caused by **Pseudomonas aeruginosa**. - This opportunistic bacterium thrives in moist environments and commonly affects immunocompromised individuals, such as diabetics or the elderly. *Streptococcus* - While various *Streptococcus* species can cause common ear infections (e.g., **otitis media**), they are not the primary causative agent for malignant otitis externa. - Infections by *Streptococcus* typically present differently and affect other parts of the ear or body more commonly. *Staphylococcus aureus* - **Staphylococcus aureus** is a common cause of skin infections, including localized forms of otitis externa (e.g., furuncles), but it is rarely implicated in the aggressive, invasive form known as malignant otitis externa. - When *Staphylococcus aureus* is involved, it often presents differently and is less likely to cause skull base osteomyelitis. *Influenza* - **Influenza** is a viral infection primarily affecting the **respiratory system** and is not a bacterial pathogen responsible for otitis externa, malignant or otherwise. - Viral infections like influenza can predispose individuals to secondary bacterial infections, but they are not directly causative of this condition.

Q: Bacterial vaginosis is caused by all except

Proteus. ***Proteus*** - **Proteus** species are commonly associated with **urinary tract infections (UTIs)** and wound infections, not typically with bacterial vaginosis. - The presence of **Proteus** in vaginal flora is generally considered an opportunistic infection rather than a causative agent of BV. *Coccobacillus* - **Coccobacillary bacteria**, such as **Gardnerella vaginalis**, are primary organisms contributing to the polymicrobial shift that defines bacterial vaginosis. - The disruption of normal lactobacilli dominance allows for the overgrowth of these specific anaerobic and facultative organisms. *Mobiluncus* - **Mobiluncus species** are curved, rod-shaped anaerobic bacteria frequently found in high numbers in women with bacterial vaginosis. - They are considered key anaerobic bacteria involved in the microbial imbalance characteristic of BV. *Gardnerella* - **Gardnerella vaginalis** is the most commonly isolated bacterium in bacterial vaginosis and is considered the primary initiating organism. - While BV is polymicrobial, **Gardnerella's** overgrowth is central to the diagnostic criteria and pathogenesis.

Q: Most common cause of bacterial meningitis in post-neonatal period:

Streptococcus pneumoniae. ***Streptococcus pneumoniae*** - *S. pneumoniae* is the most common cause of **bacterial meningitis** in the post-neonatal period (1 month to 1 year of age), particularly in regions with high vaccination rates against Hib. - Its polysaccharide capsule and ability to evade the immune system contribute to its virulence in causing **central nervous system infections**. - Accounts for approximately 40-50% of bacterial meningitis cases in this age group. *Mycobacterium tuberculosis* - While it can cause **tuberculous meningitis**, this is a less common form of meningitis, typically with a more **insidious onset** and often associated with immunosuppression or endemic areas. - Represents a chronic form of meningitis rather than acute bacterial meningitis. *Staphylococcus aureus* - *S. aureus* meningitis typically occurs in specific contexts such as **post-neurosurgery**, following head trauma, or in patients with indwelling catheters or bacteremia. - It is not the most frequent pathogen in community-acquired meningitis in infants. *Klebsiella* - **Klebsiella pneumoniae** can cause meningitis, especially in **neonates** (first 28 days of life), immunocompromised individuals, or patients with healthcare-associated infections. - However, it is not the most common cause of meningitis in the post-neonatal period.

Q: Bacillus anthracis is:

Gram positive rods with square ends. ***Gram positive rods with square ends*** - *Bacillus anthracis* is a **gram-positive bacterium**, meaning it retains the crystal violet stain due to its thick peptidoglycan layer. - Microscopically, it appears as **large, rod-shaped bacteria** (bacilli) with characteristic **square-cut ends**, often arranged in chains. *Gram negative cocci in cluster* - This describes organisms like **Neisseria gonorrhoeae** or **meningitidis**, which are spherical (cocci) and appear pink/red after Gram staining. - *Bacillus anthracis* is a **rod-shaped bacterium** that stains Gram-positive. *Gram positive cocci in cluster* - This morphology is characteristic of **Staphylococcus species**, which are spherical bacteria that stain purple and arrange in grape-like clusters. - *Bacillus anthracis* is a **rod-shaped bacterium**, not a coccus. *Gram positive bacilli with spherical ends* - While *Bacillus anthracis* is a **gram-positive bacillus**, its ends are distinctly **square-cut**, not spherical. - Bacteria with spherical or rounded ends would include some other *Bacillus* species or members of the **Clostridium** genus.

Q: The causative agent for duodenal ulcer is:

H. Pylori. ***H. pylori*** - ***H. pylori*** is a **Gram-negative spiral-shaped bacterium** that colonizes the stomach and duodenum, causing inflammation and increasing the risk of peptic ulcers, including duodenal ulcers. - It produces **urease**, which neutralizes stomach acid by converting urea to ammonia, protecting the bacteria and contributing to mucosal damage. *Lactobacilli* - **Lactobacilli** are **Gram-positive, rod-shaped bacteria** commonly found in the digestive tract and fermented foods. - They are generally considered **beneficial probiotics** and do not cause duodenal ulcers. *E. coli* - ***E. coli*** is a **Gram-negative, rod-shaped bacterium** typically found in the intestines of humans and animals. - While some strains can cause **gastrointestinal infections** (e.g., traveler's diarrhea), *E. coli* is not a known cause of duodenal ulcers. *Shigella* - **Shigella** is a **Gram-negative, rod-shaped bacterium** that causes **shigellosis**, an intestinal infection characterized by severe diarrhea (dysentery). - It primarily affects the **large intestine** and does not cause duodenal ulcers.

Q: MC cause of atypical pneumonia?

Mycoplasma pneumoniae. ***Mycoplasma pneumoniae*** - *M. pneumoniae* is the most common cause of **atypical pneumonia**, often referred to as **"walking pneumonia"** due to milder symptoms compared to typical bacterial pneumonia. - It lacks a **cell wall**, making it resistant to many common antibiotics like penicillin and cephalosporins. *Klebsiella pneumoniae* - *Klebsiella pneumoniae* typically causes **lobar pneumonia**, particularly in individuals with compromised immune systems or alcoholism. - It is associated with **severe symptoms**, such as thick, "currant jelly" sputum, and often forms dense consolidated infiltrates on chest X-rays. [1] *Hemophilus influenzae* - *Haemophilus influenzae* is a common cause of **bacterial pneumonia**, especially in children and adults with underlying lung disease (e.g., COPD). - It usually presents as **typical pneumonia** with more acute and severe symptoms, rather than the milder, atypical presentation. *Chlamydia* - While *Chlamydia pneumoniae* can cause a form of atypical pneumonia, it is **less common** than *Mycoplasma pneumoniae* as the primary cause. [1] - *Chlamydia* infections can also cause other conditions, such as **urethritis** and **cervicitis**, depending on the species involved.

Q: Which of the following is anaerobic non-acid fast bacilli:

Actinomyces. ***Actinomyces*** - *Actinomyces* species are **obligate anaerobes** to **facultative anaerobes** that appear as **Gram-positive, non-acid-fast, filamentous rods** (bacilli). - They are classically described as **anaerobic bacteria** and are the prototypical example of anaerobic non-acid-fast bacilli. - They cause chronic infections (actinomycosis) often involving abscess formation with sulfur granules and sinus tracts. *Mycobacterium tuberculosis* - *Mycobacterium tuberculosis* is an **obligate aerobe**, not anaerobic. - It is characterized by its **acid-fastness** due to high mycolic acid content in its cell wall. - Requires oxygen for growth and is the causative agent of tuberculosis. *Listeria* - *Listeria monocytogenes* is a **facultative anaerobe**, meaning it preferentially grows in **aerobic conditions** but can survive anaerobically. - While it is a non-acid-fast Gram-positive bacillus, it is **not classified as an anaerobic organism** in standard microbiology terminology. - *Actinomyces* is the classic answer for anaerobic non-acid-fast bacilli. *Nocardia* - *Nocardia* species are **strict aerobes**, not anaerobic. - They are **weakly acid-fast** filamentous bacteria, distinguishing them from the non-acid-fast *Actinomyces*. - Require oxygen for growth and are found in soil.

Q: Eaton agent is:

Mycoplasma. ***Correct: Mycoplasma*** - The term **"Eaton agent"** refers to *Mycoplasma pneumoniae*, a common cause of atypical pneumonia. - This organism was initially identified by Monroe D. Eaton in the 1940s while studying respiratory infections. - *M. pneumoniae* is a cell wall-deficient bacterium that causes "walking pneumonia" and is resistant to beta-lactam antibiotics. *Incorrect: Pseudomonas* - **Pseudomonas** species, particularly *Pseudomonas aeruginosa*, are opportunistic pathogens often associated with nosocomial infections and infections in immunocompromised individuals. - They are not related to the "Eaton agent" or atypical pneumonia caused by *Mycoplasma pneumoniae*. *Incorrect: Gonococcus* - **Gonococcus** refers to *Neisseria gonorrhoeae*, a bacterium responsible for the sexually transmitted infection gonorrhea. - It causes distinct symptoms in the genitourinary tract and is unrelated to respiratory infections or the "Eaton agent." *Incorrect: Corynebacterium* - **Corynebacterium** species include *Corynebacterium diphtheriae*, the causative agent of diphtheria, which primarily affects the upper respiratory tract and skin. - While it can cause respiratory issues, it is not the "Eaton agent" and has a different clinical presentation and pathogenicity from *Mycoplasma pneumoniae*.

Q: A 47-year-old man with chronic asthma who has been treated with steroids for many years develops a productive cough, weight loss, and night sweats. Imaging studies reveal the presence of abscesses in the lungs and brain. Cultures show gram-positive filaments that are weakly acid-fast. Which of the following organisms is responsible for this patient's condition?

Nocardia asteroides. ***Nocardia asteroides*** - The presence of **productive cough, weight loss, night sweats**, and **abscesses in the lungs and brain** in an immunocompromised patient (due to chronic steroid use for asthma) is highly suggestive of Nocardiosis. - Identification of **gram-positive, branching filaments** that are **weakly acid-fast** in cultures confirms *Nocardia* as the causative organism. *Actinomyces israelii* - While *Actinomyces* causes chronic abscesses and is a **gram-positive filamentous bacterium**, it is **not acid-fast** and typically causes cervicofacial, thoracic, or abdominal infections often associated with trauma or surgery, not disseminated brain abscesses in this context. - *Actinomyces* infections are characterized by **"sulfur granules"** in pus, which are not mentioned here. *Bacillus anthracis* - *Bacillus anthracis* is a **gram-positive rod** that causes **anthrax**, typically presenting as cutaneous, inhalational, or gastrointestinal forms. - It does **not form filamentous structures** and is not acid-fast, and its clinical presentation of rapid-onset severe pneumonia or skin lesions does not match the described chronic progressive illness with multiple abscesses. *Mycobacterium tuberculosis* - *Mycobacterium tuberculosis* causes **tuberculosis**, characterized by cough, weight loss, and night sweats, and can cause lung and brain abscesses (tuberculomas). - However, *Mycobacterium* species are **strongly acid-fast** due to their mycolic acid cell wall and are not described as gram-positive filamentous organisms.

Question 1

Whipple's disease is caused by:

Accepted Answer

Bacteria

Answer

Virus

Answer

Helminths

Answer

Protozoa

Question 2

What is the causative agent for malignant otitis externa?

Accepted Answer

Pseudomonas

Answer

Streptococcus

Answer

Staphylococcus aureus

Answer

Influenza

Question 3

Bacterial vaginosis is caused by all except

Accepted Answer

Proteus

Answer

Coccobacillus

Answer

Mobiluncus

Answer

Gardnerella

Question 4

Most common cause of bacterial meningitis in post-neonatal period:

Accepted Answer

Streptococcus pneumoniae

Answer

Mycobacterium tuberculosis

Answer

Staphylococcus aureus

Answer

Klebsiella

Question 5

Bacillus anthracis is:

Accepted Answer

Gram positive rods with square ends

Answer

Gram negative cocci in cluster

Answer

Gram positive cocci in cluster

Answer

Gram positive bacilli with spherical ends

Question 6

The causative agent for duodenal ulcer is:

Accepted Answer

H. Pylori

Answer

Lactobacilli

Answer

E. coli

Answer

Shigella

Question 7

MC cause of atypical pneumonia?

Accepted Answer

Mycoplasma pneumoniae

Answer

Klebsiella pneumoniae

Answer

Hemophilus influenzae

Answer

Chlamydia

Question 8

Which of the following is anaerobic non-acid fast bacilli:

Accepted Answer

Actinomyces

Answer

Mycobacterium tuberculosis

Answer

Listeria

Answer

Nocardia

Question 9

Eaton agent is:

Accepted Answer

Mycoplasma

Answer

Pseudomonas

Answer

Gonococcus

Answer

Corynebacterium

Question 10

A 47-year-old man with chronic asthma who has been treated with steroids for many years develops a productive cough, weight loss, and night sweats. Imaging studies reveal the presence of abscesses in the lungs and brain. Cultures show gram-positive filaments that are weakly acid-fast. Which of the following organisms is responsible for this patient's condition?

Accepted Answer

Nocardia asteroides

Answer

Actinomyces israelii

Answer

Bacillus anthracis

Answer

Mycobacterium tuberculosis

Bacteriology — MCQs

Bacteriology — MCQs

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